Ok I will admit I have seen quite a few things that puzzle me. I notice that some boats have a tube that looks to feed air to the prop on some boats. Is this to increase cavitation or efficiency? I know that if you unload the force on the unloaded prop egged one can see a return in efficiency. Here is the question...... what are the applications, is it something any boats that DONT cost 1 million can benefit from? Finally I would not think a surface drive would benefit but correct me if I am wrong. Please post some info if you have some.

That is so boats with big power turning big pitch props can caviate the props when coming on plane. The props get a little air and it allows them spin more freely and allows the engine to build rpm more easily. It is so the boat will plane easier and doesn't really affect anything else.

I only recall seeing the tube on #6 drives.

I havent seen very many either. Motley crew and an old Mrs gieco. All of what I have seen are not surface drives. I can see a reason for motors that dont have low end but most shouldnt have to worry. Thinking that resistence is lowered by allowing air to "relieve" the water from the low pressure or unloaded side of the blade, like a surface drive. What I dont get is my boat can blow the props loose at take off all the way to when it gets to plane and I only have 500hp per side, and they are deep on take-off 3 feet.