G'day, Resolving the quandary. Matt's boat runs at 4 knots on 18 watts. Its also possible that his calculations included just the power to move the boat, not the power to raise the paddle in which case the total power to propel the boat might be 18W plus 8W to raise the paddle ie. 26 Watts. Its also possible that some of the power used in raising the paddle blade is returned and contributes to moving the boat by: positioning the blade, as a counterweight to the opposing blade and as a propulsion force as the blade falls through the water. Lets say a net value of 50% power returned. If that's the case then the net power to raise the paddle after subtracting returned useful power becomes 4W, and the total power becomes 26W minus 4W returned power so we have a ratio of 4W net average power to raise the blade and 22W total average paddling energy. Thats using my paddling stroke. With Niels stroke it would be 8W net to raise the blade and 26W total for paddling. This actually sounds reasonable if my assumprions are anywhere near correct and I'll now take my hat off to both Niels and Matt. For what its worth: Niels I'm happy with your ideas - seems to me they give credible answers; and Matt I should never have doubted but I'm happy with your values for kayak power. Many thanks for all the information and discussion. All the best, PeterO *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
rebyl_kayak_at_energysustained.com wrote: > > Matt's boat runs at 4 knots on 18 watts. Its also possible that his > calculations included just the power to move the boat, not the power to > raise the paddle in which case the total power to propel the boat might > be 18W plus 8W to raise the paddle ie. 26 Watts. I think Matt performed his measurements in a tank with flowing water, measuring the force on a rope that kept the kayak in place. There are no losses in such a test. When paddling, there are losses (it seems Matt and I agreed to estimate them at 50%) so you'd need twice that 18W to paddle a boat at a speed of 4 knots: 36 watts. That's the energy you have to transfer to the blade; it doesn't incorporate the losses within the human body. Those will be considerable. > Its also possible that some of the power used in raising the paddle > blade is returned and contributes to moving the boat by: positioning the > blade, as a counterweight to the opposing blade and as a propulsion > force as the blade falls through the water. Lets say a net value of 50% > power returned. I maintain that 100% of the power is returned to driving the paddle through the water. The 50% loss is AFTER that. > If that's the case then the net power to raise the paddle after > subtracting returned useful power becomes 4W, and the total power > becomes 26W minus 4W returned power so we have a ratio of 4W net average > power to raise the blade and 22W total average paddling energy. Thats > using my paddling stroke. With Niels stroke it would be 8W net to raise > the blade and 26W total for paddling. You KEEP dividing those 30 watts by two. I maintain that you're wrong in all those cases: The vertical rest can add 30 watts to whatever other power you're putting in. Of all those powers, only half is coming out: 15 watts from the vertical rest, 50 watts from the 100 watts you might put in total. I made new measurements, that confirm those 30 watts as the output of the blade - check the video at http://www.youtube.com/watch?v=io6S_gRxk8c . It will take another 5 minutes of your time, but it might clear up a lot. Niels *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:33:55 PDT