aluminum sailboat hull thickness

• Cruising / Liveaboard
• Sustainability
• Impressions

27. April 2022, updated 6. August 2022

Circumnavigation , Hull Material , Sailboat , Sailing Cruiser , Technical Advice

Sailing Cruisers: The Ultimate Comparison of Hull Materials

Perhaps you have already read our article about the best reasons to live on a boat and we managed to convince you? And now you are looking for a proper cruiser sailboat to turn your dream of living as a liveaboard into reality? Sooner or later, you will definitely ask yourself which hull material is most suitable for a cruiser and this is exactly the question we want to discuss in the following.

Table of Contents

What Materials Are Considered?

The materials used for hull construction of sailboats are GRP (glass fiber reinforced plastic), carbon, Kevlar, wood, aluminum, steel, ferrocement and also various hybrids of these. Some of these materials are not suitable for use in cruisers due to their specific characteristics. Carbon and Kevlar usually only play a role in extremely lightweight high-performance boats typically found in racing, not to mention that they are astronomically expensive.

Wood disqualifies itself due to the extremely costly maintenance and thus it is not practical for use in cruisers. Ferrocement never really caught on as a hull material and primarily played a role as an easy-to-handle material in DIY sailboat construction. This leaves GRP, aluminum, and steel as materials that come into question for us.

GRP vs. Aluminum vs. Steel

In the following, we will take a closer look at these three materials and compare them with each other under various aspects that are important for a cruiser.

GRP is the weakest of the three materials, especially when it comes to impact and abrasion resistance. However, the strength of GRP is highly dependent on its processing quality, as GRP can be laminated in very different ways, which can make for large differences in stability. For example, the first GRP boats built in the 1960s and 1970s often featured much thicker material thicknesses because people were not yet familiar with the material and this resulted in nearly indestructible hulls. There are also some manufacturers who additionally reinforce their GRP hulls with Kevlar or metal inserts. So, there are a lot of differences in terms of stability, but in general a GRP hull is clearly inferior to metal hulls in terms of stability.

In the video below you can see a few crash tests of a Dehler 31, which is made of GRP and takes the collisions impressively well.

Aluminum and steel hulls, on the other hand, have extremely high impact and abrasion resistance, with steel being even slightly superior to aluminum here, as steel is more elastic and has a higher tensile strength. Thus, a metal boat is much more robust and therefore safer than a GRP boat, especially in collisions.

GRP is far superior to steel in terms of weight. For boats up to about 40 feet, it is also superior to aluminum, since aluminum has a minimum thickness of about 5mm making smaller boats heavier than their GRP competitors. Above the 40-foot mark, the tide can turn, and aluminum may be lighter than GRP, but it depends on the exact construction.

Aluminum as a material itself weighs only about a third as much as steel, but the typical weight saving of a hull is typically 20-25% (but up to 50% savings are possible in some cases). This can be attributed to the fact that aluminum requires thicker material thicknesses than steel.

As should already be clear, steel boats are by far the heaviest of the materials we are considering here.

Sailing Characteristics

The sailing characteristics are of course not primarily dependent on the hull material, but rather on other characteristics such as the hull shape, the rig, etc. Nevertheless, certain characteristics are attributable to the hull material.

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GRP boats sail very fast because of their low weight, but the residual flexibility that is unavoidable in the material can cause annoying creaking noises inside the boat.

Aluminum boats, on the other hand, also sail very fast, but much more stiffly and you are not plagued by creaking noises.

Steel also makes for stiff sailing and there are no creaking noises, but due to the enormous weight, a steel boat sails rather sluggishly. However, the high weight also gives steel boats good-natured sailing behavior, which is more likely to forgive too much sail area.

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Interior Space

Unlike metal hulls, a GRP hull does not need an internal reinforcement structure that reduces the space inside the boat. Thus, GRP boats offer a lot of interior space relative to their dimensions.

The stability of aluminum hulls, on the other hand, depends on an internal reinforcement structure (consisting of frames and stringers), which takes up some of the valuable space inside the boat. Especially for smaller boats this can be more important than you might think. In the image below you can see the construction of an aluminum hull built by Dutch shipyard KM Yachtbuilders.

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Steel boats also need such a reinforcement structure, but it is much more compact than that of aluminum boats, thus offering more interior space.

Insulation Properties

Due to its sandwich construction, GRP is inherently a poor conductor of thermal energy and therefore requires little insulation and, under certain conditions, none at all. Along with the good insulating properties, GRP boats also have less condensation to contend with than their metal competitors. In addition, it also has good sound insulation.

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Aluminum and steel boats have very similar properties in terms of insulation. Both materials are very good thermal conductors, which makes good insulation essential. Due to the cold bridges found in metal boats, a lot of condensation occurs inside the boat. The sound insulation of metal hulls is also poor.

Visual Design Options

GRP hulls offer a lot of room for styling, since gelcoats are available in all possible colors and applying them is easy. Another big advantage of GRP is that round shapes can be realized very easily with this material, which makes ergonomics and design very appealing.

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In contrast to GRP boats, round shapes in metal boats can only be achieved with significantly more cost as this requires a lot of effort and special skill in welding. The many welds on metal boats can in some cases look rather rustic, which may bother some people.

Aluminum hulls usually leave the shipyard unpainted, as painting them is very time-consuming and expensive and therefore rather unusual. The raw aluminum look does not appeal to everyone.

Steel boats can be painted as desired, but they almost always have minor visual rust spots somewhere, which are hardly avoidable.

Safety During Thunderstorms

Unlike metal boats, a GRP boat offers no protection to the boat, equipment, and crew against lightning strikes, and you are dependent on a proper lightning conductor system.

In contrast, boats made of aluminum and steel provide excellent protection against lightning strikes purely due to their construction, because they act as a Faraday cage – the inside of the electric field created by a lightning strike is reliably shielded.

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Risk of Material Decomposition

A known risk of material degradation of GRP is osmosis, which occurs when the hull is not properly protected, and moisture can penetrate through the gelcoat where the moisture collects in the hull cavities. The resin in the laminate is decomposed by the penetrated moisture and an acid is produced. Due to its chemical properties, it draws further moisture into the cavities. The pressure in these then increases and pushes the gelcoat outward forming blisters. The brittle gelcoat cracks open and the laminate is progressively decomposed as osmosis continues.

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However, we want to emphasize that osmosis is often overdramatized, and we are not yet aware of any case where a boat has actually sunk because of osmosis. Nevertheless, you should not underestimate this danger and prevent it from happening in the first place through proper care. Unfortunately, structural defects in the hull of used boats caused by osmosis are difficult to see as a non-expert.

In the case of aluminum, there is a risk of galvanic corrosion, in which the base metal aluminum decomposes under the influence of electric current when it comes into contact with a more noble metal. Although such galvanic corrosion can cause considerable damage to the boat within a very short time, this risk can be virtually eliminated if the boat is professionally constructed and regularly maintained. However, this means that any electrical leakage currents must be eliminated, and the many sacrificial anodes must be maintained. Besides, when it comes to electrical installations, you need to know what you’re doing.

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Steel is generally known to be very susceptible to corrosion. Once steel comes into contact with oxygen in the presence of water, rust forms as a result of oxidation. As owner of a steel boat, there is not much you can do against the constant danger of corrosion, except to always make sure that the steel is protected from external elements, which requires a lot of maintenance. In addition, it should be emphasized that the greatest danger of corrosion is the rusting through of the hull from the inside to the outside and not the other way around. Often it is difficult to see all the areas inside the hull and this harbors some undetected dangers.

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Repairability

Even fairly extensive damages in the GRP can be repaired quickly and easily because all you need are fiberglass mats, resin, and hardener. Minor blemishes in the gelcoat such as scratches or small chipping can be repaired with ease.

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Repairing aluminum, on the other hand, is much more difficult, because you first need aluminum plates with the right alloy, and then you also need the right welding equipment. In addition, not everyone has the necessary know-how to weld aluminum properly. Minor blemishes such as scratches can be polished, and dents can be attempted to bulge from the inside. However, if you can’t get to the dent from the inside, you’ll have to live with it willy-nilly.

Steel must be welded as well, but suitable steel plates can be found in most workshops around the world and welding is also much easier than welding aluminum. In addition, the required welding equipment is cheaper and more widely available. The repair of scratches can be easily done yourself, but this is often much more time-consuming than repairing the gelcoat on GRP boats. Dents can be attempted to be removed in the same way as with aluminum boats.

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Maintenance Effort

The maintenance effort is kept within limits with GRP. You should just sand, fill and seal the underwater hull regularly. The great thing about GRP is that such maintenance can be postponed once in a while without having to fear immediately serious consequences (but don’t let it become a habit!).

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Aluminum boats also require little maintenance, as you only need to regularly renew the antifouling coating and maintain the numerous sacrificial anodes, as well as ensure that there is no potential for galvanic corrosion. However, unlike GRP, the maintenance of aluminum boats allows significantly less time leeway, because if galvanic corrosion does occur, it can cause significant damage in a very short period of time.

Steel boats, unlike GRP and aluminum, require constant maintenance, as there are virtually always some rust spots that should be treated early to prevent worse. At regular intervals, the entire hull should also be sand stripped followed by priming with an epoxy system and then sealing with a paint (polyurethane based). Although a steel hull does not rust as quickly as aluminum does with galvanic corrosion, you should avoid postponing maintenance for anything, otherwise nasty surprises can await you.

The cost of GRP boats, from serial and semi-custom production is the lowest compared to those for metal boats. This is mainly due to the fact that a mold only needs to be designed once, which can then be used for all builds of the model. Custom builds, on the other hand, cost significantly more because a mold must be made individually, which involves high costs.

Metal boats are more expensive in serial production as they require a lot of manual welding, with aluminum being even more expensive than steel due to the more complex processing and higher material prices. However, metal boats can be more attractive than GRP for custom builds, but it depends on the individual project.

In addition, it can be said that aluminum boats have a very good value retention compared to GRP and steel boats, which is also reflected in the second-hand market. On the second-hand market, aluminum boats are usually traded at very high prices, whereas GRP boats depreciate significantly and there is a large supply at low prices. The supply of steel boats is rather limited, but the prices for them are nevertheless rather low.

Besides these initial costs, you should also always consider the follow-up costs, because these can make a lot of difference in the long run, especially when you look at the differences in maintenance requirements. Consider how much time and money you will have to put into the boat and even if you want to do most of it yourself, keep your individual opportunity costs in mind.

A Summarizing Overview

In the table below, we have briefly summarized the various characteristics of the respective materials.

An Important Note

Finally, we want to note that there is no such thing as the perfect hull material, because as we have pointed out, each has its strengths and weaknesses. Keep in mind that the properties of the various materials we have discussed are the general ones that apply to most boats. However, the properties of a hull also depend on the specific boat because construction and quality of workmanship are at least as important as the material itself. When comparing different hull materials, you should always keep these differences in terms of construction and workmanship in mind and not compare apples with oranges. It would not make sense to compare a production GRP boat produced under cost pressure with a custom aluminum boat and then conclude that the GRP boat is inferior to the aluminum boat.

Our Recommendation

In general, we claim that for the majority of people a GRP boat makes the most sense. It is very user-friendly in both use and maintenance and is also relatively affordable. We see no reasons against the use in bluewater or for a circumnavigation, although this scene is strongly influenced by advocates of metal boats. We can certainly understand the aspect of increased safety of metal boats, especially in collisions, but we doubt that this justifies the disadvantages of steel or the additional costs of aluminum. Severe collisions are of course a high risk, but always keep in mind how low the probability of such a collision actually is. Nevertheless, we can understand that the increased sense of safety is a very high priority for some.

When using the boat under extreme conditions, such as in Antarctica or Patagonia, we would also want to use a metal boat due to its increased robustness. So, it’s best to ask yourself honestly which areas you actually want to sail.

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In addition, you should also let your own skills and experiences that you have made with the respective material flow into the decision-making process. For example, if you have had a lot of professional experience with steel processing, then you will see the work involved in a steel boat from a completely different perspective… In this sense, listen a little to your gut feeling.

And last but not least, as already mentioned above, it always depends on the specific boat and especially if you are on the second-hand market, you can certainly be a little more flexible with regard to the choice of material and look at the overall package. But we hope that we could help you understand what to expect from the different materials and assist you in making your decision.

If you have any other questions, need advice on your upcoming boat purchase, or want to give us feedback, feel free to post it in the comments, we’ll try to answer everyone!

Happy sailing!

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Aluminium vs fibreglass, which is the best hull material for your yacht?

What’s the best hull material for an ocean cruising sailboat, fibreglass (GRP) or aluminium? It’s an important decision for any boat buyer to make and both materials have their pros and cons. In essence, the right choice depends on two fundamental factors: the yacht’s size and where you plan to cruise. But there are other practical considerations too, some of which might surprise you.

If you’re in the market for a new sailboat and confused by all the contradictory advice and opinions online, here’s what you need to know.

Compare like with like

First, it’s important to compare hulls of the same quality. There’s a massive difference in strength, durability and toughness between a mass-produced GRP hull and a premium GRP hull like our Sirius yachts. An aluminium yacht might be a lot stronger than a typical GRP production yacht but unless it’s heavily overbuilt it won’t be significantly stronger than a Sirius. If GRP laminate is built to last, not just to the minimum specification, you get an almost indestructible boat.

Weight vs strength

Now let’s compare the inherent properties of the two materials. On aluminium hulls, thicker panels are used low down and thinner ones higher up, giving a hull skin that is strong and reasonably light. If aluminium is used to create the skin of the hull, it can’t be much less than 5mm thick without losing too much strength, on a 50ft/15m boat this is fine. However, on smaller hulls, the topsides (the part of the hull above the waterline) can’t go below the panel thickness of around 5mm either, so a smaller aluminium hull has a higher centre of gravity than a larger aluminium hull or a GRP hull (all other things being equal). The skin thickness of the topsides will either be thick, strong and heavy or light, thin and weak. Neither is an ideal solution.

Pound for pound, GRP is lighter and stronger than aluminium, so about half the weight of GRP can be used to achieve the same strength and stiffness

By contrast, GRP does not have an abrupt cut-off point in terms of skin thickness and can be precisely optimised for any part within the hull. Aluminium is isotropic, meaning it behaves the same way in all directions. GRP, like wood, is anisotropic so it behaves differently depending on the direction of force applied. While this might be considered a ‘win’ for aluminium, being able to reinforce or tailor the GRP structure to be much stronger along its load paths without having increase internal reinforcement is a definite benefit for GRP. Lastly, pound for pound, GRP is lighter and stronger than aluminium, so about half the weight of GRP can be used to achieve the same strength and stiffness.

Interior space

Aluminium yachts have less space inside. This is because aluminium sheet doesn’t have the required stiffness without an internal supporting structure. (Actually, it does if you make it thick enough, but we’re talking about sailing boats, not barges.) To keep the weight down, an aluminium yacht hull needs to have a thin skin with reinforcing frames and stringers inside it every half metre, or couple of feet, along the entire length of the hull and all the way around it. This reduces the amount of usable space inside the hull and the space reduction is more significant in smaller yachts than in larger ones.

For a typical aluminium 50-footer (15m) with a beam of around 15ft (4.5m), the supporting frames will be 4-6in thick (10-15cm). To make a comparison, let’s assume that it’s 5in (12.5cm) including the thickness of the hull skin. The frames are on both sides, so the usable interior beam is reduced by 10in (25cm). Thus the yacht loses around 5% of its beam to the internal supporting structure.

If we scale the hull size down to 35ft (10.7m), the frame thickness still has to be the same and now it accounts for 8% of the yacht’s beam.

The way we build our boats and the service we deliver is as unique as our yachts

By contrast, a GRP hull – even one with a Divinycell foam core, like our Sirius 35 DS – is no more than 2in (5cm) thick and it doesn’t need any framework inside for support. This is just 2% of the yacht’s beam, so its interior is 6% wider than one built in aluminium. That translates to 6in (15cm) of extra space, which in practical terms is the difference between being able to comfortably get past someone in the galley and having to squeeze past them.

More space inside also gives you more scope for interior customisation and there’s another practical consideration. The lattice of frames and stringers inside an aluminium hull makes it more awkward to clean and maintain, especially down in the bilges.

