Gemini Owners Resources
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Gemini 105M & 105MC Catamaran Engine Repower / Replacement
Boat type: sailboat, repower specifications, loa: 33.5 ft, lwl: 31.75 ft, displacement: 8,000 lb. (dry), builder: performance cruising inc. (usa).
The Gemini 105M and 105MC started life as a complete overhaul of the previous 3 generations of Geminis from the ground up. Both 105s are the same dimensionally but the 105MC has a taller mast (1 ft) and a sizeable increase (30%) in sail area to 340 square feet. Headroom was also increased slightly in the cockpit of the MC version.
Related Models
Gemini 105M & 105MC
Most Geminis 105M and 105MCs were originally powered with Westerbeke Diesel W30B3 3 cylinder engine (27 hp) connected to a Sillette Sonic Drive with a 16” 3 blade prop. The drive leg is no longer in production but some replacement parts are still available. Fortunately, the drive leg can be tilted enough to be completely out of the water when not in use.
Repower Recommendations
The Beta 25 or the Beta 30 are solid options for replacing the old westerbeke. The Beta 25 is preferred as it is slightly smaller and allows for better access to the front of the engine. The Beta 30 will fit in the space but access to the front of the engine is very limited so it can be challenging to replace the sea water impeller. The Geminis are relatively light catamarans so the Beta 25 will easily push the vessel to hull speed. Some customers prefer the additional power of the Beta 30 and feel the reduced access is worth the tradeoff. The standard 16” 3 blade prop on the Sonic drive is plenty for either engine.
Installation Considerations – Thing to Know
- Our standard engine mounts match up very close to the Westerbeke engine set up. In most cases the Beta engine will need to be shimmed up by about ½” to ¾” to line up with the sonic drive flange.
- In most cases a longer than usual engine harness is needed. Gemini catamaran wiring can be challenging to access and run. Most repowers run the harness to the starboard hull, up and then back to port to the helm station. A 20 – 24 ft harness is needed.
- Customers typically opt to use our full Instrumentation panel (C-Panel) in lieu of our standard ABV Panel.
- We can also provide a new flexible coupling or refurbish the existing coupling to mate the Beta Engine/Transmission to the Sonic Drive.
- The standard exhaust system can be used given the location of the water lift muffler. No need to replace expensive exhaust components.
Key Search Terms: Gemini Cat, Gemini 34, Gemini 3400, 105 MC, 105-MC, 105 M, 105-M, Sonic Drive, Sillette Drive, Gemini 3400, Westerbeke W30, Westerbeke W30b3, Repower Gemini, Gemini Catamaran, Westerbeke repower
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How Do I Replace My Steering On A Gemini Catamaran
These are the instructions that were produced and distributed by Performance Cruising on how to replace mechanical boat steering on a Gemini Catamaran. These instructions are a step by step process on how it is performed. Also included you will find what parts you need based on your model and hull ID and basic tools needed. Since these instructions were introduced we have put together the complete boat steering kits containing all of the correct parts, in one box, that will get your project completed but do not include the tools required. If you go here you can view all of the kits as well as individual parts we offer for your replacement steering. If you prefer you can also download these instructions here.
Performance Cruising Inc. Gemini 105Mc How-To Series
Installing Replacement Steering Cables Version 1.5 – May 2003
Before getting started, thoroughly read the following instructions and review the suggested tools, materials, photos, and illustrations. Replacing the steering cables should take approximately 4 hours.
Replacement parts and complete steering kits can be ordered through www.marinesteering.net located in Arizona. Gemini hull numbers greater than 775 use the new Uflex Quick Connect system which enable replacing a single cable. Boats older than 775 use the older system and require upgrading the helm and both steering cables. If your hull number is within the range of 770 to 775 – check to see which cables you have before ordering.
The parts list and tools are listed below.
The two main components that never change are the helm and bezel kit.
1. #X34 – Bezel 90° Mount Steering Box
2. #T72FC – Dual Rotary Steering Helm
The next parts you will need are the steer ing cables which will vary based on model hull ID numbers listed above. You can choose the correct lengths below. All M66 replacement steering cables come with quick connect ends. So if you have a helm that is threaded vs a quick connect, then you should be replacing your helm as well or you can purchase the complete kit which includes helm, bezel and steering cables. See the models listed below.
105Mc Series Gemini:
3. Part #M66X19 – “Ultraflex”19’ steering cable (port)
4. Part #M66X14 – “Ultraflex” 14’ steering cable (starboard)
3400 and 105m Series Gemini:
5. Part #M66X18 - “Ultraflex” 18’ steering cable (port)
6. Part #M66X15 – “Ultraflex” 15’ steering cable (starboard)
Gemini models without transom steps:
7. Part #M66X17 - “Ultraflex” 17’ steering cable (port)
8. Part #M66X13 – “Ultraflex” 13’ steering cable (starboard)
Last is the tools required. These are the tools that were suggested when the instructions were produced and will complete the job for you. You may have an easier way with your tools, but we are just providing you with a reference.
Tools Required:
9. (1) Pair large vice grips
10. (1) Vise
11. (1) Felt-tip marker
12. (1) Adjustable wrench
13. (1) Standard screwdriver
14. (1) Phillips-head screwdriver
15. (1) Tape Measure
Let's get started on this project starting with step one.
1. Remove old steering cables by first disconnecting the cables from the rudder assembly. Remove lock nuts and washers.
2. You will need to remove the inside access panels in both of the aft cabins to pull through the old steering cables. After removing the cover panels, you can begin to pull the cables through from each aft cabin. See Photo “M” In step 18 of access panel removed.
