Harold wrote: >>>>>All the discussions seem to assume that the power output is all going to drive the boat forward at a constant speed. However, the boat/paddler mass is alternately being accelerated by the paddle stroke and then decelerating between strokes. It seems that, given a large enough engine, a large-bite paddle can be pulled through the water quickly. But if power is limited, a smaller paddle allows higher reps, which minimizes the period of glide between strokes and therefore the subsequent loss of energy due to acceleration/deceleration. The closer together the strokes come, the less deceleration there is between strokes and (I assume) the more efficient the biomechanics / stroke / paddle combination becomes. You occasionally see extreme examples of this where a powerful paddler pulls a massive stroke and then pauses for a long glide before taking another huge pull on the water. The inefficiency of this style is pretty obvious as his boat lurches forward and then settles back down into the water. On the other hand, you see Greg Barton churning away with very high cadences and very short strokes, leaving the big-bite Neanderthal days behind. Can the efficiency gained by this factor partially explain the discrepancy which is bothering Matt? Quantitatively, how much difference does this pulse-drive factor make?<<<<<< I wrote the following for a Sea Kayaker article back in 1992 (Note: Since I copied this directly from my computer it is probably what I turned into Sea Kayaker---so after editing it may not have all gotten published and I'm too hurried to check just now)? "Reducing the swing weight of the paddle allows a faster transition between strokes. This reduces the amount the kayak must be accelerated during each stroke to recover the speed lost to friction during the interval between strokes. It takes more energy to accelerate a kayak than it does to maintain its speed because now inertia (as well as the already present forces of friction and wavemaking) must also be overcome. The frictional and wavemaking resistances (drag) also are higher with greater variations in speed. The energy savings from the time spent traveling at less than the average speed does not balance the extra energy used travelling at more than average speed. This is partly because frictional resistance increases at nearly the square of the speed. Also, when travelling at or accelerating to the speed where wavemaking resistance becomes a significant factor (around 4 knots for a typical sea kayak) resistance increases at near the fourth power in relation to the speed increase. A more even speed is consistent with the higher paddling cadence that less blade weight allows." Back to the present. A higher stroke rate for whatever reason (such as with using a shorter paddle) would have the same speed smoothing benefits. I don't think this accounts for the apparent problem I'm having with the different paddles since it appears from the data given us that each stroke moved the kayak roughly an equal distance through the water and the higher stoke rate therefore made for a directly proportional (to the stroke rate) increase in speed (with its even larger proportional increase in drag). I think that is a far larger discrepancy than can be accounted for by the above. Partially, well I'd agree with that but, but only a small part. Here is another interesting tidbit from that same article draft that I just discovered: "[John Winters reported (in CanoeSport Journal V3,#4 Winter 1990, with blades pulled straight back at 90 degrees) that his experiments have revealed that for a given blade area the narrower (higher aspect ratio) blade will have less slippage. He theorized that the narrow blade's greater perimeter for a given area means a longer turbulence (drag) creating blade edge." John, this appears to be just the opposite of what you wrote in a recent e-mail on Paddlewise. I am curious what it was that gave you reason to have changed your thinking on this (if in fact I have interpreted both items separated by a dozen years correctly). Matt Broze http://www.marinerkayaks.com *************************************************************************** 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/ ***************************************************************************Received on Fri Jul 26 2002 - 01:26:58 PDT
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