outboad hydroplane and motor choice?

[Yellowjacket]

Originally Posted by stupidbaker57

I am building a Hal Kelly hydro. It's a 11.3 3 point hydro. I plan on putting a 400cc motorcycle engine in it and driving the prop via surface drive. I have designed on cocktail napkin to scaled drawing to a wooden scaled version on the back of the boat. I have all the materials ordered and a few more to be custom made by myself. I have pictures of the wooden scaled version and soon will be building the final drive for steel and aluminum.
With this 27 HP engine I should aceive a speed of 48 MPH. If all works out, I'll be building another boat and mounting a honda 600cc water cooled that puts out 13,500 RPM's at peak.
Am I crazy? Maybe, but I've built some 'crazy' stuff in my life and I've made it to 63 years old.

You need to look at the weight distribution since your inboard with a surface drive will put more weight forward than the original outboard did. IF you can get a similar weight distribution by moving the driver further aft than it was in the original boat it could work. If not you could end up with an evil handling thing that will try its darndest to throw you out of it. Remember that the original outboard had a skeg and sometimes a turn fin at the back for stability. Make sure you have at the very least as much surface back there to keep the pointy end aimed in the right direction.

It does seem like a lot of work when you can simply buy an outboard with as much or more power for almost nothing. I bought a 1977 50 hp Merc a couple of months ago for $300 and it runs just fine.

You are also going to need the right prop and that won't be cheap either, but if you want to tinker go for it.