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Cut and Fold Aluminum
"Bruce In Bangkok" wrote in message
... On Sat, 12 Dec 2009 14:01:13 -0700, "Bob La Londe" wrote: This has been bouncing around in my head as well since you forced me to think a little more. The reason I think a sharp edge is more efficient is basically the same as why a pad is more efficient at optimum speeds. The sharper edge will break the surface tension and shed water weight and reduce resistance much sooner than a rounded edge. The average boater will never notice the difference, but guys who are always running on the ragged edge (oxymoron not intended) and looking for the best performing prop to run right at redline will notice the extra 1 or 2 miles per hour. Rather then "surface tension" I suspect (if the effect is not large) that it is simply a matter of surface area. Exactly the same reason that the small flat bottom is faster then a vee. At any speed it would take more "lift" to raise an inclined (vee) surface then one at right angles to the force, thus any rounded corner would act much the same as the vee, for that portion of the pad, and reduce total lifting force, by some percentage. That is certainly part of the equation now that I think about it. Surface tension has an affect as well. I'm sure the answer is not one dimensional. However.... I have read that the multiple, sharp edged, chine designs actually increase speed because the sharp edged chines increase the amount of air that is trapped and forced to flow under the boat but whether that works to decrease drag by reducing the viscosity of the water or by reducing the wetted area I don't know. That could be both. Air cushion is definitely a factor in many designs but I am not sure that it's the primary factor in multiple chines. Seems I read somewhere that multiple chines was to increase lift at various speeds until the boat is at optimum cruising speed. Basically the multiple chines help it come out of the hole faster. I seem to recall and I think you mentioned it in passing earlier in this thread that it also helps with stability and steering control. If you have ever run a flat bottom boat that is adequately powered I'm sure you know that it planes out almost immediately. The way it was explained to me is that multiple chines are a compromise. Gives you more lift like a flat bottom, but as they come out of the water they cease to create drag. Now I'm tempted to start a whole new thread on air cushion designs. Tunnels. Twin tunnels. The big M shape of the front 1/3 to 1/2 of many of those modified V-Pad bottom boats. We could talk about lift, cavitation, kiting, Miss Budweiser doing end over end flips, LOL. My experience with tunnels is more limited, but I did have a Baker Custom Boats twin tunnel for a few years. Awesome ride in light chop. I think we can both agree that the less boat you have in the water (in general) the faster it will go. ** Thought I better throw this in: ** Chine walk can be deadly scary in such a boat if not properly setup or if driven by somebody who hasn't taken the time to learn to drive their rig. The biggest safety move for anybody else reading this is to SLOW DOWN gradually. A sudden loss of throttle can be almost as dangerous. Especially in traffic in a busy system. Increase power (like I did) and it's a whole new rig to learn to drive. Left that last bit in because it bears repeating. Bob La Londe www.YumaBassMan.com |
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