Flexible drive seems to work well, at least for modest power . A chap called Rick Willoughby, in Australia, has pioneered the idea of using flexible drive shafts to very good effect on his human powered boats, and I saw a contender in that cordless tool race use a very similar set up to good effect. What's interesting is that such a drive system is self-stabilising, something that seems counter-intuitive at first.
The only problem with model aircraft props seems to be finding ones with a high enough pitch. The rough rule-of-thumb for efficiency suggests that the pitch should be about the same as the diameter, or perhaps somewhat greater. Often, the readily available model aircraft props are somewhat finer in pitch than this, probably because a lot of model aircraft motors normally run at high rpm.
Paramotor props are pretty big (I fly one, an H&E R120), usually around 40 to 50 inches in diameter. They are certainly cheap though, and it's possible that one of the Far Eastern suppliers of props might be persuaded to make a somewhat smaller.
Jeremy
--- In electricboats@yahoogroups.com, Michael Mccomb <mccomb.michael@...> wrote:
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> the model shops were going to be one of my next stops.... i have read that there are people who simply couple a generator shaft to a steel cable, the other end of the cable to a prop of some kind and then throw the prop end overboard to gen while sailing.... i guess you'd have to make certain that the thing stays submerged but the net result is the generation of current....   there are some pretty well designed propellers out there for paramotors (people paying close attention to foils in order to get the absolute maximum thrust) and I am wondering how one of these props would work out being drug behind a boat? you'd certainly be able to get a large diameter very easily.... as you point out the model aircraft people also take this all very seriously so I figure I'll pick of a couple small props and see what happens when i drag them through water. i'm certain that the larger props especially are too flexible but still it seems interesting and
> i am curious about the possibilities....
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