This extra space enables us to build the interior on two levels so not only are you getting more width, you are getting extra floorspace thanks to our clever use of space.

Aluminium is an excellent thermal conductor, so aluminium boats need a lot of extra insulation to stay warm in winter and cool in summer. This can be expanded foam, or foam sheets the thickness of the frames. The insulation material adds a bit of weight; more importantly it can also trap moisture and make it difficult to inspect the hull surface from inside.

If expanding foam is used, it tends to make welding repairs more difficult. The foam will need to be cut out from a wide area all around the damage to avoid the risk of the welding equipment starting a fire.

All this added insulation does have the benefit of making aluminium yachts quiet, but we can achieve the same acoustic levels in our boats because of the construction methods, materials and build quality we employ.

Osmosis vs corrosion

Aluminium hulls are immune from osmosis, but so are our premium-quality GRP hulls. We solve the problem by using modern resins and coating the underwater surfaces with epoxy. And be aware that aluminium immersed in seawater has a constant battle with galvanic corrosion, which doesn’t affect GRP.

With expert installation and mounting of equipment to minimise the stray electrical currents that cause galvanic corrosion, an aluminium hull can last for a very long time. Unlike on a fibreglass yacht, though, you cannot install electronic devices or mount deckware without knowing exactly what you are doing. You also have to be careful how you store metal items in the bilges as galvanic and electric corrosion can work frighteningly fast. Throughout its life, too, the underwater surfaces must be well cared for, with plenty of sacrificial anodes and regular, careful inspections.

This is fine if you’re the first and only owner of the yacht, but the ever-present potential for galvanic and electrical corrosion can cause doubt in the minds of buyers. You might know you have been meticulous, but they don’t, and this can affect the value of aluminium yachts on the second-hand market.

Scratching or abrading the underwater antifoul and gelcoat can give shudders to a GRP boat owner. But scratching the underwater surface coating is a real worry for owners of aluminium hulls.

Good GRP hulls can also last a lifetime – and without any special treatment. Many fibreglass yachts built 60 years ago are still happily cruising the world’s oceans today and the materials we use in our Sirius hulls are much stronger and longer-lasting than the basic GRP that those boats were built with.

It’s not just below the waterline where aluminium is more vulnerable than GRP. On deck too, aluminium can be susceptible to crevice corrosion and pitting.

Cost considerations

For small and medium-size yachts, there’s a substantial cost saving with GRP because the material is inherently more suitable than aluminium for efficient series production. It might make sense, cost-wise, to build a 55ft-plus (17m) full custom one-off yacht in aluminium. Any smaller than that, though, and it’s more economical to build the hull and deck in GRP – even with the cost of tooling and mould construction included. That’s why many full custom builders still choose to build in fibreglass, using short-run moulds. For a semi-custom build, like all of our yachts and most other top-quality ocean cruisers, it makes sense to choose GRP and invest the cost saved in upgrading the yacht’s gear and equipment, or in a higher-quality interior.

Ease of repair

For long-distance cruising, ease of repair is an important consideration. The worst-case scenario could involve you needing to repair the boat yourself, in a remote part of the world, which is much easier for you to do if the hull is GRP. You can carry fibreglass mat, resin and catalyst on board, and a repair can often be carried out in less than an hour. It’s also worth bearing in mind that almost any boatyard anywhere in the world can repair a GRP hull and get you sailing again. To repair an aluminium hull you first need to remove the surrounding interior and insulation to minimise the risk of fire, source the right grade of aluminium (unless you take spare panels with you), then find someone with TIG welding equipment, the power to run the equipment close to the yacht, and the knowledge and skills to use it.

Wear and tear

Another consideration is the appearance of the yacht. The battleship grey of bare aluminium can look purposeful but it can’t be described as attractive. Painting it is difficult, expensive and most aluminium yacht builders don’t recommend it. Gelcoat, on the other hand, comes in all shades of colours and any cracks or scratches can easily be repaired for a relatively low cost.

When aluminium yachts get dented or scratched, they tend to wear their scars with pride. Dents can be hammered out if you can access the inside of the hull at the right place, but if you can’t, there they stay.

It’s not just the boat, that takes knocks, you do too. A GRP cockpit can have all the seating and edges nicely rounded; GRP is more forgiving on the body than metal is. This makes the cockpits of GRP boats more comfortable and easier to live with.

How are you really intending to use your boat?

Aluminium does have a higher puncture resistance and a much higher abrasion resistance than GRP. That’s why it’s favoured by expedition yachts that are designed and built specifically for long-term polar exploration, navigating in pack ice and getting ice-bound in harbours on a regular basis. If those are your plans, or if you want a large, full-custom yacht, you can get the hull built by a specialist aluminium fabricator and then fit it out accordingly.

If you’re looking to buy an aluminium yacht with the thought that one day, maybe, you perhaps might go to the Arctic, are you prepared to live with the downsides of aluminium until that time? Will that time ever come? We see SUVs and 4×4 vehicles on the road all the time, bought with the thought that they can go off road, or for the really bad weather that happens once every few years. Until that time, the owners have the downsides (poor fuel economy, mediocre handling, high luggage area, a step up or down every time you go somewhere) to put up with every single day.

If you still want a “go-everywhere cruiser” but your plans involve less extreme sailing for most of the time with occasional high-latitude cruising, there’s a strong argument for choosing GRP. Our extremely strong hulls can be reinforced even further with layers of Kevlar to safeguard against ice punctures. We already have crash boxes in the bow as standard, and we can also fit stainless steel bow protectors or any other solution you want.

Plenty of GRP boats have sailed through the North-West Passage and some have even transited the North East Passage in recent years. These include standard mass-produced yachts that are nowhere near as strong as a Sirius. And throughout the other 98% of the world’s cruising grounds, for all the reasons above, GRP is clearly the best material for a sub-50ft ocean-going yacht. That’s why the vast majority of yachts, including long-distance cruisers, are made of GRP.

General Manager – Torsten Schmidt SIRIUS-WERFT GmbH Ascheberger Straße 68 24306 Plön/Holstein

Fax: 0049 – 4522 – 744 61-29

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The Pros and Cons of an Aluminum Sailboat

There's a lot of legend surrounding aluminum sailboats. But not all of it is true. So what are the pros and cons of an aluminum hull? Let's find out.

What are the pros and cons of an aluminum sailboat? Aluminum sailboats need a lot of maintenance; especially when they are located in saltwater. They need to be painted quite often (every 2-3 years). They are expensive upfront. However, aluminum is a very strong and lightweight material. If done right, an aluminum sailboat can last forever, and can be very fast.

A lot of people think aluminum is a bad material for sailboats. But it's not all bad: aluminum also has its upsides. Most of the problems with this material are due to bad build quality. So the design is bad, not the material.

On this page:

Pros and cons, why does aluminum get such a bad rep, some considerations on aluminum sailboat maintance, reputable aluminum hull builders, related questions.

Some say aluminum is the worst material, others say it is the best. In general, sailors who have actual experience with aluminum hulls are very positive, even saying it is exponentially better than fiberglass and steel.

The quality of aluminum used is crucial. If it's not up to par, it will corrode VERY quickly. So you need a reputable boat builder that only uses marine-grade aluminum.

Aluminum has a bad rep. That's because there are a lot of cheap, badly-built aluminum boats on the market. Its a shame: aluminum can be the ultimate boat building material. But you need to pay attention to details when building or buying one. If neglected, aluminum can corrode away quickly.

Below I'll list all the pros and cons of this material.

Good strength to weight ratio - Aluminum is very lightweight and very strong. One of the most important factors that determine your speed is the displacement of the hull - aka the weight. A lighter boat is faster. So a well-built aluminum boat is faster, and also stronger than fiberglass.

10 times stronger than fiberglass - Don't pin me on that number, but aluminum is stronger than fiberglass. Fiberglass tends to crack when under stress. In a collision, aluminum will probably just dent. A dent is not that big a deal. A crack is - you will eventually sink.

Lighter than all other materials - Aluminum is lighter than steel, wood, and fiberglass. While steel is as strong as aluminum, it's very, very heavy, so that's not great. Wood is heavy as well, and prone to rot - so aluminum wins. Even the lightweight fiberglass is more heavy than aluminum, while it isn't as strong.

Doesn't rust - Aluminum doesn't rust, so, as long as it's above the waterline, you don't need any paint to protect your deck. So while you need to be careful in the bilge, and everything that comes into contact with (salt)water, the rest will be absolutely fine without much attention.

Small boats are cheaper - Custom aluminum boats are cheap to build because aluminum doesn't require a mold like with fiberglass. The builder simply cuts the sheets to size and welds the hull together. It's an easy and fast material to work with. The material itself is also cheap. But it also means that larger boats are more expensive, because the price of an aluminum sailboat mostly consists of labor costs.

Scratches aren't a big issue - Because aluminum doesn't rust, scratches aren't a big issue. If you scratch your top paint while docking, it will practically heal itself, thanks to oxidation.

Lower insurance rate - Insurance companies offer lower rates for aluminum sailboats because they tend to get a lot fewer claims from them.

Lifetime hull warranty - Because a well-build aluminum sailboat hull lasts a lifetime, some manufacturers give you a lifetime warranty on it.

Won't crack - If you hit a rock, your hull won't split open like a fiberglass one. You'll just be able to carry on, which can be a game changer. This also goes for the deck, which means you'll never have leaks -period - if you maintain your boat properly. This is probably the greatest advantage of aluminum over other materials.

Small repairs are easy - Small dents and cracks are easily repaired: they can simply be welded. However, welding aluminum is a bit more complicated than steel, and it requires a lot of skill to create strong welds. It's not as easy as fiberglass, which you can simply patch up using epoxy.

Material is easy to modify - You can literally cut aluminum with a regular sheet cutter. It's a very easy material to modify, and as long as you make sure any attachment points are properly treated for corrosion, you can very easily change things around with just regular tools. It becomes more difficult if you need to weld stuff, then get help from a professional. Especially if it's structural stuff.

More complex anti-fouling paint - You will probably have to paint the hull below the waterline more often than you're used to. Also, you need bottom paint without copper oxide. Due to the oxidation of aluminum, any kind of deck paint you apply will form bubbles after a couple of years. Some people don't paint the deck at all, which is perfectly fine.

Electrolysis and galvanic corrosion - Aluminum is prone to electrolysis and galvanic corrosion. Electrolysis is the chemical reaction of metals with saltwater. When metal comes into contact with saltwater, an electrical current runs through the metals: it turns your boat into a battery, basically. You need to place anodes on your boat to protect your hull. I'll explain electrolysis in detail below.

You need an anode - Sacrificial anodes protect from galvanic corrosion. If you have an aluminum boat that's in saltwater permanently, you definitely need anodes to protect it. A sacrificial anode is basically a piece of metal that's more anode than aluminum, causing it to corrode before the aluminum starts corroding.

Fittings are more complex - Due to electrolysis, adding fittings is more complex. There's really no error margin here. Wherever your alu hull meets another piece of metal, it needs to be thoroughly painted, fitted, and maintained. Otherwise, corrosion will form pretty quickly. A boat without proper isolation between the aluminum and other metals will weather away pretty quickly.

Hull repair is expensive - Aluminum is more expensive than steel, and finding a skilled aluminum welder can be difficult. So it can really cost you if you need to repair the hull. However, a good welder will be quick, which will save you in labor cost.

Large boats are more expensive - Since aluminum boats are welded together instead of casted, the labor cost increases exponentially with length. Quality, large aluminum yachts are way more expensive than fiberglass yachts. But they are a lot cheaper in the long run since they are made of a stronger material.

Weak welds - Welds on aluminum are prone to contamination. This simply means that they're more likely to contain gas bubbles. Which of course makes them weak. This isn't a problem for the top aluminum welders. Good boat builders use very skilled welders. But cheap aluminum boats are hastily put together, and the welds can be a real problem. So make sure to only buy good quality build when you're looking for aluminum.

Lots of low-quality alu boats - There are a lot of low-quality alu boats out there. Especially US build boats have a bad rep. Because aluminum is so cheap to build, lot's of cheap alu boats are being built. And that means that the overall build quality is lower. So the welds aren't as strong, the hull isn't well-constructed or fitted. If you're buying an aluminum boat, you really need to watch out for these budget ones.

More noise from water on the hull - Water crashing into aluminum makes a lot more sound than water crashing into fiberglass. Nothing disastrous, but important to know in advance.

Condensation - Old aluminum hulls (and steel ones as well) suffer from more condensation than fiberglass. However, this is only the case if the boat is not well insulated. Modern aluminum hulls are properly insulated, so condensation shouldn't be a problem. So if you own an old boat, be prepared for a damp interior every now and then.

Large repairs are difficult - You'll need a professional welder for doing large hull repairs. Not many welders are proficient in aluminum welding, so be aware that this might cost you a pretty dollar.

Wiring needs to be done carefully - Because of the risk of electrolysis and galvanic corrosion, you need to be extra careful with wiring and electrical systems. You don't want any electrical current running to the hull, and you really don't want copper wire clippings in your bilge. It will create small holes or pockets in the hull, which may even sink you when unnoticed for too long.

Aluminum is cheap to build with, so it's used a lot for budget boats. As a result, most aluminum boats are hastily put together, so of bad quality. The thing with aluminum is that if it's used in the wrong way, it will become less and less very rapidly.

A lot of cheap (US) boats are welded badly, or just spot welded, making the hull weaker. So these boats are not very suitable for open seas, as they can't take the current.

Another reason is that aluminum is a popular material for self-builders. Believe it or not, but sometimes self-builders don't deliver the quality needed for a boat that will last you a lifetime.

But it's not really fair because a hull that's welded properly is very strong and will last you a lifetime.

Overall, if you stick to reputable boat builders, and make sure to get advice from a boat surveyor that's specialized in alu, you'll be fine. It may even be the finest boat you've sailed.

Aluminum Hulls From Other Countries

Especially aluminum hulls from France, The Netherlands, Australia, and South Africa are of better build quality. United States manufacturers have produced a lot of aluminum hulls of bad quality. But these are mostly inland, flat bottom boats, pontoon boats, power boats, and so on. There are actually very good US and Canadian sailboat builders as well.

When you have an aluminum hull, your number one concerns are electrolysis and galvanic corrosion.

Aluminum is anode to almost all other metals, except for zinc and magnesium. That means that when it's in contact with other metals, aluminum will corrode away. This is called galvanic corrosion.

So you will have to install a sacrificial anode. You will also have to replace this quite often, (on average every couple of years, but in some conditions every couple of months, or even weeks).

I recommend to use OEM anodes. If you don't want to, this is the kit you want (click to check current price on Amazon ).

Make sure everyone who steps onboard puts all of their cash change in a jar. You don't want any metals in your hull. A copper coin that's left unseen can ultimately sink you.

If you add an electric current to this process, it speeds up the corrosion. This is called electrolytic corrosion. This can happen if you have a short in your electrical wiring. Aluminum, in particular, can corrode away very quickly this way. So you need to make sure your wiring is properly insulated. You don't want any electrical current running through your hull!

In general, you need to be extra careful with electrical systems and wiring on an aluminum boat. You also need to pay attention to the marina. If you dock your boat besides steel boats, this can increase the galvanic corrosion. If you add dock power to the mix, your baby starts devouring anodes like it's chicken noodles.

Aluminum also needs a lot of attention paint wise. All fittings and the bottom needs to be painted more often than fiberglass. It's important to keep up with corrosion; once saltwater comes between your fittings, there's no stopping it.

But the horror material some people claim aluminum to be is just not true. There are experienced sailors out there with tens of thousands of miles on there aluminum hull, that still use the original paint. They only repaint the bottom every couple of years.

So where to start? Here are some reputable aluminum sailboat builders:

• Kanter - One of the best North-American aluminum builders. Canadian. Very good-looking boats
• Alubat - smart designs and well build, from France
• Ovni - well-known range from Alubat
• Garcia Yachts - France
• Futuna Yachts - Also French
• Boreal - French yachts

What is the best material for a boat? The best material for a boat depends on the water and sailing conditions, but generally aluminum is the ultimate boat building material. It has a very good strength-to-weight ratio, which is important for a boat. It does, however, require proper maintenance. Especially in saltwater, it needs quite some maintenance, due to electrolysis.

