Jere Lull wrote:
In article , Albert P. Belle Isle wrote: As a quick calculation, 24ft DWL would yield a hull speed of about 6.6kt with a speed-length coefficient of 1.34. To get to 7kt, the effective DWL at 1.34 would be a little over 27ft - not 35ft. We've sustained much higher speeds, but don't feel like opening myself up for someone saying that it's impossible, that I'm surfing, my knotmeter's off, there's a current, or some such. I would agree except that I eliminated all those things. We really have done "impossible" things. Would love to know how, but gave up and simply enjoy. It isn't a trick. The rule isn't a natural law, it's a general guage, and it is inaccurate in most cases. It might hold true for any one hull shape and weight, but it does not imply any limit, it is only an estimation of a constant of some sort we call hull speed. It's really all a question of fuel or propulsion force mileage. If you can ignore current and wind, the distance per gallon would be less at high speed than at low. There might be a "resonant" speed at which you could get the best mileage for your hull form and weight. You could plot a few speeds and fuel economies, and calculate a number which might express some value for, call it formatic drag, for want of a higher education... Each boat would have it's own value. A good comparison might also formulate the "answer" as an expression of fuel cost per mile / hour, or in effect how much it would cost per voyage in terms of dollers per hour wasted or saved in transit. In other words, to express the cost in fuel efficiency as a term that implied impatience, or something. Me, I like to spend as much time as possible on the boat, so don't count "slow" as a cost. A floating raft is almost as much fun, and you can fish! The more time wasted, the better fuel economy? How much per hour to save each hour wasted? How do you value your time? Terry K I use english measure for the sense of familiarity. Old rules of thumb last just as long as the thumb, I guess. |
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