At 11:44 PM -0700 5/28/99, Matt Broze wrote: <snip> >>When John says "Boats create their bow wave.", it sounds a little obvious. >>We didn't think evil demons were doing making them. But, what it means is >>that the boat can not avoid the wave. If there is a lot of drag the wave >>will be big. If the boat can power its way through the drag and get into >>another drag regime, the wave will change. If the drag diminishes, the wave >>will diminish. You can't climb over the wave because the wave is basically >>innocent. The wave is a side effect, not a cause, of drag. >> >>This is not completely true because the changing wave shape can change the >>flow of water around the boat and this can change the drag, but it is not >>really the wave itself creating the drag. Drag is from friction and >>viscosity. > >Same question. When the waves cancel each other out (and disappear) the drag >is reduced as well. If the drag has already occured and the waves are only >the side affect of drag and not also a cause how do you explain the >reduction in drag when waves cancel each other? We get into a chick-and-egg thing here. The wave size reduces, so the drag reduces, so the wave reduces, so the... What started the cycle? Without drag, there would be no waves, but once there are waves, they don't make life any easier. It takes a lot of energy to make and sustain waves, so in-so-far as the waves need energy to be produced, they are "causing" drag. Waves involve a lot of rapidly moving water, and viscosity makes the water reluctant to move fast. If the hull motion through the water is such that it requires the water to rapidly move a lot for the hull to pass, there will be more drag than if it can pass without the water moving much. I suppose in this sense, you could say that it is the motion of the water moving in the waves which is the source of the drag, and by cancelling out the waves, you have reduced the drag. The other way of looking at it is that the hull that cancels out its waves is one where the water is displaced in the most efficient manner, with the least amount of water motion required (least drag) and thus it doesn't make any wave. While the fact there was a wave may have made the drag worse, the only reason there was a wave is because there was drag. By somehow reducing the drag, for example by making it so the water is not forced to move in a wave, you reduce the need to make that wave, which in turn will reduce the drag, thus reducing the wave... I don't think it matters if you design boat by reducing the wake size or by attacking drag directly. There is obviously a correlation between the size of the wake and amount of drag, so reducing one reduces the other. But, it is drag that is source of the wave. There will be drag without waves, but there will be no wave without drag. Viscose drag will be reduced by keeping the speed at which water is displaced around the boat at a minimum. The mass of the water displaced is also important, but it is more important to keep the water moving slowly. Nick Nick Schade Guillemot Kayaks 10 Ash Swamp Rd Glastonbury, CT 06033 (860) 659-8847 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Tue Jun 01 1999 - 09:23:19 PDT
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