Is aluminum stronger than fiberglass? Aluminum is up to 10 times stronger than fiberglass. It's one of the strongest hull materials if properly built. Fiberglass will crack on impact, which creates leaks. Aluminum doesn't crack as easily and is famous for never leaking. Aluminum is, however, prone to galvanic corrosion, which fiberglass is not.

What's the difference between galvanic corrosion and electrolysis? Electrolysis is an oxidation process in which metals corrode when submerged into an electrolyte. It leads to galvanic corrosion. The most anode metal will eventually corrode. When an electrical current is added to the electrolyte, it speeds up the corrosion process; we call this electrolytic corrosion.

Photo courtesy of Richard Tanguy - CC BY-ND 2.0

I would suggest also to see what is Strongall from Meta, a well known boat maker in France

Mario Jugend

Great article, do you know Lloyds Ship Brisbane, how would you classify them? Thanks

Thanks for a very useful and well done story comparing the two materials. Makes aluminum look more interesting - like Garcia boats. Well done!

Howard Conant

Shawn, Thanks for the good article.More than 30 years ago we embarked on a project to build our 51’ aluminum cutter Holy Grail. Please see www.sail-our-world.com. I still think aluminum is the finest boat building material available for sailboats.

In your first paragraph, “What are the pros and cons of an aluminum sailboat?” what follows in bold might lead to some confusion, as the sentences do not identify which assertions are Pros and which are Cons. Also, on your statemet that aluminum needs painting every 2 or 3 years, that is only, IF YOU PAINT IT. But why would you? Agreed, aluminum does not like paint. And fortunately, it does not NEED paint. Our Holy Grail is only painted under the waterline and on deck to create a nonskid walking surface. Otherwise, paint is not needed. In 29 years of service, the underbody primer coat of paint has remained perfect. It was applied correctly and has served as a barrier coat which has never needed renewing. Further, it is that crucial coat that protects the alu.

Does anyone have any experience with Herley 3400 Solar Power Catamarans? Is the company known for good build quality?

I’m seriously interested in buying one.

https://powercat.herleyboats.com/powercat-3400

You got my attention when you said that aluminum is stronger than fiberglass since fiberglass tends to crack when under stress. This is something that I will share with my husband since he is planning to buy a quintrex boat. He said that he wanted to use the boat every Sunday for his fishing and boating trips, and it makes sense to choose a boat that will last for a long time.

We are looking at a boat made in Italy from Cantieri Navali. I trust made in Italy but does anyone know if it’s a good make? Thank you!

Elina Brooks

It’s good to know that while aluminum might be lighter, it is ten times stronger than fiberglass, so the boat will only dent during a collision. I’ll be settling in a house near the coast starting this summer, so I wanted to get a boat I can use from time to time. I’ll be sure to consider one made of aluminum once I find a boat dealer to contact about my purchase soon. https://www.xtremeboatspc.com/

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Be Bold. Be Antifragile.

OVNI 430 aluminum sailboat

Priced starting at 545,000 €, building on the success of tried and tested sailboat design.

Alubat’s experience and expertise in building blue water 100% aluminum sailboats  in collaboration with MORTAIN & MAVRIKIOS and CBA design agencies, meant that the upgrade from the OVNI 400 to the OVNI 430 was bound to be a success.

The OVNI 430 aluminum sailboat is part of the new generation of sailing yachts combining innovation, ergonomics, comfort and performance.

A new generation of aluminum sailboats

The aluminum hull with an inverted and voluminous bow gives the boat a longer waterline. The sailboat hull is built using semi-thick aluminum resulting in a lighter overall structure (10mm for the bottom plate, 8 mm for the rest of the hull). 

There is also an increase in volume in the front two thirds of the hull, creating extra space in the forward lockers. This results in a larger sail locker and a deeper anchor locker.

Another change from the previous sailboat model is the addition of another chine in the structure. This chine, combined with other changes to the hull, means that the centerboard lifts all the way inside for better hydrodynamics while sailing as well as a better position when beached.

The benefits of the  lifting centerboard allows navigation to shallow waters when searching for protected anchorages, and increased heavy weather downwind sailing performance and safety .

The NACA profile centerboard is built in cast iron can be manually lifted using existing winches.

Benefits of a redesigned deck: Better sail management and ease of movement

The benefits of the aluminum hull design are further enhanced with a new deck. For example, the coach roof is slightly widened as compared to the 400, and the coach roof angles are also modified that results in a raised deck salon interior layout.

Unlike the Ovni 400 sailboat that had an arch specifically for the mainsheet, the mainsheet on the new Ovni 430 aluminum sailboat is now on the coach roof. With that modification, both the Genoa and Staysail sheet passages have also been improved.

Further improving sail management and performance, the boom is slightly lowered, and the integrated double bowsprit and forestay have been moved further ahead.

Another change to the deck is easy access to the stern lockers from both the cockpit and aft. There is also additional volume in the life raft storage locker. 

raised deck salon: modern interior sailboat layout

The new sailboat hull and deck design allow for a raised deck salon layout with panoramic views both while sailing and while at anchor. The navigation station is also raised for active watch keeping. 

The salon is offset to the port side and creates an open and connected interior space, and thanks to the windows and opening portlights surrounding the salon, the space is always light and airy. The galley is located on the starboard side and, again, visibility and ventilation are a key hallmark of this new modern layout design. 

Next available delivery

November 2026

January 2027, exterior gallery.

As part of the new generation of sailboats, the new aluminum Ovni 430 combines innovation, comfort and performance.   The inverted bow gives a longer waterline length to improve performance and expands both the interior and exterior volume.  A new, inclined and watertight companionway door is both secure and easy to operate.

Interior layout

The Ovni 430 sailboat improves on the tried and tested design of the Ovni 400 sailboat. An upgraded raised interior features panoramic view for active watchkeeping, great light and ventilation. An offset salon on the port side opens the interior area.

A large owner cabin is located forward and highlights the new, modern layout and design.  

tour the ovni 430 aluminum sailboat

Specifications.

• Architects : MORTAIN/MAVRIKIOS & CBA
• Material : Aluminum 5083 H111 and 6060 T6 profiles
• Hull Overall : 12.90 m | 42.3 ft
• Hull Length : 12.28 m | 40.3 ft
• Length at Waterline : 11.54 m | 37.9 ft
• Maximum Beam : 4.36 m | 14.3 ft
• Draft with Centerboard Down : 3.40 m | 11.15 ft
• Draft with Centerboard Up : 0.85 m | 2.8 ft
• Air Draft : 18.50 m (60.7 ft) excluding aerials
• Displacement (light) : 11,900 kg | 26,235 lb
• Ballast Weight : 3,330 kg | 7,341 lb
• Keel Weight : 700 kg | 1,543 lb
• Water Tanks : 450 l (119 gal)
• Fuel Tanks : 580 l (153 gal)
• Black Water Tank : 50 l (13 gal)
• Upwind Sail Area (sloop) : Traditional 85 m² (915 sq ft)/ Square top 93 m² (1001 sq ft)
• Mainsail : Traditional 44 m² (474 sq ft) / Square top 52 m² (560 sq ft)
• Solent : 41 m² (441 sq ft)
• Engine : VOLVO D2-50 shaft drive 36.5 kW (50 hp) Optional upgrade available.

equipment list

A well equipped ovni 430 is priced at 789,304 €.

This sample price represents a fully equipped Ovni 430 aluminum sailboat. Additional premium equipment is included in order to meet the requirements of a long-distance sailor. Note: items in bold are in addition to the standard equipment list.

hull & deck construction

• Integral aluminum chine construction with a watertight bulkhead at the front and a crash box
• Welded structural reinforcements
• Welded and bolted mooring cleats
• Aluminum toe-rails integrated into the hull
• Welded seacocks
• Marine-grade plywood and solid wood trim
• Iroko hardwood (teak substitute) for external trim
• Dinghy engine storage located on the bathing platform
• Aluminum chain-plates with stainless steel bushes
• Non-skid paint on deck
• Deck painting process with primary epoxy

deck Fittings

• Stainless steel double lifelines on ss stanchions with side opening gates
• 1 x forward cabin hatch
• 2 x additional hatches on the coach roof with ventilation and blinds
• 6 x fixed hull portlights
• 2 opening aft portlights on coach roof - 1 port and 1 starboard
• Panoramic Plexiglas coach roof with 7 portlights and curtain for privacy
• 2 blocks for mainsail sheet. Mainsheet on coach roof.
• 1 electrical winch 48AEST on coach roof
• 2 additional winches 48AST for staysail
• 2 electrical winches 48AEST on cockpit instead of manual
• 2 Genoa sheet tracks with 1 piston adjustable traveller car
• 2 double pulleys with clamps, return sheet leads on winches
• 2 locking winch handles
• 2 sheaves boxes (x6) leading to halyards and reefs back to the cockpit
• Cam clutches on the coach roof for halyards, reefs and downhaul
• Aluminum grab rails welded on coach roof and 2 aluminum grab rails welded on transom
• Pulpits at mast base
• Bathing platform with stainless steel swim ladder and lockable liferaft storage
• Water, fuel and black water deck fittings
• Hot and cold water shower on bathing platform
• 4 harness clip-in attachment points (companionway, helm station and bathing platform)
• Aluminum aft arch for accessories, 1 LED stern light, and and mooring cleats for lifting dinghy
• Block and fairleads with cam clutch for Genoa furler line feeders

Anchoring & mooring

• Aluminum bowsprit with two bow rollers
• Integrated stern roller
• self-draining chain locker, cable clinch and cleat
• Vertical electric windlass 1200W chain grab Ø10mm
• Anchorage Package (fore & aft): Spade Anchor 25kg + 60m of Ø10mm chain grade & 7,1kg Fortress Anchor + 40m of mixed rope/lead Ø18mm anchoring line
• Windlass control at the helm station
• 2 bow and 2 stern mooring cleats 330mm, 2 midship spring cleats 330mm, additional 2 mooring cleats on foredeck 330mm, and 2 mooring cleats on the rear skirt 330mm
• Mooring Package: 6x fender with sock + 1x White Step-fender, 4x 10m Ø16mm mooring ropes + 2x 15m Ø16mm mooring ropes

Sails & Running Rigging

The sails are all high-tech Pro-Radial woven polyester sails made by Incidence Sails in La Rochelle, France. Included are the following:

• Full batten mainsail 52 m2, 3 reefs including 2 automatic reefs, lazy bag and battens, Spectra halyard. Running backstays and blocks. Hydra Net radial sailcloth
• Furling Genoa (41 m2), UV stripe, bag. Hydra Net radial sailcloth
• Furling Code 0 with sheets, blocks, and Dynema halyard
• Furling staysail, sheets, blocks, Dynema halyard, sail bag
• 1 mainsail halyard, 1 Genoa halyard, 1 boom topping lift, 2 Genoa sheets, 1 mainsail sheet. Additional halyard for Code 0/Spinnaker
• Anodized aluminum deck stepped mast, double swept aft spreaders, 4 mast steps include 2 to reach mainsail and 2 mast steps at the head of the mast.
• Mooring and masthead navigation lights, halogen deck floodlights and tri color mast head. Tri color and white LED mast head light
• Girouette WINDEX at mast head
• Anodized aluminum boom fitted with outhaul and 3 reef lines back to cockpit
• Rigid boom vang with tackle
• Mast step/pod with blocks
• Stainless Steel standing fractional rigging: 1 forestay and 2 backstays, 2 upper shrouds, 2 inner shrouds, 2 aft shrouds
• Large self-draining cockpit with direct access to bathing platform through aluminum tipping bench
• 2 dorade boxes in aluminum welded on the coach roof for ventilation
• Synthetic teak on bathing platform
• Synthetic teak on bench seats and and helm seat with upholstered seats and backrests in choice of color marine fabric
• Coaming lockers with permanent ventilation of aft cabins
• Locking cockpit lockers on portside
• 900 twin steering wheels, compass and compass cover at each helm station
• Engine control on main starboard station
• 2 LED lights under dinghy davit aft arch (white/red)
• Storage and gas lockers on the rear skirt
• Manual bilge pump
• 2 opening aft portlights on coach roof (one on portside coach roof and one in the technical room)
• Harness clip-in attachment points
• 2 Genoa sheet lockers under main winches

companionway

• Smoked Plexiglas companionway door retractible and watertight. Sets in 3 positions
• Dodger with vertical canvas enclosure with an opening central part
• Welded instrument compatible with aluminum dodger
• 1 leather-wrapped s/s grab rail and 1 grab rail in wood bulkhead
• Solid wood 3 non-slip companionway steps with additional LED lights
• 2 opening aft portlights on each side of the companionway
• Engine access located under companionway steps via hydraulic cylinders

Chart table

• Chart table and seat with storage
• Electric control panel with 12V, 1 x 220V and 1 USB outlets, leak meter, water and fuel guage
• 1 directional chart LED light in red and white
• Raised salon layout with portside L-shaped bench seat and bench seat opposite on centreboard casing with storage under seating. Large fixed table. Upholstered cushions, 12cm thick with backrests
• Lateral shelf behind seating with storage space, 2 additional shelves
• Ash Wood Finish
• 5 x 12V fans
• 2 opening portlight in the panoramic roof for ventilation. Panoramic roof comes with curtains for privacy
• 4 LED overhead lights
• Headroom: 6'5" (1.98 m)
• 12V s/s refrigerator, 2 drawers, 144 L, opening in the running direction
• Gimballed s/s two-burner stove with over with s/s protective rail.
• White staron (synthetic resin) worktop with fiddles
• Storage cupboard under sink with shelves and bins.  Drawers under worktop. Tall cupboards with door and shelf
• 2 LED lights in red/white
• Headroom: 6'4" (1.95 m)

Forward Cabin

• Central double berth with 12cm thick upholstered mattress on slatted bed base . Storage lockers under berth
• Wardrobe, cupboard and shelves for storage
• Opening deck hatch for ventilation and 2 fixed portlights
• 3 overhead light, 2 adjustable LED reading lights with integrated USB outlets
• Headroom: 6'1" (1.88 m)
• Double berth with 12 cm thick upholstered mattress on slatted bed base
• 2 opening portlights on panoramic roof for ventilation.
• 1 overhead light, 2 adjustable LED reading lights with integrated USB outlets
• Headroom: 7' (2.16 m)

aft head / Shower

• White countertop, 2 shelves and mirror mounted on bulkhead
• Separate shower with shower column with mixer (hot/cold pressurized water)
• Opening sail gear wardrobe and water drain
• Manual pump toilet with holding tank
• Sink with hot and cold pressurized tap
• Opening portlight on panoramic roof for ventilation
• 2 LED overhead light, 1 220V outlet
• Headroom: 6’4″ (1.96 m)

Technical room / Aft starboard cabin

• Located starboard of companionway.
• 2 bunk berths
• Access technical room via hatch in the cockpit, and suspended storage in the cabin
• Washer/Dryer DAEWOO mini 3kg
• 2 LED overhead lights
• 1 fixed portlight
• Headroom: 4’9″ (1.50 m)

Sail Locker

• Access by opening deck hatch
• Foresail locker layout and 12 V lights
• Insulation black foam + armacell
• Watertight bulkhead between locker and stem

mechanical / electrical

• D2-50 Volvo diesel engine 50hp in a soundproof, ventilated compartment (option for Yanmar)
• Dual fuel filters
• Max Prop 3-blade feathering propeller
• SPUR rope cutter for engine transmission shaft drive
• Tunnel bow thruster 100kg / 12V
• Solar panels 2 x 130 W total on aluminum support and hard dodger, and MPPT regulator
• Air conditioning reversible 16,000 BTU/220V (2 units)
• Fisher Panda Neo 5000i 4Kw generator
• 230V AC 50Hz Circuit includes Shore-power outlet, bi-polar leak detector and electric panel
• Pack upgrade batteries : 4 AGM 130Ah batteries
• 1 engine battery 90Ah
• Battery charger 60A and 120A load distributor
• Converter 24-220v
• Insulation transformer 3600 W auto 115V/230V
• Additional 115 Ah laternator
• Additional 12-220V and USB sockets
• Water maker AQUABASE - 12 V - 65 l/h with automatic rinse
• Maintenance Kit (anodes, led, fuses, hydro-lube rings etc)
• 30L water heater, 220V supply and via engine heat exchanger
• Custom welded plastic water and fuel tanks
• 2 automatic electric bilge pumps with switch located at control panel

navigational electronics

B&G Electronics Package Includes (sample installation): 

• Triton Navigation Pack and 2 displays
• Autopilot LS 40ST16 and NAC-3 computer with display + control panel + precision 9 electronic compass
• VHF B&G V60 with AIS + GPS and VHF antennas
• AIS B&G Transmitter/Receiver
• Radar B&G HALO 20+ - 36NM range
• ZEUS 3S 9" touch screen at the starboard helm station + navionics map France +Pod
• Remote for autopilot
• Fusion bluetooth radio + 4 speakers

centerboard & rudders

• Lifting cast iron centreboard - NACA profile with manual lifting system
• Twin helm stations in cockpit with twin self-aligning rudders

commissioning

• Commissioning includes: launching, masting & rigging adjustment, one day coaching & 5 days in the marina
• Customized vinyl sticker with boat name + home port initials

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Aluminum Hulls for Cruising Boats

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My wife and I had a chance to see Leonard's 47 foot SV Hawk and Jimmy Cornell's new Exploration 45 by Garcia yachts at the Annapolis Sailboat show last week. What struck me is that two sets of people with a mind boggling number of miles under their keels all over the globe eventually settled on aluminum. Would like to discuss the pros and cons of (modern) aluminum hulls. Some potential areas to consider (not exhaustive): Cost, repairability, repairability in remote areas, maintanence, cost of maintanence, hull life and lifecycle , suitability for different climates, sailing performance, collision protection, crew comfort Josh  

If I had a ton of money and didn't care how long I had to make my boat last, I might go with an aluminum boat. They have the ability to survive some serious boo-boos. But, if I planned on keeping my boat for many years, I'd be a little worried about the ability to make hull repairs once the aluminium starts to get dirty. We had an aluminum boat at work that became unrepairable within 15 years, because the small cracks could no longer be welded. I don't know if that's typical or not, but it opened my eyes that maybe aluminum isn't the maintenance free wonder material after all.  

