Dragonfly Airboats, Pemberton

[Paul Marshall]

Well, Ill try this again. I have been looking at the minis for awhile and just don't have the cash to buy one outright. Im trying to get a little more input on a way to build my own. Ive mentioned putting polymer strips between the ribs on my hull ( an 11-36 Lowe ) to create a smoother bottom, Im thinking a 34 hp Kohler engine,( not sure if I need reduction, Ive heard over 3600 rpm I would get stall an the prop ) and using a culver prop. Is there anyone other than a professional builder that has done one of these and can an average guy do this with the help of some knowledgeable folks ?

[Papee]

I'll try to make this as simple as I can. First, the info about the prop was somewhat correct, most props are made to turn no more than 3100 rpm so turning them faster would do no good and also be dangerous.

I have done a few boats using a Jon Boat hull but they are not the best to use. The big problem for me was I run an airboat because I run in low water and rocky areas. A Jon boat is not made well enough to endure these conditions, the problem I had was rubbing the bottom of the transom on the bottom or hitting it with a rock once in a while. I was always putting holes in it and repairing.

It takes a certain amount of thrust to move the floating weight of the boat. Most smaller motors just don't have the power to move this weight and a reduction drive has to be added to allow the motor to turn a bigger prop. A prop will only make so much thrust before you have to move to a larger prop or engine setup.

The next problem would be the width of a Jon Boat, they ae just a bit too narrow to make good lift to get the boat out of the water. The more water a boat takes when floating the harder it is to get it to plane. The better a boat floats taking less water the easier it is to get on plane. On the other hand, you have to have enough thrust to get the boat over the top. This is where the boat is almost on plane but still pushing water, if your boat does not have enough power to get past this point it will not run on top of the water.

More on the motor/prop. What you do is match the prop to the motor, using the prop as a "goveror" so to speak. You match the prop to the motor so it will not turn over 3100 rpm. This is the same when adding a reduction drive, you match the prop to the motor concidering the redrive.



I'll leave this sink in and if you have any specific questions I'd be glad to answer them.

[Paul Marshall]

Thanks Papee, I guess Ill resign this idea to whenever I win the lotto then. The price of aluminum is too great to buy for me, so building a new hull is out. I thought maybe plating the bottom with polymer would help with protection but if it is too narrow, that wont work either. Guess I had higher hopes than I should have

[Papee]

I wouldn't let this discourage you from building. That's how I started out, just don't expect the same performance that a airboat hull would have. I wouldn't do anything to the hull, just put a motor on it an see what it does. I built a 14 jon boat with a 25 hp motor on it for a friend not long ago and if he would have put a new prop on it I/m sure it would have planed. I put an old home made prop on it that I cut down and repitched. I'm going to do one at some point and use this 4a032 I have here. Soon as I can find a jon boat at a reasonable price.