Big Props on Airboats

speedchaser · Sep 23, 2004, 03:59 PM

I've sometimes thought of Airboats as there's less construction and they're very flat which I like, but the size of the props I've seen in pics puts me off - the diameter's so large - they look so out of scale/synch to the boat itself; I've been thinking that if you ducted the prop you might gain some cosmetic value - but probably not much... I guess the size of the props on Airboats is because there's less resistance in air than in water - and so the prop has to be big to draw in enough air (is that right...)? But if you turned the motor/prop around so that is pushed against the air rather than pulled on it (just as a water prop pushes agains the water), could you get away with a smaller diameter prop - just a thought... Any clues...?

CG Bob · 10:59 PM

Full size airboats tend to have large props. Air is not as dense as water, and need a larger diameter screw. Husky Airboats specs show a 6 foot diameter 6 blade prop on a 19 foot airboat. In the Wisconsin Apostle Islands area of Lake Superior, they use wind sleds to get out to the islands in winter. Wind sleds are reinforced for use over the ice, and look like airboats with a cabin.

Quote:

...and so the prop has to be big to draw in enough air (is that right...)? But if you turned the motor/prop around so that is pushed against the air rather than pulled on it

It doesn't matter too much if the prop is in front of or behind the motor. The prop still has to cut into the air on one side to push the air out the other. Think of a nut threaded onto a bolt, it takes the same amount of energy to turn the nut in either direction. The nut is similar to the prop on an airboat.

speedchaser · Sep 24, 2004, 03:41 AM

Right - many thanks for that... Full-size examples of marine craft that gave me the notion of smaller diameter props for model rc airboats or similar, are for instance hovercraft, whose props (although large) are relatively much smaller in relation to the hull than those for an rc model airboat. I know that hovercraft have irtually no water resistance for obious reasons, but then nor would airboats especially if they had strakes - so I just thought it might be possible to have smaller props - but your info of a real (?) 19 foot airboat having a 6-foot 6 bladed prop, probably negates that.

Sep 23, 2004, 03:59 PM	#1
speedchaser speedchaser Brighton, Great Britain (UK) Joined Sep 2004 167 Posts	Big Props on Airboats I've sometimes thought of Airboats as there's less construction and they're very flat which I like, but the size of the props I've seen in pics puts me off - the diameter's so large - they look so out of scale/synch to the boat itself; I've been thinking that if you ducted the prop you might gain some cosmetic value - but probably not much... I guess the size of the props on Airboats is because there's less resistance in air than in water - and so the prop has to be big to draw in enough air (is that right...)? But if you turned the motor/prop around so that is pushed against the air rather than pulled on it (just as a water prop pushes agains the water), could you get away with a smaller diameter prop - just a thought... Any clues...?

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Sep 24, 2004, 03:41 AM	#3
speedchaser speedchaser Brighton, Great Britain (UK) Joined Sep 2004 167 Posts	Right - many thanks for that... Full-size examples of marine craft that gave me the notion of smaller diameter props for model rc airboats or similar, are for instance hovercraft, whose props (although large) are relatively much smaller in relation to the hull than those for an rc model airboat. I know that hovercraft have irtually no water resistance for obious reasons, but then nor would airboats especially if they had strakes - so I just thought it might be possible to have smaller props - but your info of a real (?) 19 foot airboat having a 6-foot 6 bladed prop, probably negates that.