I am considering a new outboard for my 44’ trimaran. Engine hangs over the port side on a retractable nacelle; and is presently a 2004 Honda 20HP, 20” shaft. Need a 25” shaft to keep the engine in the water. No 20 HP, 25” shafts are available, so want input on going down to a 15 HP Mercury, High Thrust prop. Boat weighs about 9,000 lbs.
New outboard for trimaran
- Thread starter Waltonsmith
- Start date
Looks like you can get a 5” shaft extension for a tohatsu 20hp and others.
http://www.baymfg.com/kits/tohatsu/
http://www.baymfg.com/kits/tohatsu/
Thanks for the input. I am now considering a 25HP Yamaha with 25” leg. The 15HP would be adequate but not great. New engine warranties are voided with modifications like the Bay Engineering extension to 25”. However, the Japanese engines are so good now, warranties are less important.
I would recommend you opt for electric tilt. The standard tilting mechanism on outboards is designed for short shaft and will be extremely unbalanced on a 25” long shaft engine, making it difficult to lift.
Larry, Thank for that input. I have to use electric tilt as the outboard “hangs” over the side on a nacelle. When the engine/nacelle combination is down, it is 3+ feet below the cockpit. I use a winch to hoist the unit up, and then electric tilt to keep the leg out of the water. The nacelle used on this boat was designed by a famous multi-hull designer/builder, Walter Greene In the 1970’s. Pulling the engine up is very much a”multihull thang”. Just another one of the oddities with trimarans. https://en.m.wikipedia.org/wiki/Walter_Greene_(multihull_designer)
Re. Electric lifts, in my experience, they sometimes don't lift as high and the bracket is larger, making for more drag in the water. This is the case with Yamahas, so just check the details.
The other thing I would think about is twin engines. My last boat (PDQ 32/34 catamaran, 9000 pounds) had twin high thrust 9.9s, and that was pretty strong. The maneuvering is great, the redundancy nice... but maintenance is 2x. I would not spread them too far (~12 feet) because beyond that single engine thrust is too unbalanced.
The other thing I would think about is twin engines. My last boat (PDQ 32/34 catamaran, 9000 pounds) had twin high thrust 9.9s, and that was pretty strong. The maneuvering is great, the redundancy nice... but maintenance is 2x. I would not spread them too far (~12 feet) because beyond that single engine thrust is too unbalanced.
Hey #waltonsmith, I looked up the Explorer 44 Trimaran and see some images from the Chris White site? Is that what you have? Looks like a “sweet ride”. Who built it?
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Larry; It was built by Lonestar Multihull in 2004. Quite a few modifications from the original Explorer 44 design, including the use of an outboard. Bay Manufacturing makes a 5" extension for a Yamaha 25, both the Portable model and the High Thrust model. No change to manufacturer's warranty. Right now I am trying to find out if the HT model has a carb or EFI. With ethanol gasoline (10% going to 15%?) , EFI is desirable; as I understand it. Multiple 9.9's or 15's would make for good control; but I have a set-up to rotate the engine in line with the tiller. Also, the engine is "canted" about 15" aiming at the dagger to make it run straight. Great boat so far. Owned it less than 2 years.