No hull material is perfect, but in my view aluminium is the best apart from initial cost. Repair is easy and importantly the repair is the same as the original. Some small aluminium boats are constructed out of such thin skin thickness that re-welding is not possible. Some high speed aluminium boats are built out of thin skin thicknesses where fatigue is a factor. These factors are not a problem for aluminium cruising yachts.  

noelex77 said: No hull material is perfect, but in my view aluminium is the best apart from initial cost. Repair is easy and importantly the repair is the same as the original. Click to expand...

Take a look here, this (covers a lot of your questions): S/V Hawk The only concern I would have is that if you are in a marina or on mooring a lot of the time, you may have electorolysis problems especially if the harbor is "hot" (a lot of boats or docks leaking electricity). It seems most of the all aluminum hulled boats spend most time in the high latitudes away from other boats and marinas. If I was a full time cruiser and spent most of my time away from "hot" areas I would definitely consider. As I understand the French are big on the all aluminum hulled boats- they normall do not paint top side or deck to cut down on maintenance. Also the boat must be fabricated from marine grade aluminum (5000 series if I remember right). It is much more corrosion resistant than the stuff at say a hardware store.  

Aluminum sail boats in Europe have been sitting around in marinas for many years and European marinas on the most part are pretty shabby and poorly built. Electrical leakage can happen at marinas but aluminum sailboats built properly with hulls at 10 mm, built out of 5000 aluminum and with proper zinks will be just fine. We have taken our Boreal and put her on the hard in Panama as a precaution to marina problems but we were leaving her there for 6 months unattended. All the Ovnis, Garcias and Boreals are built strong and as long as you are aware that something could happen to a long term unattended boat you should be fine.  

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hannah2 said: Aluminum sail boats in Europe have been sitting around in marinas for many years and European marinas on the most part are pretty shabby and poorly built. Electrical leakage can happen at marinas but aluminum sailboats built properly with hulls at 10 mm, built out of 5000 aluminum and with proper zinks will be just fine. We have taken our Boreal and put her on the hard in Panama as a precaution to marina problems but we were leaving her there for 6 months unattended. All the Ovnis, Garcias and Boreals are built strong and as long as you are aware that something could happen to a long term unattended boat you should be fine. Click to expand...

Thanks Casey, She so far has been a pretty amazing design far better than our expectations in all seas. Cheers  

hannah2 said: Thanks Casey, She so far has been a pretty amazing design far better than our expectations in all seas. Cheers Click to expand...

TQA said: You have to be meticulous about avoiding dropping certain metal off cuts inside the hull. The usual culprit is pieces of copper wire dropped during an electrical installation. This is what happens if you don't take care with copper. UNTIE THE LINES #24 - A Bottomless Pit - YouTube Click to expand...

engineer_sailor said: ...................Would like to discuss the pros and cons of (modern) aluminum hulls............... Josh Click to expand...

As a kid I had a 14' Starcraft with an 18 Evinrude. Ran the guts out of it two summers treading for clams in Little Egg Harbor, NJ. I would routinely load her up with 1,500 to 2,200 clams. What's that, a few hundred pounds anyway. Never had a leak. Not to say your experience wasn't accurate, just mine was different. That said, I poked at a white spot on a aluminum boat ( on the hard) and my knife fell through. Talked to a guy with a big Kanter and he said he had some corrosion issues in an integral water tank space that needed welding. I go steel myself, (gotta love the low resale value) but am intrigued with aluminum and would buy a Boreal in a heartbeat soon as I win the really big lottery.  

How is it easy to repair an aluminium hull? Even with a TIG welder the successful welding of thin aluminium is a specialised skill even if you do happen to have the right welder and adequate electricity on your boat. No way I'd ever be convinced that a crack on an aluminium boat would be easier to fix than epoxying a crack in a GRP hull, especially in a place like the Marshall Islands. I accept that a properly welded repair is more durable than a epoxy-putty patch job but easier? No way. Perhaps if you are staying in a marina in a large city . . . . .  

Stumbled upon this good old boat article: http://www.goodoldboat.com/reader_services/articles/steelboat.php Gary: Maybe the 6000 Alu was part of the issue, perhaps combined with thinner material since it was a power boat? Sounds like newer boats benefit from lessons learned with materials. The right Alu and thickness should be ok. Side note: Noticed Cornell's boat is for sale, the GE 45 on YW Didn't realize Alu was heavily used in commercial vessels, but did spot a 400+ Alu Navy catamaran at the Baltimore Sailabration this year. Josh  

engineer_sailor said: Side note: Noticed Cornell's boat is for sale, the GE 45 on YW Click to expand...

engineer_sailor said: My wife and I had a chance to see Leonard's 47 foot SV Hawk and Jimmy Cornell's new Exploration 45 by Garcia yachts at the Annapolis Sailboat show last week. What struck me is that two sets of people with a mind boggling number of miles under their keels all over the globe eventually settled on aluminum. Would like to discuss the pros and cons of (modern) aluminum hulls. Some potential areas to consider (not exhaustive): Cost, repairability, repairability in remote areas, maintanence, cost of maintanence, hull life and lifecycle , suitability for different climates, sailing performance, collision protection, crew comfort Josh Click to expand...

One issue that two of my cruising friends were faced with was finding highly competent alloy welders. Both spent considerable time in finding the "right" guy. One was in the first world and another in the third world. It may not be just pulling into any old boat yard to get your repairs done.  

srqsailor: I think I misinterpreted the listing on YW. It's a "Jimmy Cornell" version of the GE45 which is a specific layout configuration  

It must be an American thing but the penny thing does not hold up it is all BS. We have a penny sitting in a our bilge area for over a year now and nothing much has been going on. Some dust, some dirt but no pitting. Of course when we were thinking about having an aluminum boat built we asked all the paranoid questions one should ask. Our builder said why don't you put one of your copper pennies in the bilge area and see what it does. I was not about to put one in the very bottom of the bilge but decided to see what would happen if I put one on a ledge of the frame. And guess what we have no corrosion and it is a wet area we put it in. I realize a penny does not have as much copper in it as years past but it still has copper in it. I have found screws, copper slivers from finished wiring in the bottom of the boat none had any effect that would make a hole through aluminum 5000 at 10mm thick. As for that video with the gal who bought a boat with huge corrosion problems. It was a case of improper zink or none at all in a hot marina for a very long time. As I have said before Alaskan aluminum fishing boats have been in service for many years and they have a habit of just leaving all types of non aluminum metals in their bilges. Aluminum is tougher than you think.  

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StuartT New Member

Hi Folks, Since starting to look for the 'next' big hole in the water, I have been focused on 55' to 65' trawlers. While the steel group attracts me for the obvious reasons that have been discussed extensively on this forum, I really hate the idea of chasing rust for the rest of my days. And I really don't see my wife and I cruising beyond the inside passage of the PNW to Alaska, so the glass boats keep looking more appropriate, especially when considering the resale difficulties of a steel boat. Recently this 72' Darling named "North" got my attention. http://northyacht.ca/exterior.html I really like a lot of the features, especially the aluminum hull which is respected in our area due to the many commercial aluminum boats in similar size ranges. I was starting to really get interested until I read that the hull thickness was .250 (see the tab 'Story'). That stopped me dead in my tracks since it is my understanding that in general, if a steel hull is say 3/8" (again, this size range), you look for a 50% increase in aluminum thickness to approximate the strength of steel, i.e. dent, tear, bend resistance. A steel trawler I was looking at was a 60 footer with a 3/8" A36 hull, so this Darling with a 1/4" hull could be considered, what, less than 1/2 as strong as the steel trawler. My arithmetic: .375 + .1875 = .5625 x 44.4% = .250 or stated in fractions, 3/8" + 3/16 = 9/16 x 44.4% = 1/4). I don't want a boat that might be just fine in our Pacific NW inland waters, looks like it should be open ocean ready, but fails the litmus test of strength for future prospective long distance cruisers. What serious owner/captain is going to want to go well offshore if the hull of his boat is a compromise. Maybe the secret is in the fuel capacity. At 1500 gallons and twin 450 C series Cummins, maybe this boat was never designed to be anything more than a costal cruiser. Am I over thinking this? Stuart Thornton

Capt Ralph Senior Member

1/4" allow on the bottom?? Pretty F%^&ng good in my opinion. I've run, pounded, abused and run aground Strikers while I was young with much thinner allow plating than that. Pushed a 70' Roamer with thinner thru 20 years of Bahama abuse. The name escapes me at the moment, some world class custom hit a pinnacle on the left coast (your side) years ago. Over built, single engine (engine fell out the hole during salvage). He thought he was tough. Since, " boat name " II has completed world trips. Not to be depressing,, my point,, Are you breaking ice on the north west passage? 1/4" alloy (fancy alloy numbers involved) is tough. I can not answer your math but a proper surveyor can.. Just don't hit any underwater mountains. I question smart range with 5.9 tuned to 450hp. Not sure here but question it. ,rc

RER Senior Member

rcrapps said: ↑ I question smart range with 5.9 tuned to 450hp. Not sure here but question it. Click to expand...

tristanrowe Member

6.3(ish)mm is fine for hull plating, ask to see the scantlings as you may find it's thicker on the bottom strakes or even the bilge return - either way as long as people haven't dropped steel fasteners etc in salty bilge water you should be fine. Looks like a handsome vessel, my type of boat for sure.

RER said: ↑ The 450C is 8.3 litre. I hope they've changed the oil since 4-9-04. Click to expand...

Yes, they are 8.3L Cummins engines, not 5.9's. Sweet, also yes. Cruise 10 knots, WOT 13. That is a good suggestion to look over the scantlings and see if the critical areas are thicker or were reinforced. I have to assume that this was not overlooked during the engineering of this 50 ton vessel. There is a lot of information online regarding comparisons between steel and alloy as hull material and there seems to be general acceptance that marine alloys will be roughly 50% thicker then marine steel for the same strength. For example, from: www.kastenmarine.com/alumVSsteel.htm "Since an aluminum structure is designed to a deflection criteria, all scantlings are made somewhere around 50% or so larger than they would be for a steel structure. For the sake of an easy example, what would be one inch of plate thickness on a steel vessel would be approximately one and a half inches of plate thickness on the aluminum vessel in order to achieve the same rigidity of structure. " This Al trawler seems to be on the light side of the equation compared to steel yachts I have researched, but then again, I could be missing something about hull design.

Scallywag Member

IMO 1/4 inch is more than adequate. Some naval architects prefer lighter hull design and rely on more ribs/framing to create the necessary rigidity. Others prefer to use thicker plate and less structure. You could say my aluminum hull is very overbuilt and it is 1/4 in places, 5/16 in others, and I believe thicker (3/8) around the prop pockets. I'm sure if you look at the blueprints you will find something similar. BTW I have Cummins 6CTA 8.3L at 400HP and love them on my 70 footer for our style of boating. Cruise at 9 knots and WOT is 12.

I just read "The Full Story" about North. My boat was built by Marine Builders Inc. in Utica, IN in 1992. Looks like North was built by Darling Yachts in Jeffersonville, IN. I'd be willing to bet some of the same craftsmen worked on both boats.

I'd bet you are right on that. Must be a lot of inbreeding of craftsmen among the various yards when they are in the same general area. I think the 'North' website is an older write up on the boat from circa 2005. There are some 0bvious discrepancies between that and the current listing that are notable, not the least of which is the oil filter date. And I am sure a number of the pictures in the current listing were plagiarized from the 'North' website. Seeing it in person will be telling and I hope to do so on a trip to Seattle in a couple weeks. Reminds me of a 60 steel trawler I was interested in which was located in San Diego. The pictures were tantalizing, but when I actually saw the boat, I was disappointed.

olderboater Senior Member

StuartT said: ↑ I'd bet you are right on that. Must be a lot of inbreeding of craftsmen among the various yards when they are in the same general area. I think the 'North' website is an older write up on the boat from circa 2005. There are some 0bvious discrepancies between that and the current listing that are notable, not the least of which is the oil filter date. And I am sure a number of the pictures in the current listing were plagiarized from the 'North' website. Seeing it in person will be telling and I hope to do so on a trip to Seattle in a couple weeks. Reminds me of a 60 steel trawler I was interested in which was located in San Diego. The pictures were tantalizing, but when I actually saw the boat, I was disappointed. Click to expand...

karo1776 Senior Member

Is this hull thick enough, well yes, but it depends. If the framing system is transverse with plate with ribs (vertical framing) usually the hull plating is thicker than a longitudinally framed boat that has only stringers (horizontal framing). Why is the 'hogging' forces. And, hull plating can be thinner that either framing relying soling with ribs or stringers if it has both. Thickness as speed goes up on boats must increase due to the pressure load against the hull from water impinging against it to prevent buckling. Or, in the case of hull plating over the props plating vibration from disturbing the enjoyment of the yacht. Hull plating varies with type and purpose of yacht. Sailboats have proportionally thicker plating for the same design speed than power boats (fairness of hull is more important). But the scary think is if you are talking composite hulls their outer skin thickness can be quite thin due to the presence of core to reduce weight. Usually even now-a-days hull thickness is more than necessary as safety margin against puncture, and often because of classification societies that still rely on rules of thumb scantlings. Which is how all boats were designed before the computer age. As a kid they still produced ships with a few crack stop riveted seams... now they don't as design technique and metallurgy have made the old by experienced guess or golly largely obsolete... reducing safety margins in plating thickness because we know more and can calculate better. Hull plating can be frightfully thin as a ship goes up in size proportionally the hull plating gets thinner. Its like the difference between a typical sized yacht and its plating thickness and an cruise ship. Think of it as much like the banking industry where the safety margins get thinner in proportion to the banks size or the outstanding debt held... but in that case the boat won't sink if it hits the rocks as the government will plug up the leaks... by magic of inflation and tax.

