Re: [Paddlewise] A new way to teach the forward stroke?

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
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