Maximum efficiency prop for a WIG boat

Originally Posted by baeckmo

Starman, the question about propulsion efficiency cannot be properly adressed until we have something like a basic idea of the resistance of the craft as a function of speed. As I mentioned before, overcoming take-off resistance is a balance between drag reduction and thrust. The thrust characteristics of ventilated propellers (which is what we would have in your case) has a dip in the speed region, where the WIG actually needs high thrust. If my memory serves me correctly, there are some WIG's propelled by outboards, and in those cases, the propeller is actually controlling/limiting the flying altitude.

All fully submerged propellers (air or water) obey the same physical laws. High thrust at low speeds come with low efficiency and vice versa. Again, without knowledge of the craft's drag it is not possible to say anything like "Air propeller has x % efficiency"; it depends primarily on speed, thrust and propeller diameter. So: a preliminary drag curve is essential in order to have a starting point for the design spiral.

I understand that, thanks, but it no longer matters since I've decided to use an air prop. From what I've read here the surfacing props have 70% efficiency at best and the air props are a little better. Also the water prop will be subject to be more easily damaged and that is a fairly big negative point.

Sometimes it functions in the end...............

Originally Posted by daiquiri

"it's closer proximity to the water and wider chord prevent it from nosediving and digging in" - Maybe it is just a typo

Not a typo, a misunderstanding. 'It's closer proximity' meant "when it gets closer" when it gets closer it creates more lift. So elemental and yet you correct me by agreeing with me

But you ignored the important point about stability, which is what I was talking about (I said "this is for stability"), and that is the CP travel with proximity to the surface and the instability that causes. I'm sure you know all about that so we will drop it now.