I would have no clue on the proper design criteria but can totally understand where the selection of stringer and ribs, their alloys, structural arrangement, etc. play a huge part determining hull thickness. It may very well be that this 72’ trawler is well designed using ¼” plate. It’s just that as I noted above, another 60’ trawler I have looked into was constructed with 3/8” A36 steel plate, which makes the 1/4” plate on this aluminum vessel 33% thinner rather than greater. I recognize that two entirely different design criteria are probably at work here, but the thickness disparities in the hulls (as comparted to Michael Kasten quoted below) is too diverse to ignore without questioning whether the aluminum trawler might have been built with a completely different set of objectives, like strictly inland or costal waters for example. And before someone brings it up, yes, a knowledgeable, experienced and qualified marine surveyor will probably be able to review the scantlings, take the measurements and properly advise me. But I have to start somewhere, and posing the question here is a lot less expensive to try and flush out something obvious than blindly ordering a haul out, which requires a written offer with deposit, and a commitment to the cost of the surveyor. Why not try asking first? Another reference: http://www.aluminum.org/sites/default/files/Aluminum_at_Sea.pdf “According to marine design engineer Michael Kasten of Kasten Marine Design, Port Townsend, Wash., an aluminum hull designed for equivalent strength and stiffness to a steel hull would be about 50% thicker but lighter by as much as 50% and would have a 30% greater dent resistance and 13% greater resistance to rupture.”

StuartT: Perhaps this will help... in the 1980's Jongert made two near identical motor yachts, one steel "Impossible Dream" now, and the other aluminum "Grand Cu" both are on the market and both are owned by members of YF... and both owners know the scantlings of their respective little ships as Jongert provided those routinely to customers... and Herbert Dahm the broker that sold most of Jongerts yachts back in those days was and is always good at serving his clients, real gentleman too. So some research might help you. Jongert is back in operation sort of, the owners are around, though I cannot remember who the owners are (forum names you know) but you could call the brokers, or Herbert or ask around here and likely find out. Comparing the two apples to your apple and orange situation might help. Also, I bet both owners have pictures of the hulls out of the water... so you can compare hull plating fairness. Why can you do that and get and idea of performance of steel to aluminum... IS because Jongert back in those days made some of the fairest hulls in Holland... and little filler was used. Sadly the Arabs own the thing now after a couple landlubbers.... Jongert and Huisman were really good at hull fairness too... the owners yards were born to demand it... they are all gone now. The motor boats never have fairing done to the hull so you should be able to tell something by seeing the two out of the water after many years (near 30 ) of use. If they are still fair and your smaller boat situation seems to me to have plenty of thickness you should get a sense of proportion. Don't read much into this but an aluminum deforms less from use than a steel hull... bounces back... but just take it into mind.

Keep in mind... steel hulls are built with thicker than required plating to allow for "wastage" as the plating rusts away. So, just because a particular hull was built with 3/8 inch steel, it doesn't mean that is what was structurally required. Plate thickness is increased to allow longer service life.

Just to add some visuals to the conversation. Here is a piece of 3/8" from my hull.

Aluminum one, owner has CD with scantlings Its owner name on YF is rmjranch you can contract here. Here is a link to the Aluminum Jongert showing hull out of water, now renamed Grand Cu. And here is the current sales listing for the Aluminum one above.... wow owner claims to have plans on CD see... http://www.hmy.com/used-yachts/_78_...h_2014_Naiad_Zero_Speed_Stabilizers/4850898/2 I could not find it on Yachtworld, but it is on Yatco as Grand Cu http://www.yatco.com/vessel/info/217025/79ft-24m/1987/jongert-for-sale-aventura-united-states Steel one with scantlings Here is the sales listing for the Steel one... http://www.northropandjohnson.com/yachts-for-sale/3375-impossible-dream/ and at Yachtworld the listing actually has the scantlings see pasted below. http://www.**************/boats/198...Fort-Lauderdale/FL/United-States#.VhvyWbQ07dc CONSTRUCTION Steel Jongert, Impossible Dream Built to German Lloyd’s full classification. Hull: 8mm welded steel keel plating, 6mm and 8mm welded steel bottom plating and 5mm topsides plating. Hull framing includes 180mm by 80 mm by 8mm bottom longitudinals, 75mm by 8mm topsides longitudinals, and 75mmby 8mm traverse framing on 400mm centers with 8mm stringers welded to the frames. Integral tanks within the vessel’s hull envelope provide additional hull structure. Five watertight bulkheads Main Deck: 5mm welded steel plate in 120mm by 80mm by 8mm longitudinal framing and 75mm by 8mm transverse framing. Superstructure: 5mm and 6mm aluminum plating welded onto variously sized “T” bar, angle and plate aluminum framing on approximately 400mm centers. Shafts: 80mm S/S within sealed oilbath tubes 2” high density foam on hull sides and floors throughout (2007) New teak decks (2007) Complete exterior LP paint job (2007)

Scallywag, that is disconcerting to think a steel boat hull specs are "padded". Carrying all that extra weight around just to offset rust? That would be enough to put me off steel right there. karo1776, I am not sure what you are trying to tell me. You found some specs on Impossible Dream and posted them. So we have two boats by the same builder (BTW that all aluminum one is called Grand 'Cru', not 'Cu") but we do not have specs on Grand Cru (previously Morning Cloud) so no way to compare them. The owner of Grand Cru apparently has the CD with the scantlings, but it would be inappropriate for me to request a copy. You picked out these two for a reason but I do not understand the point you are trying to make or how it helps with my question.

My point is this: 1. Simply the two boats were made for the same purpose. 2. That purpose is similar enough to yours. 3. The boats were made by the same manufacturer and naval architect. 4. The boats were of similar size. 5. The boats were made only a year apart... close enough. 6. The boats were made of the two different materials you are concerned with Steel and Aluminum. 7. It situation is rare so a ready practical comparison could be made between thickness of plating, frame spacing and stringers between identical boats, identical manufacturer, at the same time by the same naval architech... etc. 8. Doing that comparison would help give you a practical sense of proportion to make judgment. I am quite sure the owner of Grand Cru would share this information with you as a member of the forum... why not message him and ask ... refer him to this thread... his forum name is "rmjranch". FYI, I would chose the Aluminum boat because aluminum bounces back better than steel so likely will retain its fair original state as manufactured. And, the bilges are easier maintained. A comment on Jongert and Huisman. Back in the 1980s if you meet the operators of the two yards and shook their hands... you would know... they knew how to build boats. Few do now and run the companies. Wolter's hands were very strong and massive in particular... too bad the stress of building Jim Clarks dreams over stressed him at the point in life they came together. And, I doubt you get a home cooked meal when visiting the yard now. To bad that Jongert is no longer what it was not even faint shadow... and I fear the same for Royal Huisman oh well... J'ai peur d'aimer un souvenir "I am afraid to love a memory"...

karo1776 said: ↑ My point is this: 1. Simply the two boats were made for the same purpose. 2. That purpose is similar enough to yours. 3. The boats were made by the same manufacturer and naval architect. 4. The boats were of similar size. 5. The boats were made only a year apart... close enough. 6. The boats were made of the two different materials you are concerned with Steel and Aluminum. 7. It situation is rare so a ready practical comparison could be made between thickness of plating, frame spacing and stringers between identical boats, identical manufacturer, at the same time by the same naval architech... etc. 8. Doing that comparison would help give you a practical sense of proportion to make judgment. I am quite sure the owner of Grand Cru would share this information with you as a member of the forum... why not message him and ask ... refer him to this thread... his forum name is "rmjranch". FYI, I would chose the Aluminum boat because aluminum bounces back better than steel so likely will retain its fair original state as manufactured. And, the bilges are easier maintained. A comment on Jongert and Huisman. Back in the 1980s if you meet the operators of the two yards and shook their hands... you would know... they knew how to build boats. Few do now and run the companies. Wolter's hands were very strong and massive in particular... too bad the stress of building Jim Clarks dreams over stressed him at the point in life they came together. And, I doubt you get a home cooked meal when visiting the yard now. To bad that Jongert is no longer what it was not even faint shadow... and I fear the same for Royal Huisman oh well... J'ai peur d'aimer un souvenir "I am afraid to love a memory"... Click to expand...

Well, I guess I need another kind of help. I do not see a way to PM (private message) a member on this forum. Am I missing something or is it not a forum option?

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What Aluminum Alloy Should I Use to Build a Boat, and Why?

All aluminum alloys are not created equal. 5052. T6-6061. What the heck do these numbers and letters mean? And more importantly, which one should I choose for my boat project ? Like most questions related to materials, the answer of course is “Well, it depends on your application.” To understand which is the appropriate aluminum to choose, it’s important to know a little bit about aluminum, its various alloys, and their properties.

Properties of Aluminum Alloy

Aluminum is an amazing material. Most can easily recognize one of its most distinctive qualities: weight. Compared to other metals, aluminum is incredibly light. It weighs about 1/3 as much as steel, yet has the strength to be used in structural applications, can be used in most fabrication processes, and can be cast, forged, formed, welded, machined, etc. Additionally, it’s particularly great for things that move, and combined with its exceptional resistance to corrosion, makes it an obvious choice for boat construction.

Aluminum Alloy Variations

The Aluminum Association of the United States has developed a naming system for the various alloys found commercially available, of which there are over 500 registered designations. Of the commercially available variations, four are most commonly used in the Marine Industry: 5052, 5083, 5086, and 6061. Typically, these alloys have a heat number of H3, which means they have been strain hardened and stabilized.

All 5000 alloys use magnesium as the principal alloying element. This makes the aluminum easier to weld, which is important for construction. It’s generally the “softest” of the four, and because of this it’s also considered the most workable. This aluminum alloy is not as susceptible to cracking during the forming process and is also the least expensive of the common marine alloys. 5052 is generally used for interior parts of the boat such as cabins, decks, and gunwales.

Aluminum alloy 5083 is commonly used by the US Navy. It’s stronger than 5052, yet it’s still formable and easily welded. This aluminum alloy is widely used in chemical and marine environments where corrosion resistance is crucial and can also withstand extremely cold temperatures without becoming brittle. But, all these great properties come at a higher cost than 5052, and although 5083 is stiffer than 5052, it’s also more prone to cracking. 5083’s corrosion resistance and toughness make it a great choice for hull bottoms and side sheets.

Considered the superior alloy for marine environments, 5086 has similar characteristics of 5083, but with added strength. This alloy is so close to its 5083 brother that the two are arguably interchangeable. In fact, 5086’s strength increases when it is cold worked. The main benefit of this aluminum alloy is its increased corrosion resistance properties, especially in salt water. It is the most popular choice for hull bottoms and side sheets.

This is a great general-purpose alloy. 6061 aluminum alloy can be used for structural components, as it has more strength than the other three listed above. It also has excellent finishing characteristics, so it can be used in areas that are highly visible to increase the aesthetics of the project. This added strength comes at a cost though, as this alloy is not as easily formable, is more prone to fracturing, and is only available in limited sizes. 6061 is commonly used for extrusions or exterior hull reinforcement, such as keel linings.

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The Alumacraft Advantage: The 2XB Hull

Alumacraft owners will often tell you their boat just feels so solid and confident on the water, and they are not imagining that sensation. The exclusive Alumacraft 2XB™ hull design is the reason an Alumacraft V-hull boat offers a ride that’s unmatched in the aluminum segment, a ride that feels solid and sounds quiet across surface ripples or a stiff lake chop.

The result is a boat that offers the ride quality similar to a fiberglass hull yet retains all the advantages of riveted aluminum construction. Alumacraft 2XB stands for “twice the boat.” Let’s take a look at the engineering behind the label. Alumacraft introduced the 2XB hull design in 1996 and has been refining it ever since. Its key element is a double layer (twice the boat) of aluminum sheet on the running surface. Today the doubled bottom covers the entire running surface on Alumacraft Trophy, Tournament Pro, Edge, Competitor and Competitor FXS models.

These are typically the largest Alumacraft models designed for anglers likely to also carry the heaviest load of gear, and more frequently apt to venture out on rough water. Alumacraft Escape , Competitor 165 , Voyageur and Classic models have 2XB double plating from the bow to midship. These models are typically the smaller and lighter boats in the Alumacraft V-hull line .

The 2XB running surface is constructed in one piece from chine to chine with no center seam at the keel. The second sheet of aluminum fits inside the outer layer. The thickness of the aluminum sheet is optimized for boat size.

Boats with full bow-to-stern double plating have either two .080" sheets (.160" combined thickness) or two .100" sheets (.200" combined thickness). For smaller boat models the sheets are typically .080" and .065" (.125" combined thickness). Competing aluminum boats typically have a bottom thickness of no more than .125", even on the largest models. An Alumacraft 2XB bottom is up to 60 percent thicker than those competing models. The double-sheet 2XB design does add some weight to Alumacraft boats, but that weight does not affect hole shot or top-speed performance. Alumacraft boats are designed with a gull-wing-shaped Aquadynamic hull to provide added lift that compensates for this weight. There’s more to the Alumacraft 2XB hull than double plating. Before making aluminum boats, Alumacraft was engaged in fabricating aluminum aircraft components during World War II. To this day every Alumacraft model is assembled with aircraft-grade rivets that meet a premium military specification. These rivets have a larger head and shank than the smaller rivets used to build other aluminum boat brands. Fewer larger rivets are required to create a strong clamping force. Fewer rivets in the boat bottom create less drag in the water and present fewer potential failure points. There’s also added strength in the Alumacraft keel.

Its single-piece design is stronger than the typical two-piece keel, and the keel is formed of very durable heat-treated aluminum that’s a full quarter-inch thick at the wear points. The keel has a deeper profile to improve boat tracking, and the one-piece hull design allows Alumacraft to align the keel with precision to avoid creating turbulence to the motor propeller that could compromise performance.

The Alumacraft 2XB hull combines double-plating, premium rivets and a stiff keel to create a durable running surface that simply feels more solid in the water. To see Alumacraft designs come to life, check out the 2XB and Aquadynamic videos. Learn more about the Alumacraft Advantage .

