In the discussion about speed and short boats some people may find the following interesting. 1. The waterline lengths of many of the shorter sea kayaks (Coaster, Speedee, etc.) are actually quite long relative to the overall length (i.e. short overhangs in the bow and stern) whereas many "long" sea kayaks have long overhangs. For example the 20' Looksha II has a waterline length of 16.16' so the overhangs are approximately 20% of it length. For comparison the Coaster is at 13.44' is 12.76' on the waterline and its overhangs are approximately 5% of its length. So, when comparing lengths it pays to look at the waterline length rather than the overall length. 2. If displacements are similar, the shorter boat will often have less wetted surface than the longer boat. For this reason the shorter boat will likely have similar resistance at lower speeds where wavemaking resistance is a smaller portion of the total. For example, at 4.0 knots the Coaster has 11% more resistance than the Looksha II (Results from KAPER) but at 3.0 knots the Coaster has only 2% more. (I chose the Looksha II only because it is a much longer boat than the Coaster. No other reason) 3. The studies I have read so far suggest that a just noticeable difference in exertion (a difference that can be noticed 50% of the time) tends to be +/- 10% so in the speed range between 3.0 and 4.0 knots the paddlers may not notice much difference between the Looksha II and Coaster. Once beyond 4.0 knots the difference climbs rapidly becomes more noticeable. I noticed the term "hull speed" rearing its ugly head again. Keep in mind that "hull speed' is not a limit to speed. It is the speed at which the length of the transverse wave produced by the boat is approximately equal to the effective waterline length of the boat. This quote from "Introduction to Naval Architecture" by Gilmer is a good one. "Hull speed is somewhat analogous to the 'sound barrier' for aircraft, which is not really a barrier but a practical limit for economic transportation" Gilmer was talking about ships an few ships have as low a displacement/length ratio as kayaks. For heavy short boats it does represent a practical limit to speed but for light, long boats like sea kayaks it is just another point on the graph. Even old, worn out, unskilled paddlers like me can paddle sea kayaks at speeds well above "hull speed". *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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