Snowmobile engine boat

[Minnesotaman]

Hi everyone, I'm thinking about building my first boat this summer but I have zero experience in building them. I would like to build a 10-11 foot little race boat for as cheap as possible but I have some questions concerning which drive system to use... This may sound dumb but I'm planning on using a 440cc snowmobile engine with out the clutches (only because I already have it and it would be a fun challenge). I'm hoping to use a direct drive (for simplicity) with a surface drive set up. Any advice about how to make a surface drive work on a little boat like this, what prop to use, or any other information would be much appreciated.
Thanks

O ya and I'm not worried about being able to run the engine in warm temps so don't bother telling me that it can't work.

[Submarine Tom]

Go for it. Have fun and don't hurt yourself!

-Tom

[dinoa]

Many of the watercraft engines in use today are multipurpose and with some modifications are used in off road vehicles, snowmobiles and even aircraft. Try Weber, Rotax and Yamaha for instance.

If you want to keep it really simple try a Thai longtail conversion. The kind they use in canal drag boat races.

Dino

[gonzo]

What is your experience on fast boats? A setup like that is likely to kill you. Look at videos online of racing accidents. That happens to professionals.

[TeddyDiver]

Why make a boat

[CaptBill]

Originally Posted by TeddyDiver

Why make a boat

Good point TeddyDriver, just get out there and don't make no saw dust.

HAHAHA

[CaptBill]

Originally Posted by CaptBill

Good point TeddyDriver, just get out there and don't make no saw dust.

HAHAHA

And don't let up on the throttle!

HAHAHA

[CaptBill]

Actually including the clutch will give you a neutral gear without any extra work, wouldn't it?

Also, all joking aside, you might be able to save a lot of time and energy by simply constructing a simple outrigger/pontoon arrangement that attaches directly to the FRAME of a snowmobile. You could probably even use a wrecked out frame you can get for free. Then you just need to do is get the balance and the clearance of the treads right. Everything else is done for you.

[gonzo]

A frame would make a heavy boat and defeat the purpose.

[Minnesotaman]

Thanks for the advice everyone. I really like the long tail idea and I think I might do that if I can't get a surface drive to work. Does anyone out there know if I would get prop walk with a surface drive set up? Also do I have to watch out for any kind of cavitation issues with surface drive? If so what should I watch out for?

[Minnesotaman]

O ya and the reason I'm not using clutches is because I don't have the clutches for the engine.

[gonzo]

You are trying to oversimplify. Boat design and behavior is part of a fairly complicated system, particularly at high speed. The type of drive alone is not sufficient to get an answer. Other things, like CG, bottom loading, deadrise angle, propeller design, etc. affect the end result.

[Minnesotaman]

I'm just looking to build something to drive around at my cabin this summer. It doesn't have to be pretty I just want something that will work and something that will be simple to build. I found boat plans online and I'm just trying to figure out how to modify it to make the snowmobile engine work. Gonzo how would you recommend I go about doing this?
Thanks

[CaptBill]

Those frames are built for those engines and they are generally very light. A lot lighter than what you will build yourself I bet. Plus you can remove what is not surrounding the motor itself. Retain the factory mounting is what I mean. Save a lot of headaches/work.