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Designing Boat Structure Working With the ABS Rule Copyright 2011 - 2016 Michael Kasten   I have often been asked how boat scantlings are determined. For the most part such questions fall into one of the following general categories: How is structure determined for boats...? What are "appropriate" scantlings for an ocean-worthy vessel....? Of course there is not a "one size fits all" answer to the second question, since boats differ greatly in size and therefore have different loads that will be imposed upon the structure. I have written the following article in order to describe my own approach to determining a boat's structure - which amounts to being an answer to the first question. The following article is not intended to be a treatise on designing in aluminum, but rather a general overview of the process and a few of the variables to be considered, most of which are applicable to boats built in any material. As a criterion for structure, I prefer to use the applicable American Bureau of Shipping rules wherever possible. This is because the various ABS rules are based on actual calculations, as opposed to "look-up" tables as are found in many other scantling rules. Via the ABS rules we are able to calculate a minimum plate or panel thickness, as well as a minimum Section Modulus for each member. This "calculated" approach allows considerable flexibility in terms of scantling choices, plate and panel thickness, and the spacing of internal frames, bulkheads, and longitudinal stringers. The exception however is that for plank-on-frame wooden vessels, unfortunately the ABS stopped publishing their wooden vessel rule in the 1960's..! As a result, for plank-on-frame wooden yachts Germanischer Lloyd, British Lloyds Register, and Det Norske Veritas presently offer the best guides to wooden vessel structure. For metal or composite boats, among the many different rules published by Classification Societies that address a boat's structure there appear to be many good options. Even so, I prefer using the various ABS rules, which offers many excellent advantages that are described below. Although the following article uses aluminum boat structures as an example, the following methodology is also directly applicable to steel or composite structure (fiberglass).   ALUMINUM ALLOYS The alloys commonly used for boat extrusions (flat bar, pipe, angle, etc.) are predominantly 6061 T-6, or occasionally 6063 T-6 or 6063 T-5 if there is an availability problem with 6061. A new 6082 T-6 alloy has been introduced that offers slightly improved strength, but which can be quite difficult to find in many of the common extrusion shapes (pipe, flat bar and others). For plate (and any shapes that will be NC cut from plate, such as frames) the most available alloys in the US and Canada are 5086-H116 (the most commonly used alloy with the highest corrosion resistance) and 5083 H-116 (higher as-welded strength, but slightly less corrosion resistance; less commonly specified). If the vessel will be built in North America, New Zealand or Australia, I prefer to specify 5083 or the new 5383 alloy from Pechiney / Alcoa which combines the higher corrosion resistance of 5086 with the higher as-welded strength of 5083.  If the vessel will be built in the EU, I prefer to specify the even newer 5059 alloy developed by Corus in Germany which improves on both the corrosion resistance and the as-welded strength of Pechiney's 5383.   STRENGTH OF VARIOUS ALUMINUM ALLOYS With regard to material strength, it should be noted that each of the ABS rules for aluminum vessels specify different minimum un-welded and as-welded strengths. Wherever a published allowable strength is higher in a given ABS rule, it is usually compensated for by different head pressures being calculated for each region (bottom, topsides, deck, house, tanks) or different credits are applied locally.  This issue has to a large extent been addressed in the ABS Yacht Rule - Materials & Welding - Aluminum & FRP (updated in 2016). In general, structures are designed to the yield strength of the material, plus a margin of safety.  For aluminum, ordinarily the “as-welded” yield strength is used, as opposed to the "fully annealed" yield strength. You can see in the table below that the as-welded yield never approaches the fully annealed condition.  Even so, the ABS rules use the fully annealed condition for each alloy. As a result, the ABS rule assures a considerable built-in safety factor. A summary of the various ways of expressing the yield strength of aluminum alloys is as follows: FULLY ANNEALED YIELD AS WELDED YIELD AS MILLED YIELD 5086 – 0: 95 N/mm^2 - 14 kpsi 5083 – 0: 125 N/mm^2 - 16 kpsi 5383 – 0: 145 N/mm^2 - 21 kpsi 5059 – 0: 160 N/mm^2 - 23 kpsi * 6061 – 0: 110 N/mm^2 - 16 kpsi 6082 – 0: 110 N/mm^2 - 16 kpsi* 5086 – H-116: 131 N/mm^2 - 19 kpsi 5083 – H-116: 165 N/mm^2 - 24 kpsi 5383 – H-116: 185 N/mm^2 - 27 kpsi 5059 – H-116: 195 N/mm^2 - 28 kpsi ** 6061 – T-6: 138 N/mm^2 - 20 kpsi 6082 – T-6: 144 N/mm^2 - 21 kpsi ** 5086 – H-116: 195 N/mm^2 - 28 kpsi 5083 – H-116: 215 N/mm^2 - 31 kpsi 5383 – H-116: 230 N/mm^2 - 33 kpsi 5059 – H-116: 270 N/mm^2 - 39 kpsi * 6061 – T-6: 240 N/mm^2 - 35 kpsi 6082 – T-6: 260 N/mm^2 - 38 kpsi * All values above are from the 2016 ABS Yacht Rule except for the following: * Values as-published for alloy 5059 in the GL Rule . ** As-welded values for alloy 5059 ( interpolated based on as-welded yield for other alloys). We can see from the above that there is quite a variation in the strength of each one of these alloys depending on their " temper ".  There is also a considerable variation in strength between alloys regardless of their "temper".  For my own designs, in order to make use of the most conservative strength values I use the fully annealed material strength as is most often specified within the ABS rules.  In addition to using the fully annealed condition, for the scantling calculations I generally assume the lowest strength alloy (5086) will be used unless it is KNOWN for certain that a specific higher strength alloy will be available and will be used. This approach allows use of 5086 throughout if that is all that's available to the builder. Then if a higher as-welded-yield strength material is used, the vessel will simply be that much stronger, however in all cases the ABS rule will still have been satisfied. This can result in heavier weight than is necessary if 5383 or 5059 plate happens to be available. Therefore in a weight-sensitive application, there is plenty of room for optimization of the structure to suit the higher fully annealed yield strength of 5383 or 5059 alloys.   APPLICABILITY OF THE ABS RULES...  The ABS scantling rules that have most commonly been used for yachts are as follows:    1994 ABS Offshore Racing Yacht Rule (ORY) - Originally applied to ALL sailing yachts in wood, GRP, steel and aluminum up to 100 feet in length (30m).  In 1996 the scope of this rule was limited to sailing yachts between 79 feet (24m) and 100 feet (30m) without any actual changes to the rule.  Due to this limitation in scope, the ABS ORY rule has effectively been replaced by the 2016 ABS Yachts Rule (see below). This rule was apparently the theoretical basis of the RCD ISO-12215 rules for yacht structure which is used in the EU for all yachts under 79 feet (24m) therefore it is very odd to have its scope limited to yachts above 79 feet.    2000 ABS Motor Pleasure Yachts Rule (MPY) - Originally applied to ALL displacement and high speed motor yachts in wood, GRP, steel and aluminum up to 200 feet (61m).  In 1995, the scope of this rule was limited to motor yachts between 79 feet and 200 feet (24m - 61m) without any actual changes to the rule. The ABS MPY has proven to be an excellent all-around rule, although it has now effectively been superseded by the 2016 ABS Yachts Rule (see below).    2016 ABS Steel Vessels Rule (SV)- Applies to steel commercial vessels up to 295 feet in length (90m).  Specified by the US CFR for use on steel yachts carrying passengers for hire, whether power or sail.  It is apparent that the US CFR has not yet caught up with the recent publication of the comprehensive 2016 ABS Yachts Rule which applies to private and commercial yachts up to 200 feet (61m ) .    2016 ABS Yacht Rule - Supersedes ALL prior ABS Rules applicable to private and commercial yachts of all types built in any material between 79 feet and 295 feet.  If taken literally, the ABS Yacht Rule replaces both the 2000 ABS MPY Rule and the 1994 ORY Rule.  In the coming years it is likely that the ISO-12215 rules will find their way onto the scene in the US for private yachts under 79 feet.    From the above, it seems the following ABS Rules should be applied: Yachts UNDER 79 Feet (24m) :  Per the above scope limitations, we are left without an ABS Rule that applies to any kind of vessel under 79 feet (24m).  However in consideration of the original scope of the above rules it seems most appropriate to still apply the 1994 ABS ORY rule to sailing yachts and the 2000 ABS MPY rule to motor yachts in the US.   Both rules address steel, aluminum, fiberglass, and plywood construction, and are therefore quite versatile in their application.  For any sailing or motor yacht that is destined for the EU, the applicable ISO-12215 scantling rule will apply.    Yachts OVER 79 Feet (24m) :  Here, the 2016 ABS Yachts Rule will apply to all private yachts, as well as all commercial yachts that carry 12 passengers or less.  Yachts that carry between 13 and 36 PAX are considered 'Passenger Yachts' and must use the ABS Steel Vessels Rules as applicable to the vessel's size.  Since the ABS is considered a 'Notified Body' in the EU, the new ABS Yachts Rule can be used to class any yacht over 79 feet (24m) within the European Union. All yachts carrying passengers must additionally comply with Flag State requirements with regard to safety and stability that apply to commercial yachts (such as the CFR in the US or the UK's MCA LY3 rules for States using the Red Ensign). NOTE :  The ABS Rule for Steel Vessels Under 295 feet (90m) has received vigorous editing by the ABS in recent years, and has consequently grown to nearly absurd proportions in an attempt to cover all manner of steel craft.  In the process it has become an extremely unwieldy tome that is of questionable applicability to any sort of craft under 79 feet (24m).   Even though the US CFR requires using this rule to assess the structure of all commercial vessels carrying passengers, I do not regard the ABS Rule for Steel Vessels Under 295 feet as being at all relevant to any vessel under 79 feet (24m).  This is a case where the Flag State (i.e. the US) imposes a more restrictive rule for commercial yachts.   SCANTLING CALCULATIONS Within all of the above mentioned ABS rules the method for determining scantlings is generally the same, as follows: 1. First a head pressure is calculated for each region of the boat, based on boat size and dimensions. Alloys are then selected, and the allowable yield strength for the chosen alloy is considered in all subsequent calcs. 2. Then a hull plate thickness is selected and verified per the rule, based on experience, boat size, usage, location, etc. 3. With a plate thickness chosen for each region, a long'l stringer spacing is then selected and verified based on what is necessary to support that plate thickness, and based on the location and the resulting head pressure. Then a frame spacing is selected and verified, based usually on what is practical in terms of attachment of the interior and the arrangement of interior spaces (typically double the long'l spacing, or thereabouts, but often more). 4. Once the long'l and transverse spacings have been chosen, the long'l stringer scantlings are selected, calculated and verified based on the location, plate thickness, and the maximum span between frames according to the prescribed minimum Section Modulus. 5. Then the transverse frame and deck beam scantlings are selected and calculated on the basis of being at least twice the depth of the long'l stringers, and verified against the prescribed minimum Section Modulus in the rule, which is calculated according to the local head pressure and the local span, and which considers the local plate thickness. First, a few simple limits apply: Aluminum plate must be at least 5/32 inch thickness as an absolute minimum. Based on vessel size, head pressure and plate location, greater minimum thicknesses may be prescribed. In some cases a credit might be available, based on the aspect ratio or the curvature of the unsupported plate region. In other cases, such as for tanks on commercial vessels, 1/4 inch aluminum plate is the minimum thickness used. Also per the ABS MPY rule, the ratio of depth to thickness for any aluminum flat bar frame members (transverse or long'l) must not be greater than 12:1, or a rider bar or flange must be used. A flat bar flange is also limited to a 12:1 ratio (width to thickness). The depth to thickness ratio of web frames with flanges must not exceed 59:1.  For aluminum, the depth to thickness ratio is adjusted according to a factor based on material strength. The ABS MPY rule allows a region of plate adjacent to each frame member equal to 80 times the thickness of the plate to be included in the Section Modulus calculation, but limited to no more than half the frame member's local spacing on each side of the member. The ABS ORY rule allows a region of plate 100 times the plate thickness to be included in the frame and long'l stringer SM calcs. My own preference is to limit the Section Modulus credit to 60 times the local plating thickness as a maximum, per the Nevins Rule. In any case, this credit assumes the local plate will be attached to the internal member by welding per the ABS calculated welding schedule.   PLATE THICKNESS The hull plating thickness required for ocean-worthy aluminum boats depends on the boat size and on the spacing of the internal framing. For a skiff or pram, 1/8 inch aluminum plate is about as thin as can be welded easily. For larger boats, although the ABS rule allows the use of aluminum plate as thin as 5/32 inch, the minimum thickness I use is 3/16 inch regardless of boat size (except for skiffs and prams). For the hull bottom and topsides, I consider it best to use a minimum of 1/4 inch thickness for boats of from 30 feet to around 45 feet, length on deck, then 5/16 inch up to around 55 feet, then 3/8 inch up to around 100 feet, etc. Keel sides are generally one size greater in thickness. Decks and houses are typically one size lesser in thickness. These are only very general guidelines for minimum thickness. The ideal plate thickness depends on the as-welded strength of the alloy chosen, the type of boat it is used on, the location of the plate, and very much depends on the spacing of the internal framing. If it is desired to make use of a wider frame or longitudinal stiffener spacing by using plate of greater thickness, the ABS calcs will reflect the added strength imparted due to the greater plate thickness. For aluminum, a few special considerations are imposed. Among them is to provide increased plate thickness in way of stress points such as next to the keel, above the propeller, around the rudder post, and in way of any other fittings that will have high stress (cleats, bitts, mast partners, chainplates, windlass, etc.).  Another consideration for aluminum is that plate seams should be located at the point of least stress.  For transverse butt weld seams, that location is 1/4 of the local span in between frames.   TYPICAL FRAMING The required dimensions of the internal transverse and longitudinal framing depends on their location and their span, but also depend on the thickness of plate, as noted above. Using the minimum plate thicknesses outlined above, it is fairly typical for longitudinal stiffeners to be spaced from 12 inches to a maximum of around 18 inches, depending on the plate thickness, location, head pressure, etc. As noted above, it is more or less the case that transverse frames will be spaced approximately twice the long'l spacing. Transverse frames must always be twice the depth of the long'l stiffeners. If the plate is of lesser thickness than outlined above, or if the service is more severe (such as for a high speed vessel's slamming loads), the stiffener spacing may well need to be less than the above spacings. If the plate is of greater thickness, then the stiffeners and frames may be farther apart. One of the excellent benefits of using the ABS rule is that one can freely vary the sizes and spacing of the internal structure according to what is readily available, what is the most simple, and in order to accommodate different build strategies.   EXTRUDED SHAPES On small craft under around 70 feet, for the sake of simplicity it is my preference to use flat bar for internal framing. As a result, the 12:1 depth to thickness ratio limit automatically imposes a minimum thickness for each of the long's and frames. Where it is necessary to exceed that aspect ratio in order to satisfy the minimum required Section Modulus, but a greater thickness is not desired, a rider bar will be used. For example, it is always necessary to use rider bars on floors, since they always exceed the aspect ratio limit. I will use rider bars or flanges for frames if needed, but generally not for long'l stringers. Even though "T" shapes are superior structurally, for the sake of simplicity I prefer to use only flat bar for frames and for long'l stringers. On occasion for fast boats that must be as light as possible, I might specify a "T" shape for a long'l stringer, but not without considering alternate arrangements or closer spacing of flat bar, etc. The available "T" bars are given in a link provided at the end of this article. Those "T" sizes are available from Alaskan Copper, and can therefore be considered , however they may not be readily available to all builders. The Alaskan Copper stock list also shows what they refer to as a "6061 Hull Stiffener" which might also be considered for small boats, but I have not used them. I have seen some applications of American Standard channel for long'l stringers, but not very often. Also, structural angle is used on occasion for long'l stringers, and might even be fairly common on some kinds of commercial boats. I tend not to use any angle whatsoever, mainly because all transverse members are NC cut and will therefore be given a rider bar instead if necessary, and because for long'l stringers angle is not stable in bending since it tends to want to collapse with the open angle inward or outward.  So even if strong, angle is not very "builder-friendly" especially where there is any amount of curvature.  If needed for strength locally, a "T" stiffener would be vastly preferable in those locations. For regions of little or no curvature, say possibly for deck stringers, structural angle might be used more often than I imagine, however even there it requires a rather large cutout in the transverse frame, which either adds complexity in order to weld in a patch, or will otherwise reduce the strength of the transverse frame. I tend not to use "half pipe" sections anywhere except as an entirely external rub-strake at dock level for use as a bumper. It is tempting to make use of half pipe as an external "keel cooler" however for the sake of achieving minimum wetted surface, it is always preferable to locate any cooling channels entirely inside, say in place of an internal stiffener or as part of the keel box. On the other hand, I do make extensive use of "full round" pipe sections, which are located at the intersection of hull and deck, and as trim on the top of bulwarks and around other edges. This is both an aesthetic choice, as well as a functional choice. At the intersection of the deck edge with the hull sides, a full round pipe adds considerable strength, and serves as a robust guard. At the top of a bulwark, a full round pipe provides a visual appeal, as well as a well-rounded edge to better hold paint, and to prevent chafe, etc. In my use, these full rounds are usually specified as "pipe" rather than as "tube" since tube tends to be relatively much less common in North America, therefore tube is less easy to source. Schedule 40 pipe is the most common and the most readily available thickness. For aluminum structures I will sometimes specify schedule 80 pipe – primarily for ease of welding in the smaller diameters. An advantage with pipe is that for any given nominal diameter, it always has the same O.D. regardless of wall thickness, so that threaded pipe fittings will work on any schedule thickness. Butt-weld ends, elbows and tees are available for pipe, and make for excellent terminations and transitions. In the EU, and "down under" the situation is quite the opposite, with metric tube being commonly available, and imperial dimensioned pipe being rather difficult to source. Many builders prefer to use a heavy wall pipe or tube or a solid round rod at all chines. I prefer not to do that because it complicates the welding considerably (double the number of welds along the chine…!). Instead, I prefer to locate the first long'l approximately 3 to 5 inches from the chine corner or plate edge, depending on plate thickness, on both sides of the chine. This stabilizes the weld-zone considerably, improves fairness, and vastly simplifies the assembly and the weld-up. I have not made much use of "I" beams on boats, except as girders on larger craft, however possibly they could be used as compression posts or stanchions. In general I prefer to use pipe or tube for posts and stanchions, especially in locations where they will be used as hand-holds. Although "bulb flats" are available on occasion, I have not them used on small craft, nor would I specify them.  They are used to good effect in larger craft and in military craft.   REVIEW & VERIFICATION My own review process starts with making sure that all structure is simple, practical, easy to build, and has good access for welding and maintenance. I will then verify the proposed structure per the applicable ABS rule. If regions of plate are in doubt, I will verify plate thickness and internal support according to plate theory per local edge fixity. If the vessel is very slender, or is shallow in relation to its length, then the ABS Aluminum Vessels rule requires a global longitudinal strength analysis, based on a calculated minimum Section Modulus for the whole vessel. This would not ordinarily be a factor for vessels under around 60 to 80 feet. Although this may at first look like a very complex calculation, the ABS AV rule uses a fairly simple approach. As noted above, in general it is best to locate transverse plate seams at 1/4 the span between frames - at the location of least stress. It is desirable in all cases to locate plate seams away from other stress points, such as hatch or house corners. In general, all house and hatch corners should have a generous radius. It is generally desirable to reinforce transverse plate seams using "sister" long'ls to span the seam, which also helps to minimize distortion during weld-up.   SOURCES One of the best sources of supply for aluminum alloy shapes and plate on the US West Coast is Alaskan Copper ( www.alaskancopper.com ). And... any of the ABS rules mentioned here can be downloaded for free at www.eagle.org , in the Marine section. Probably the best general guide to structure for metal boats is Tom Colvin's excellent book "Steel Boatbuilding" which, even though aimed at building cruising yachts in steel, is entirely applicable to building similar types of boats in aluminum. I find the examples of typical boat structure that Tom Colvin has offered to be very simple and extremely practical.   PARTING SHOTS It should be rather evident from the above that I do not subscribe to the so-called "frameless" approach to metal boat building. For a discussion of the merits of the so-called "frameless" approach, please see my article on Metal Boat Framing . On the other hand, I do strongly favor the use of increased plate thickness in order to minimize the internal framing wherever it is practical to do so. Further, there is no special requirement that dictates whether the frames or the plate will be erected first. For a discussion of various methods of metal boat construction, please see my article on Metal Boat Building Methods . The approach of using increased plate thickness in order to limit internal framing is sometimes referred to as the "Strongall" system, which a company in France claims to have "invented." This approach definitely saves labor (and therefore costs) and vastly improves hull fairness. Despite those advantages, increased plate thickness will certainly result in a heavier structure and a higher materials cost. This illustrates one of the biggest benefits of using the ABS rule, which is not a rigidly "prescribed" tabular rule (as is for example the British Lloyds rule). In other words, when using a "calculated" approach to boat structure as is inherent in the ABS rules, we have always had the option to freely vary the internal structure and plate thickness, for example to increase plate thickness in order to realize benefits in terms of simplicity of a boat's internal structure. Come to think of it, this was actually not "invented" in France after all… it is merely a practical approach to metal boat building!   Other Articles on Boat Structure Metal Boats for Blue Water | Aluminum vs Steel | Steel Boats | Aluminum for Boats Metal Boat Framing | Metal Boat Building Methods | Metal Boat Welding Sequence | Designing Metal Boat Structure Composites for Boats | The Evolution of a Wooden Sailing Type   Kasten Marine Design, Inc. Professional Memberships Member Royal Institution of Naval Architects Member Society of Naval Architects and Marine Engineers Member Society of Boat and Yacht Designers Member Metal Boat Society Member American Boat and Yacht Council

