Pusher Propeller for Air Boats

What are the engine output rpms at full power?

3,400 - 3,500 at full power.

Most airplane props want to turn at 2000 to 2500 RPM.

These people manufacture props in all configurations, they may be helpful. I know of many people with air boats, all say these props are the top of the line. We have two boats in use with these props. One with Fire Rescue, One with Law Enforcement.

http://www.airboatprops.com/

bob do you have a personal air boat, i am building a wind turbine but cant find any place to test it it is 13 feet tall and the tallest wind tunnel is 8 feet in south florida , i am in miami atamiami airport

No. No unsupervised time with sharp objects for me. I have done some maint. work on the red boat, and some earlier work on the weed control boat. You might try contacting the So. Fla. Air-boat Assn. they would probably run up their boat in return for some gas money. Let me know if, and when you test it.

You could try here: http://www.arrowprop.com/low.htm

or here: http://www.whirlwindpropellers.com/html/airboat/airboat_miniprop.shtml

Is probably more than you need but they may have info on who makes what you need.

You may have luck searching for ultralight aircraft props or even industrial fan blades.

I have seen some high speed air boat props made out of aluminum and composites but this is also probably overkill for your little 16hp mobile floor fan.

Have FUN!
TT3

Turning a prop at 3400 rpm will make a lot of noise. Consider a belt drive setup that will slow the prop down to it's designed speed* while allowing the engine to operate at it's power band. This will also allow the engine to be set lower in the boat, for better maneuverability.

* If the prop spins too fast, the outer tip will go supersonic. At that point that portion of the prop stops moving air.

When that prop goes supersonic, it will get REALY NOISY as in muffs and ear plugs noisy.

Thanks to all for the quick responses and great information. My first step will be to build a hull. Any tips or advice would be welcomed.

thanks again!

Thanks TooMuchFun, great information! It sounds like you have done this more than once. Do you have any step by step photos of the process? I can give you my home e-mail address if you want.

Thanks again, Catman

Hello Catman [HappyCat]

Most of us just communicate by sending direct comment through CR 4, if you haven't tried that yet, it is simple to do, simply high light

TooMuchFun and hit the send message key and the screen will let you type in your message and it will be forwarded to me through CR 4.

AS for the plans, They exist only in my head until I get ready to settle in to seriously committing to a project. Then the first step is plans, as complete as is possible, including details, details, details, then comes the list of materials, so that I can start scrounging as much as is available. In this case, you must first consider designing the overall picture, then break it down into its components. The hull becomes much easier to assemble when you have determined all that it must accommodate. The interior framing to hold the embedded backing, etc, when all connected together will add strength to the hull. By drawing a scaled picture first, and then compare it to the "as-bilts', such as the size of the engine, the cage that covers the power assembly, the size of the rudders, etc., will help you to do some layout on a flat surface. In fact I would actually do a complete layout on my garage floor before beginning construction. You may be surprised at the changes that you might consider. Take it from someone who has done many such projects, " it is cheap to erase, it can be impossible to change after the construction is well under way"

TooMuchFun

I would suggest a ducted fan instead of a conventional propeller. These can be more efficient than a conventional propeller. The smaller diameter will allow you to mount the engine lower, which on a boat that small will be critical. I would also suggest a larger platform than 8' by 4'. If you based that on a standard sheet of plywood, it comes in larger sizes up to 16' long. 5' x 10' marine grade plywood should be available, if hard to find and/or expensive.

Years ago I had Popular Mechanics plans for a hovercraft, which had detailed instructions on building a ducted fan. They may still be available.

This sounds like fun! Now I want to make one! Oooh, how about a turbine instead of the Briggs?

A ducted fan is clearly another good idea, but requires a bit more skill than the average back yard builder can muster. However, I see no reason that such a power system could not be adapted to retrofit in the same area available. The important thing for "HappyCat" to consider is that his original framing embeds provide for such modified anchoring. Common sense would indicate to me, that though I don't want my engine below deck, I also don't want it 5' above deck. That requires additional metal work that can be avoided. The propeller should be belt driven, and the shaft can be located where best suited.

In fact, "If HappyCat is so motovated," he could even construct the prop shaft assembly very easily to accept more efficient performing, counter rotating propellers. This Idea provides for the added benefit of only having to deal with force of engine rotation when turning. Propeller shaft forces can be tricky to turn against, and very sudden responses can occur when turning with the other forces. All that is required to accomplish this is to place one propeller shaft, inside the other, and use drive belts designed to be twisted 180 Degrees. Even Ducted Fans can be constructed to accommodate this idea.

I have already given a great deal of thought to this subject as it and the hover craft have from time to time come up as an interesting project that I might enjoy. I have two 16 hp Briggs engines on the shelf looking for a place to play. Enjoy!

TooMuchFun

The ducted fan for the PM hovercraft wasn't that complex. There was even a source at the time for unfinished propeller blanks- you got the hub and basically square wood blades (at the proper angle) so you could customize the diamater and shape of the prop. Some fairly time-consuming woodworking, but. . .

Umm- actually, now that I think about it, not everybody had a grandfather who was a master machinist, patternmaker and coremaker.

Anyway I found those hovercraft plans online that included the ducted fan (just switch from a vertical to horizontal shaft engine): http://www.rqriley.com/plans.html

The one I have plans for is the Pegasus. The Tri-Flyer high performance hovercraft, minus the hover parts, would make the kind of airboat you want.

Hi Catman:

You are saying air cusion boat or just use pusher to push the boat go forward?

Suggest you go to http://oemsoftware.ec/index.php?target=desc&progid=4824

get a blade modeller first!

Turbine blade design start from basic aerodynamics and FEM analysis...etc.

If your use your 16hp engine to push the boat will definitely need to design boat shape reduce darg in the water first. Then talk about design the push propeller, and there are many propeller makers on line. You can check each one request the performanece data the decide which one is better.

My suggestion only, wish you good luck!