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fastest raft Answered

Hi ppl, im making a raft for a charity raft race and was wondering if anyone had some design ideas. I want it to be the fastest thing in the water and want to know how this can easily be achieve using fairly readily available materials? The raft will have to hold 2 people, and will probably be powered by pedalling. Any ideas?



Don't pedal to power an underwater propeller - the size and angle of the blades must be closely matched to the engine power and boat size.

Make a pedal-powered fan boat.

. Do you think two ppl could produce enough thrust with a fan? Most airboats I've seen have motors putting out 10's (and sometimes 100's) of HP. But then, I have no idea how many HP two ppl can produce. . Intuition tells me a direct-drive paddle-wheel arrangement would be more efficient and much easier to build.

probably at most and average of 1/4 of a hoursepower person so this is a good point, i believe a paddle wheel would be the best idea, although am not sure if this would be faster/slower than a propella in the water.

OK, how about a human-powered jet boat? Gear the bikes to the input shaft of a centrifugal pump just under the water? If you were willing to sacrifice thrust for show, part of the jet could be re-directed to give the classic jet-boat rooster-tail. I would suspect that the impeller of a leaf-blower could be persuaded to serve as a water-jet for a few hours at least.

. From my POV, fans, props, and jets are not feasible for human-powered craft. They all run at 1000+RPM, which is going to be difficult to achieve (and maintain) with a DIY project. A paddle-wheel will work well at 10RPM.

. Wow! That's cool. But remember, the "rolling resistance" of a boat is much higher than a trike and a lot more thrust is required, which means bigger/faster fans. I'm not saying it won't work, just that, IMNSHO, it would be a lot more trouble than it's worth for a one-race, DIY project.

linky doesn't work ?!? how about a paddle wheel?

Those flat-bottomed swamp boats with a dirty great aircraft propeller on the back.

. Hmmm. It doesn't work for me unless I get rid of "_w".

. LOL If I had been thinking at the time, I would have included the correct link. Thanks.

We all have our lapses (or whatever you call them LOL).

ok, I thought you might go for something more elegant (little did I know LOL) I have momentary excursions, myself LOL

thanks links working now! i dunno though do you really think it would be very fast?

did anyone see the episode of viva la bam when he and his friends made rafts

. In general, the more rigid the hull the better - flexing is wasted energy. . Keep the leading and trailing edges tapered for improved hydrodynamics. Slice through the water, don't just bulldog your way through. . Use the lightest materials possible without sacrificing rigidity (eg, Al). . Keep the center-of-gravity low (eg, mount your seats low) to keep wobbling to a minimum - wobbling is wasted energy.