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Aluminum Boat Hull Designs - The Why...

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I'm driving my first aluminum boat. I've ridden on a few. I've been in fiberglass boats mostly and always noticed the pound sand crowd when they go by and you hear that boat slam repeatedly. Never wanted to sign up for that. Fiberglass is for a cadillac ride. That extension on the Boulton bow is for spray control? And why do manufacturers make cabin space but not enough deck space? Our 28' EdWing does not pound and it is not the typical aluminum boat. Maybe it's just heavier so it does not lift up very high on the up wave. There is no bilge to worry about. 6 inch reverse chines 3/4 the boat length seem to throw water out and away most of the time. If we are taking spray it is really nasty that day. We have .250" sides, transom, and bottom with 1/3 section of 3" sched 40 pipe rub rails welded on, 1 on each side plus a full pipe rail on the gunnel. The reverse chines are nice ... this boat handles crossed up water with little effort. Back aft the motor floatation is just a solid continuation of the hull, no welded on box to crack at the welds. Walk around the whole boat and take your fish with you, only the engine will get in the way. The huge deck means I don't have to worry about crowding fishermen with a half tote, crab or shrimp gear. I only see a few, mostly custom shops building this design. Crozier, EdWing, Pacific Skiff. Ed designed this hull for the CR bar. And you see it on almost every one of his smaller boats. We park three of them in a row at our storage spot and you can see the similarities. The hull shape and contours are the same other than length. Must be something to it.  

I do recall reading in either Gerr’s book or it might have been Pollard’s that .250bottom on anything under 25’ boats was overkill. Probably the biggest gain you get on a small boat with thicker aluminum is weight so you get a better ride, but you sacrifice fuel economy and payload. Its a compromise 😀 .125 is usually the minimum thickness because of welding and the heat affected area which results in strength loss. .250 sides is pretty beefy there Han  

Boy I could talk hours about this topic. To start off, everything is an opinion. Also, you have to remember that everything is compromise and there's more than 1 way to skin a cat. The main compromise being stability at rest and on the troll versus when on plane, in my opinion. Very few boats are able to nail both. Reverse chines... more stable at rest 95% of the time. On plane, it depends on the boat. Some boats don't need the extra lift, some don't. Comes down to bottom loading .. ie weight vs wetted surface. Too much stern lift can cause broaching and bow steering. Too little and the boat rides bow high. The balance point is getting the waves to hit the steepest deadrise area of the keel. Boats with a deep forefoot in the bow and a lot of deadrise are the most delicate with balance. But the boats that nail it ride extremely well. Comes down to knowing the design of the boat, weight balance, intended speed, etc. For an aluminum boat, i'd argue .250" bottom is never overkill. Have seen a couple boats running 3/8" or keel doublers too. All aluminum offshore boats can benefit from more weight down low to help balance. The bent shape you see in sides act as ribs and add stiffness in lightweight material.  

mitch184 said: The bent shape you see in sides act as ribs and add stiffness in lightweight material. Click to expand...

Hopefully jonathan Lawrence chimes in. He’s a wealth of good info on boat design and always willing to answer these questions.  

You beat me too it! Johnathan is very sharp on this stuff and is a wealth of information in the boating industry. I can attest there Raider design is stout and stable. I have ridden or driven Raider coastal or sea raider designs since 2006 I believe it was, when a cousin got his first boat. I have had my coastal since 2018. They don't need to be babied.  

Wonder if he worked for hewes for a bit? Strikingly similar designs.  

The founder of Raider worked for Hewes.  

My built in 2018 Raider 2496 has a welded on rub rail….  

Jeb said: While we are at it...let's talk about hull extensions. Why do some boat designers go with a full hull 'width' extension/offshore design and some go with a partial (what I mean by partial is, it does not go the entire width of the hull; the extension pod only goes partial width across.) For example, look at the back of this offshore Weldcraft. The hull extension does not go the entire width. It would seem that you get better buoyancy with the wider extension. On the other-hand, this Raider almost goes the entire width of the hull. Click to expand...

A few thoughts.... * Anglers are very susceptible to fashion and trends. Boat manufacturers are acutely aware of this, so they're constantly trying to build boats with the features and looks that are currently in style. For example, big motors and high speed are in fashion now. It's become conventional wisdom to put the biggest possible motor on a given boat, even though the downsides often outweigh the upsides for most applications. * Shipping costs are significant, so boats are sometimes designed to stack neatly on trucks for cheap transport * Aluminum cannot be formed into compound curves, hence the shape of aluminum boats will always be on the boxy side. Fiberglass and wood-planked boats can be formed into any shape and that lets designers truly have their free hand in designing for efficiency, seaworthiness and beauty. Aluminum designs are always constrained by the inability to bend sheet aluminum in more than one direction (like a sheet of paper) * Most aluminum boats are pretty darn good these days, and I don't get too excited about Brand X over Brand Y, or about various types of joints, or hull thickness. I don't see many boats breaking or falling apart, and if they do, it's usually a maintenance problem. * Wiring and electronics installation seems to be a weak point with alumunim boats these days.  

I grew up fixing old boats with my Dad who was compulsive about doing things the right way. I have been lucky enough to fish on a lot of different guys boats. The biggest problems I have seen on aluminum boats are. Corrosion issues associated with paint or dissimilar metals in contact. Crappy wiring jobs that will result in corrosion. Fuel systems setups that are just goofy. These are the things I would be most concerned about when purchasing a new boat. Some of the factory wiring and fuel jobs make me wonder if the person responsible for them is competent enough to be out in the world unsupervised.... I think most of the common PNW brands have very similar ride quality and hull characteristics. Pacific skiff and Ironwood are putting out hulls that are fairly different from the others. Never ridden on an Ed Wing.  

Ed wings are tough heavily built boats. My 21 footer is 3/16 with a quarter inch bottom and basically the style of a working man’s vessel. the guy who has to go to work every day. whether the ocean is nice or snotty drives a boat shaped like mine. I’m not getting there fast, but I’m getting there. Scuppers out the back and six sealed welded air chambers underneath add mental comfort to your ride. I will add that we ride for comfort. I never try to go faster than the ocean dictates I don’t wanna pound across the ocean. I want a nice mellow ride. when we get there we know what to do.  

I have been doing lots of research into this as well lately. Im planning on building my own boat, using either a specmar design or a Conrad yachts. After fishing on a couple of walk around pilothouse boats Im convinced that, that is the ultimate fishing boat for our waters. I will either build a pilothouse or a CC with full windshield and hardtop with curtains all the way around. Ive also read Polards book and have everything I need to start minus the kit itself. I have a couple projects to wrap up first then I will be getting started. I will definitely make a build thread as I progress through it.  

messmaker said: I will definitely make a build thread as I progress through it. Click to expand...

Oh man... this is right up my alley without enough time to dive into most of it. I'll chip away at things as much as I can but the best blanketed answer to all of your questions is taught in naval architecture in the beginning of your course work.. There is not one single universal hull design that is the best in all types of water. It's all a give and take. Most manufactures are trying their best to drive down man hours. You have to think of it like a business where a few things are true. A boat manufacture is selling two things, materials (COG's) and Direct Labor. Very similar to a service shop actually. You're managing your material costs which are relatively set, but your direct labor revenue (effective labor rate) or billable efficiency is what you have to manage. This is where your lean manufacturing principles come into play. We all think of Lean MFG as good, and it really is.. but it can also be bad. Some builders design boats with lean as a paramount and not a consideration, meaning they will not "overbuild" the boat but instead they will build it to an adequate enough point that their user needs and the design of their boat. What is adequate and overbuilt? That's all subjective. When I say overbuilt, I may be comparing one build to what would be considered a standard build in the industry. This is also why some companies classify their boats as "Inshore", "Lake", etc... Their warranty will generally be subjected to your use. If you buy a 20' 66" bottom .160" hull plate brand XY or Z and take it offshore 50 miles for albacore and the hull cracks.. well. No kidding. We've all seen the guys on Facebook talk about how their boat built like that does great offshore.. Yet no experienced and honest professional would be surprised by that happening and the mfg that built that boat likely won't warranty it cause it wasn't designed for that kind of water and if it was.. they lack common sense. The salesmen at Dealer X isn't going to tell you this, you would have to be very specific with a builder to see if they would warranty something like this in that use. What I'm saying here is Yes. a lot of things with manufactures are done for the bare minimum to make it just good enough. Not always is it that a .160" hull plate that's going to crack in big water... that's relatively rare cause most users don't run offshore in a boat like that.. but the external chine weld out would be one good example of this. Most buyers are fishing freshwater or a mix so it's less of an important item. Where we choose to weld it out, a few things come to play. Heat... if I had .125" sides on the hull and did a full chine weldout on the outside of the extrusion then it would oil can like a frying pan that got too hot. This leads us to do a minimum hull side of .160" to mitigate that. So the decision to add one full length weld has a factor of the use of thicker plate so as we make this decision we discuss it's relevance to our goals in the design of our boats, which is big water ocean use.. so the weight is a good thing. If I was building a boat for lake fishing and running around Detroit.. it's VERY unneeded. If you're fishing offshore in the ocean, that's the design paradigm we build within so the decision to an external chine weldout is a must and the additional changes it requires all benefit the end user so.. we do it. The added bow plates like that Boulton is call Bulwarks and is common in big commercial boats. To get the bow to hook up it takes some force and manipulation that can create allot of variance in each bow deck area if not done consistently. Bulwarks is a quick and easy way to design in a little better seakeeping. Duckworth does this as well on their pac pro and offshore products, it's just built into the side sheet. Having a gunwale profile that is flat will shave 20-30 hours off of a build when assembling a cabin and fitting a cabin to a consistent radius that always fit, requires a complete change in build process or a large investment in fixtures to make things more replaceable. This is all easily fixed with a flat gunwale so why do the former? As it pertains to welded rub rails.. they're 100% personal preference and a look thing. They definitely make a boat stiffer and stronger.. but the chance they line up perfectly on a dock is a crap shoot. If you launch 10 different placed you'll have 10 different dock heights. They just look bad ass and that may culturally change in time. For now, most everyone wants them and two of them per side if they can. The rolled sides or bends in the sides stiffen the plate. This is a great alternative to heavier plate. I've actually thought about doing this and one day I may but that's a very VERY unlikely chance. It is vastly more efficient to put bends in the sides rather than weld on internal structure. If you look at Weldcraft/Duckworth on a lot of their smaller boats without the formed sides, they have a angled stiffener with 1" feet on top and bottom, you'll actually find that they glue those on with what I assume is some sort of panel bond like a Lord Fusor type material. This is done to give the sides the stiffness needed without any added heat. It also can likely be applied by an entry level tech vs a higher tiered welder. (To be clear, I'm not knocking the panel bond, it's actually really smart and a number of years ago I did some destructive testing on sheets of aluminum panel bonded with Lord Fusor. I would argue that one could likely build an entire boat with it and it be stronger than a welded product as you prevent heat fatigue. When talking about this boat and that boat with hull plate and structure and.... How many 10 year old boats have under 500hrs on them? MOST! so the idea of "oh all brands are good, how often do you see cracks.. or hull issues".. is kinda silly. Cause you do see them often but when the boat is 15-20 years old and now finally has around 500-700hrs on it. I feel like I know my client fairly well, we don't sell many boats to guys that put 100hrs on their boat in 4 years. A lot of our clients use the ever living life out of them, I myself put 350hrs on my personal boat last year between June and September and I live 10hrs from the ocean. It's a lifestyle for our customers and myself which drives one to build things in a way that will last under heavy and dedicated use. It's amazing to me how some guys, guides even, that will promote boat brands that literally exclude guide and lodge use from their warranty OR as I recently read on a competitors warranty... companies that define "Lifetime" as 20 years... so they warranty the boat for 20 years, not a lifetime.. but that's in the details of the warranty.. not what's marketed. on top of that, they exclude the guide from there warranty... The limitations to their warranty period is generally not a random number, that's where they start to see hull issues more readily. If you're fishing in a lake, not really an issue but in the ocean, we ask a lot of these boats so being critical about build structure, hull design, plate thickness really does matter. This is an example of building a product that is "good enough" within the means of the lean principles in their engineering team.. What no one knows is what is the baseline? What is their experience? There are rules and regulations we follow for stability and design principles but really and truly there is no crash test standards, there is no performance metrics we're held accountable to, its literally experience that we build them from and whomever is involved in the designs of the boats will base the designs through the paradigm of their experience. Hopefully my opinion will answer some questions, I know not everyone will agree with me but that's what makes boat building so fun. We all build boats based on our professional experiences but what separates some builders is the personal experience in using the boat that really separates them. I'm not talking about taking a 10min WOT joy ride on the Willamette damaging the cylinder walls of a brand new 300hp outboard.. I'm talking about spending some time west of the 125 line or knowing what it's like to reel 3lb's of lead from 750' on the edge of the canyon and all the things the boat needs to do to make it more efficient and better. I enjoy this stuff so I look forward to this discussion continuing.  