3. You will need to disconnect the refrigerator and move it forward to access the back of the steering box. After you have access, disconnect the steering cables from the steering box assembly.
4. Unpack the new steering cables and box.
5. Start assembling the new steering system by inserting the longer cable into the left side of the steering box. Use the vice grips to turn the rod clockwise and thread the cable through all the way as shown in the photo “B”.
6. Flip assembly over and insert into vice to stabilize the box as shown in photo “C”.
7. Take the cover plate off by taking out the (4) four screws and then use a flat-head screwdriver to gentry pry open the plate covering the internal gears as shown in photo “D”. Be sure not to disturb the position of the spindles while removing the plate. Simply pry open and gently lift straight up.
8. Use the marker to make a line on the plate indicating “center” as shown in photo “E”. Make a second line exactly 1 1/4” down from the first mark as shown in photo “E”. The mark should be extend from the outside housing of the plate to the inside wheel.
9. Place the plate in the vice as shown in photo “F” and turn the inside wheel counter-clockwise to the 1 ¼” mark on the outside housing.
11. Remove the plate and starboard steering cable from the vice and replace with steering box with port side steering cable attached as shown in photo “H”. Using the vice-grips, begin turning the rod clock-wise until the cable stops – this will fully extend the tiller end of the cable.
12. Re-assemble the steering box and plate by inserting the plate spindles back into their gears – being careful not to turn the spindle positions. If necessary, turn the plate slightly to align the screw holes as shown in photo “I”. Once the plate is in position, replace the (4) four screws that hold the plate in place.
13. Reinstall the cable retaining bolts and apply waterproof grease to the both the left and right tube retainer fittings as shown in photo “J”. Greasing the retainer fittings should be part of the normal maintenance schedule.
14. Check the travel of the tiller-end of the both cables to make sure they both extend to the same length as shown in photo “K” – in this case, each end is extended to 9 ¼”
1 5. Use the vice-grips, turn the steering rod on the cable box all the way in the opposite direction to check the measurement on the port-side steering cable. It should measure the same as the starboard side with fully extended – in this case 9 ¼”. 16. Remove old steering box. 17. Secure the cables nuts by taping them into place so that you do not lose them while threading the cable through to the rudder step as shown in photo “L”.
18. When installing the new steering cables, first install the shorter cable (fully retracted), in this case the starboard cable. A fully extended cable will not fit in the rudder step until it is in place. The 19’ cable goes to the port side, the 14’ cable goes to the starboard side. There is a channel underneath the cabin doorway through which to feed the port cable. Photo “M” shows feeding the port cable through the back of the port aft cabin through to the rudder step. The cover panel has been removed for access. The cable is then passed through the aft locker and into the rudder step. Older model Gemini’s may require drilling or cutting out access holes for feeding the new Uflex cables.
19. Reconnect the steering cable to the rudder assembly in the rudder step as shown in photo “N” – showing starboard rudder.
20. Before connecting the starboard cable, be sure to turn the wheel completely to the opposite direction to retract the cable extension. That should complete the removal and install of your Gemini Catamaran mechanical steering system. If you have any questions please contact us
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IMAGES
COMMENTS
Welcome to Gemini Marine Products Our stainless does what others just can’t Our 316 stainless steel fittings, including our exclusive, patented hinges and struts, set new standards in marine canvas hardware.
The commany that now produces Gemini Catamarans. The original company, Performance Cruising, Inc. was unable to weather the downturn in the boating marked that started with the mortgage crisis in 2008.
Gemini Replacement Centerboard. Chesapeake Light Craft produces replacement centerboards for the Gemini 105M and 105MC multihulls at our shop in Annapolis. The 105MC started production in 2000, and like the originals, the boards are asymmetrical foils, available in... Telstar Replacement Centerboard
Go to: Gemini Marine Canvas; Shop our products Menu Toggle *New* grab rail kits; Strapless bimini conversion kits; Split and sliding side mounts stainless steel; Concave fork and post mounts; Hinges and GemLock folding struts; DrillSteady drill guide; Supporting hardware; Product specifications; See us in action Menu Toggle. Strapless bimini ...
Gemini 105M & 105MC. Power. Most Geminis 105M and 105MCs were originally powered with Westerbeke Diesel W30B3 3 cylinder engine (27 hp) connected to a Sillette Sonic Drive with a 16” 3 blade prop. The drive leg is no longer in production but some replacement parts are still available.
Gemini® Sr. Replacement Parts Detail 302015 301056 301060 131020, 131020B 131030, 131030B 301000 ... Gemini Jr. 80014 302090. 80039 80675. 301060. B9228. Rev 11/11 ...
Performance Cruising Replacement Steering Systems For Gemini Catamarans 105MC 3400 And 105M Series Boats Replacement Steering Systems For Gemini Catamarans [email protected]
These are the instructions that were produced and distributed by Performance Cruising on how to replace mechanical boat steering on a Gemini Catamaran. These instructions are a step by step process on how it is performed. Also included you will find what parts you need based on your model and hull ID and basic tools needed.
Gemini catamarans have been outstandingly popular in Performance Cruising's home US market with more than 800 boats built between the introduction of the first version in 1983 and 2004. The design and manufacturing process of Geminis is refined to boost the key virtues giving them continuing broad appeal to those who want to go cruising - good ...
May 6, 2023 · Re: gemini 105mc Rig Parts If the halyards are seviceable, I would love them. Also looking the a mast base which I am sure you reused but the casting at the end of the folded mast would be a good form to cast a new base if you can get it off.