h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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Take a kayak/canoe hull and install a water intake in the front with the line running to the intake port of a centrifugal pump whose shaft is turned by a pedal powered link chain. The outflow of the pump is routed back and out through the transom. Advantages: same draft as original hull, mechanism
protectected from grounding and rocks, uses leg power very efficiently since no energy wasted turning power through a right angle as with a prop. No chance of "skating" as with an open paddle wheel. Could be used either with a hand operated steering mechanism or with a standard double bladed paddle, perhaps with both. Down here in Texas we have races down river to the Gulf every Spring. These involve so much portage, lugging over obstacles etc. that they are almost amphibious marathons and are usually won by teams in very light fibreglass boats. I think a device like this would give a solo boater a chance in the "unlimited" class.
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Maybe a gear pump instead, in that case - no turning of the jet or of the driveline. I'd like to see one of these. [+] |
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Not sure whether it would be better than a kayak powered by paddles or not; I suspect not as a paddle pushes a large volume of water relatively slowly (low turbulence and hence low vortex losses) whereas a pump of suitably small size is going to have to accelerate the flow much more as it passes through the pump; there are inevitable losses here. Doesn't mean I wouldn't like to try one though. |
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You are going to get power losses in your link chain, in the water lines and in the pump. You are also going to be weighing down your boat with all the water in the lines and in the pump housing--if you make the water lines bigger to reduce flow losses, you further increase the volume/weight, and must increase the size of the hull. |
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Plus, you are going to have to drain and fill all that water at every portage, or lug it with you. A centrifugal pump designed for water isn't going to prime itself very well. |
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There are a lot of centrifugal "jet-drive" boats around here, using a unit that replaces the lower unit of an outboard motor. They just aren't as efficent as propellors. |
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I class this idea as one of those that occurs often, but isn't going to work, which is why you don't see it done. |
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