KMG-Raider said: . What is adequate and overbuilt? That's all subjective. When I say overbuilt, I may be comparing one build to what would be considered a standard build in the industry. This is also why some companies classify their boats as "Inshore", "Lake", etc... Their warranty will generally be subjected to your use. If you buy a 20' 66" bottom .160" hull plate brand XY or Z and take it offshore 50 miles for albacore and the hull cracks.. well. No kidding. We've all seen the guys on Facebook talk about how their boat built like that does great offshore.. Yet no experienced and honest professional would be surprised by that happening and the mfg that built that boat likely won't warranty it cause it wasn't designed for that kind of water and if it was.. they lack common sense. The salesmen at Dealer X isn't going to tell you this, you would have to be very specific with a builder to see if they would warranty something like this in that use. Click to expand...

Building boats to make money has a viewpoint thanks for sharing it. I'm looking at it from a different perspective. Often I specify eqiupment and usually there is considerable reserve capacity or ability required. You may never need to push that emergency diesel generator to 100 KW but it will last longer and perform better loaded to 2/3 of that capacity. Taking a longer view includes considering the durability and repairability of a thing. We bought a workboat. We will use it hard with confidence. Personally I cannot imagine owning a 15 year old boat with only 700 hours on it. I'm at 550 on the main after three seasons. 200 - 250 a year is more normal for us and I have had way too much summer time the last few seasons wrapped up in things not fishing.  

I’ve got one that’s 25 years old a little over 6200 hours second motor if you’re not gonna use it. Buy a picture of a real nice one and hang it on your wall  

I don't necessarily disagree but I also know how life can get. I've had years I can log 500hrs offshore and others I can log 10 but it's the thing I do, I don't ski, I don't travel, I don't golf... I fish and I hunt but I mostly fish. That's not the case for most people. I think a lot of people like having a boat and having control of their recreational time, have the money to have said equipment and want to use it when they please which may only be 75hrs a year.  

Jeb said: Although this isn't necessarily 'hull design', but why a half swim step option on some models of boats? For example, here is a NorthRiver Seahawk with a full swim step with the kicker bracket on the port side. View attachment 1038246 . Here is the same year model...and its a half step. View attachment 1038247 The only thing I can think of is that maybe the kicker bracket is mounted a little closer to the stern so if you want to manually steer the kicker with the tiller...you can do that with this half step model, while the full step model is farther back and so you have to remote steer to make it useful? Do any of the swim step designs add any more strength to the stern area or is it really inconsequential? Click to expand...

Good points Jeb! I believe Raiders original owner did the full width extention to improve the ride and stability of the boat. (The Longer rides Better concept) It Also ads more displacment for the offshore bracket if I'm not mistaken. Seems like I remember hearing something like this years and years ago when Mike/Raider Boats split off from Hewscraft.  

Reel fortunate said: Good points Jeb! I believe Raiders original owner did the full width extention to improve the ride and stability of the boat. (The Longer rides Better concept) It Also ads more displacment for the offshore bracket if I'm not mistaken. Seems like I remember hearing something like this years and years ago when Mike/Raider Boats split off from Hewscraft. Click to expand...

Jonathan, its interesting your comment about 'trial and error'. We've all heard about "this or that boat had issues in the 90's with cracked welds", and "this boat had issues with their 'offshore, hull extension with cracked welds in the early 2000 period, but after 2006 models they went to stringers that extended out the back for more structural support", etc, etc, etc. You can plug in a manufacture name and a year in those and other sentences...but the point being the same, it was indeed trial and error and many of them will readily admit it. The issue I've had on boats in the past was- they are fine on the river or on a lake - but the ocean will truly tell you where the weak points are in short order. I've had some aluminum boats in years past (I'm not mentioning names), but after a few years the hull takes a beating and you start to see major stress marks, fatigue areas and then failure. The amount of energy the hull has to take when exposed to waves is ridiculously high. It looks nice for the first couple of years...and then you begin to see every single longitudinal, stringer and transverse bulkhead showing through the hull with a slight bend of the hull. Is the boat going to sink? Probably not, but you definitely can tell the hull is taking a beating and it shows. In the mid-90's I had one hull that used wood in the transom sandwiched between the aluminum material. Well...some how, some where...that wood absorbed water and in time it made for a weak transom. I'm sure they don't make their transom's with wood sandwiched between the aluminum now days...so I'm sure they changed their design. But hey...was that trial and error? I would say yes. (BTW, I hope no one is still building that way) On a similar note, several years ago, when I added a bow mount Minn Kota on the front of my Weldcraft, I didn't think about the amount of force/torque applied to the mating surface, nor to the aluminum sheet welded to the rub rail on the front where the anchor nest was mounted. After about 5 years...it cracked the extrusion/rubrail and the sheet material. I had to grind and weld that crack and then add additional structural support under the bow to handle the stress. Trial and error? Yes...because many folks didn't have these mounted on aluminum boats with long 72+" shafts and using them in heavy current, heavy wind, even with large swells on a heavy boat on the Pacific. It was mostly bass boats in the mid-west with the occasional Floridian glass boat using it offshore. There is much practical knowledge gained from 'lessons learned' that you can't always foresee. Its really nice to hear you guys fish and stress test your boats in the waters we fish. That speaks highly of your design and what practical changes you make in the hull design.  

Smokercraft still sandwiches wood in the transom at least on the pro lodge.. but when you buy something like a smoker you kinda except it’s not a top of the line design lol.  

I think that is why Bouton Boats were well built. I understand Mike has a Marine engineering degree, and grew up around building aluminum boats. My 1991 Jetcraft is a Mike Boulton designed boat. I think his dad was with Alumaweld when he and Bruce Wassen left to start Jetcraft. So Mike had both technical training and trial and error training. Had only two cracks on my hull. One a bad weld on a floor support and originally had an OMC kicker bracket and after 10 years cracked the transom.  

It’s all about cost and brand name. My 24 foot Ocean King has 1/4 inch bottom sheeting and aluminum I beams under the forward deck. I wondered why the stout construction and was told some boats were built for military use, it weights in at just under 5,000 lbs.  

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Thickness of aluminum cat hulls

Discussion in ' Materials ' started by JonathanCole , Aug 18, 2005 .

JonathanCole imagineer

If I am using type 5052 H32 Aluminium/magnesium alloy to build catamaran hulls, is .125 thickness adequate for a robust hull, assuming all curves, and bulkheads at a minimum of 5 feet on center? Also, can this material endure without coating it? Also posted on metal boatbuilding forum.  

CDBarry Senior Member

What do you scantling calculations tell you?  

I can't find a precise definition for "scantlings". Where's that BoatDesign.net glossary? Can you explain scantlings?  

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D'ARTOIS Senior Member

For your purposes Jonathan, 4mm minimal thickness is required, 5 mm would be better. The hulls are stiffened in the longitudinal way sufficiently by the top mounting bracket and the long rubstrake along the hull. Since those hulls have to carry only weight distributed over the whol length, more reinforcements are not required save for some bulkheads to keep you afloat at a collision. And there have been taken provisions for.  

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Hull thickness

• Thread starter 1960 yellowboat
• Start date Aug 3, 2019

Help Support TinBoats.net:

1960 yellowboat, well-known member.

• Aug 3, 2019

What is considered to be a good material thickness on an aluminum semi vee? My Richline Challenger is .067 gauge.  

Depends on lenth ,,,  

.080 is considered "decent" on a lot of the 15' duck boats, with .100 or .125 preferred, but they are going to be obviously heavier-and that means slower speed. Mine is .100 (1548).  

RaisedByWolves

• Aug 4, 2019

DaleH said: Depends on lenth ,,, Click to expand...

Active member

• Aug 8, 2019

It's interesting how much this has changed over the years. I bought an aluminum boat in 1977 that was .064, and that wasn't unusual. The next one I bought a few years later was .072 and I remember the salesman talked about the hull thickness as a great selling point. I have been researching boats lately and planning to buy one soon, and it seems like most of the bass type boats are .100. I guess thicker is better, but I never had a problem with the hulls on any of my aluminums except for a couple of really small ones that I abused on creek rocks. BTW, I kept running across this site when researching boats, so I decided to join. Thanks for all the great info here.  

Gosh, I had no idea what the hull thickness is for my boat. I suspected it wasn't super thick because I don't think my boat is very heavy for an 18' windshield walkthrough. I looked up the spec's and it comes in at .080 on bottom and sides. Well, now that I know I"m not sure what I'll do with the info. Haha  

• Aug 9, 2019

What are you going to do with it? If you are just going lake fishing then the .07 thickness is just fine, if you want a jet boat and plan on running rocky rivers then the thicker the better. Thicker usually means heavier.  

Thicker is always better. It's heavier, but if you're trailering the boat, that's not as much of a concern as it'd be if you was throwing the boat in the back of the truck like I used to do. That's when lightweight tin foil boats are nice to have--at least until you run into a barely submerged cypress tree stump or knee. The difference between a .100 jon and a .063 jon is evident as you're running across the lake running a tiller steer motor with any appreciable chop. With thin material you can watch the front of the boat flex. With the thicker stuff, not so much. Also most riveted boats are thinner material because it takes less material/money to build the boat. It's more flexible which over a long period of time and/or rough water operation will tend to loosen the rivets.  

Are you planning on any rock crushing? Lake boats can be built lighter than river boats.  

• Aug 11, 2019

Gets rough on the lake sometimes too. Hunting out of a boat is also a consideration for some (though I do not hunt-at least not from the boat). Once you've been in a thick welded hull, you won't want to set foot in a tin-foil built jon again. Trust me. It's not quite as easy to rivet a thicker hull as it is on a thin one (like .063). But you don't have to, most of the thicker hulls are welded. They're welded because it's easier, safer, lasts longer, and MUCH stronger. There is a price difference, yes. If it's in the budget, spring for the thicker hull. I understand if it's not affordable--I've been in that situation. Resale on a welded thicker material hull is a LOT higher than a riveted tinfoil hull. Either will float, or they should anyway. After a few years the difference becomes obvious. You'd notice the difference right away if you nave never had a welded boat which was my experience.  

• Aug 13, 2019

.1875 or .250, preferably 5086 as well.  

MacCTD said: .1875 or .250, preferably 5086 as well. Click to expand...

turbotodd said: Gets rough on the lake sometimes too. Click to expand...

• Aug 14, 2019

LDUBS said: MacCTD said: .1875 or .250, preferably 5086 as well. Click to expand...

BigTerp said: LDUBS said: MacCTD said: .1875 or .250, preferably 5086 as well. Click to expand...

MacCTD said: BigTerp said: LDUBS said: 1/4" is getting pretty thick & heavy. I could see it for a work boat. Way beyond what I need in the lakes I frequent. Click to expand...

• Aug 15, 2019

LDUBS said: MacCTD said: I have a 19' skiff with .250 bottom and .1875 sides, it is still a pretty light boat and goes well with a Honda 90, very tough, while it may be overkill for some applications given the choice I would take overkill every time. Click to expand...

LDUBS said: MacCTD said: BigTerp said: Yeah, .250 is way overkill. Guys around here that build custom river jet boats use .190 at the most. Click to expand...

• Aug 16, 2019

MacCTD, that is a bruiser of a boat. The skin on my 18' walk-thru is no where near what you have on the bottom. My dry hull wt is only 750#. Bad chop, I slow way down. Too hard on the . . uh. . teeth. Yeah that's it, teeth. Haha  

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Significant difference in .80 and .100 hull?

• Thread starter Bushy99
• Start date May 6, 2010

Seaman Apprentice

• May 6, 2010

I realize that the hull is 20 percent thicker. Are there any real advantages to this? Would the .80 be ok? -Blake  

bob johnson

Rear admiral.

Bushy99 said: I realize that the hull is 20 percent thicker. Are there any real advantages to this? Would the .80 be ok? -Blake Click to expand...

Lieutenant Commander

Re: Significant difference in .80 and .100 hull? That must be a typo---.100(1/10th inch) versus .800(4/5ths inch) is over 3/4ths inch difference. You must mean .080 versus .100--or .020 difference.  

BaileysBoat

Senior chief petty officer.

Re: Significant difference in .80 and .100 hull? Actually, a .100 hull is 25% thicker. A lot of welded aluminum boats are .125, .185 and .250 at the transom.  

Re: Significant difference in .80 and .100 hull? You are correct on the 25 percent. I always sucked at math. The boats I am referring to are the Xpress welded and the Lowe boats. I was eyeing a 15 foot Xpress that dropped down to 0.80. The 16 foot Xpress is 0.100.  

BaileysBoat said: Actually, a .100 hull is 25% thicker. A lot of welded aluminum boats are .125, .185 and .250 at the transom. Click to expand...

Supreme Mariner

Re: Significant difference in .80 and .100 hull? The number is .080 not 0.80 or .80. Both .8 and 0.8 are the same (over 3/4 inch thick).  

Silvertip said: The number is .080 not 0.80 or .80. Both .8 and 0.8 are the same (over 3/4 inch thick). Click to expand...

26aftcab454

26aftcab454 said: my 1957 LoneStar El Dorado with a 1994 115 Evinrude-is .100 and still getting the job done- 53 years from now how is your boat gonna be holding up??? Click to expand...

180shabah said: see if anybody is listening this time.... Click to expand...

Bushy99 said: That's great. Do you think being .020 thicker made a huge difference? Click to expand...

Re: Significant difference in .80 and .100 hull? Still undecided between riveted and welded as well. I'm concerned about the seems on a welded hull.  

Re: Significant difference in .80 and .100 hull? I have two Aluminum boats a 1967 14 foot Klamath Delux with rivets and it leaks at many rivets. The one that I can get to I have tightened up and they no longer leak. The ones under seats and the like still leak. In a days fishing will get about 1/2 inch of water. On a hot Sunny California day will be more like 1/4 inch. The hull is thin .060 and it weighs 167 pounds with no motor. The Other boat is a 21 foot Crestliner welded boat and has never leaked a drop. The hull bottom is .080 and the transom is .125. Dry weight with a 3.0L 181 CI 4 cylinder I/O 140 HP is 2800 pounds. For me I think .080 and .100 are a big difference. For inland lakes and small rivers the .080 should be fine. Makes a bit difference if your loading it on top of a truck and carring it up the levey. If You have a trailer go with the extra cost of the .100 and a larger motor. The thicker hull less likely to form a hook in the bottom. Stringer system makes even more difference.  

• May 7, 2010

Re: Significant difference in .80 and .100 hull? First of all. Thanks to everyone for their input. I didn't think about rivets leaking under bence seats. That is a really good point. Most of what I have read about riveted boats is that the leaks are easily fixed. Rivets under a bench seat would be near impossible to fix I assume. Anyone else had experience with this? Obviously there is a large cost difference in the 0.80 and the 0.100, close to a thousand dollars. The boat will be used in rivers mostly. Both the 0.080 and 0.100 are rated for my 40 HP.  

Fleet Admiral

Re: Significant difference in .80 and .100 hull? Last year i replaced an old Sea Nymph 0.080" with a 0.100" Starcraft. Big difference in sound, ridgidity, etc. Of course, its probably a better boat too. I would never own one smaller than 0.100" again. JMO.  

Re: Significant difference in .80 and .100 hull? Thanks for the opinion. Anyone else?  

Petty Officer 3rd Class

Bushy99 said: First of all. Thanks to everyone for their input. I didn't think about rivets leaking under bence seats. That is a really good point. Most of what I have read about riveted boats is that the leaks are easily fixed. Rivets under a bench seat would be near impossible to fix I assume. Anyone else had experience with this? Obviously there is a large cost difference in the 0.080 and the 0.0100, close to a thousand dollars. The boat will be used in rivers mostly. Both the 0.080 and 0.0100 are rated for my 40 HP. Click to expand...

Re: Significant difference in .80 and .100 hull? Probably going with a Lowe Roughneck at 0.100.  

Re: Significant difference in .80 and .100 hull? I have run an .080 F&F 1652 for several years, all duck hunting. I purposly ordered the boat .080 due to the weight difference. It is an all welded boat. I am using a 25 merc 2 stroke on it. It will carry and insane amount of weight into shallow water areas (4 to 12 inches) and it is easy to drag over levys, logs, stumps, etc. Check the difference in weight of the two and you will find that the .100 boat is carrying another "person" all the time. I do not run mine on any large or rough water though. If this were the case I would probably want the thicker hull.