planing hull / air prop

[david carey]

is it feasible to use hovercraft type powertrain on a planing hull . Would there be problems with heeling/turning . The areas I am thinking of using the boat are lagoons where sometimes the depth is only 1-2 ft . I know this because my sailing canoe has a 2 ft centreboard .undefined

[jehardiman]

Yes, they are called airboats and have been in use in the southern USA for about 80 years.

http://www.airboattrader.com/

[FAST FRED]

The big hassle is THRUST .

An air prop will convert 1 hp into about 5 lbs of push (7 with theoretically Perfect prop)

A water prop will easily produce 20 lbs of push for each HP , with 25 or 27 not unheard of.

So are you willing to have and feed an engine 4 or 5 times larger than a wet prop would need?

FAST FRED

[John Perry]

Originally Posted by FAST FRED

The big hassle is THRUST .

An air prop will convert 1 hp into about 5 lbs of push (7 with theoretically Perfect prop)

A water prop will easily produce 20 lbs of push for each HP , with 25 or 27 not unheard of.

So are you willing to have and feed an engine 4 or 5 times larger than a wet prop would need?

FAST FRED

Depends on the diameter. A water prop provides a lot more thrust for a given power than the same sized air prop but if the air prop is large enough it could be as good, perhaps even better because it is not affected by cavitation/ventilation. The 'de-cavitator' project, fastest ever human powered boat used a large air prop because they reckoned it would be more efficient overall, interesting one of the main factors here was the elimination of water drag on the prop shaft, presumably the air drag for the air prop support tower was less than that for the water prop propeller shaft. The practical points are that for a given thrust and reasonable efficiency the water prop will be much smaller, hence cheaper and lighter and less generally intrusive, less noisy and probably safer for passengers if not for swimmers. Air prop maybe worth considering for very shallow draft, very high speed, or special requirements like the 'de-cavitator' boat. Or for flying boats of course.
John

[david carey]

thanks for the replies . I am aware of airboats but what i was picturing in my head was a conventional deep/medium vee speedboat hull with a inboard engine mounted low in the hull driving one or two airprops , therefore having nothing to damage below the waterline and capable of going from lagoon to river and then to sea .

[Corpus Skipper]

If you're not going into much less than 1 foot of water, check out www.smithboats.com/whoweare.htm. Inboard + shallow draft = powervent