re powering a 16 foot hydroplane

Does anyone know why I can't put an inline 4 cyl motorcycle engine complete with with 5 speed transmission, hooking the drive shaft to the prop of a 16 foot hydroplane??? I was thinking of a fuel injected water cooled job with a cooling fan in the nose of the boat. I am a certified auto mechanic, but the water has different needs. Will I run into problems??? Suggestions, and experiences to share???
Roger

 

you won't need the transmission. You may need a reduction gear though to reduce the rpms.

 

The transmission can be used, but you'll only use only one gear. In fact, a common back yard trans was the old truck 3 speed (343 Saginaw) bolted to a small block Chevy. The trans was disassembled and everything removed except reverse and first. The gear you use will depend on how fast you spin the engine and props for the speed range you desire. The small blocks liked 2.5:1 which worked out just fine with these old trannies.

Motorcycle engines aren't designed for this type of "duty cycle" so it'll have a poorly matched cam and will not live long, if asked to act like a boat motor, but you can have some fun for a while. This coupled with the need for spark arrested electrics and intake, or a completely open engine bay, may make you reconsider the idea.