My observations

[Papee]

Dave's Direct Drive Low horsepower mini airboat hypothesis.

In my past 20 years of experimenting with mini airboats and low horse power engines, I've come to a conclusion of what I believe to be the best direct drive setup. This setup is not written in stone, it is different to each engine and prop setup.

I believe that running an engine at 85% of it's capable rpm makes a reliable and efficient boat. Using the prop as a "rev limiter" to keep the rpm's down to this % works the best for me in these situations.
If you choose an adjustable prop, you can put pitch into the prop giving you the most thrust possible while holding your engine rpm down to this 85% number.

In this situation, you just can't pick a motor and throw it on any boat,you need to choose a hull size that fits both the motor and prop combination. Ideas on hull sizes are many. My idea on this is that with a mini airboat, it is important to get the hull to float taking the least amount of water possible. Common sense tells us that if a hull is already floating in less water, it will take less thrust to get it on plane.

On the other hand, if you make the area of hull contacting the water to large, you will cause to much drag for your low horse power setup to move fast enough to get on plane. So there is that "sweet spot" where you are balancing the buoyancy of the boat and the drag cause by the hull surface area. Carefully planning out all of these factors will give you the best result in your Direct Drive mini airboat in my opinion.

[bubbasmacks]

Hey sorry I have not been on here in a while, I am in sector right now and only get to the computer every once in awhile but, I do agree with your observations I love this sight Before it was trial and error or buy some plans that are hard to read and maybe it works. Hell, I love building boats and since this sight I have learned alot of stuff that I never knew by trial and error Keep it up and I will donate when I find time to get on these dinosaur aged computers and doit....BUBBA