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post #8 of Old 07-01-2012
jerryrlitton
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Re: Beneteau 36CC does not reach hull speed

Your GPS shows 5.1 Kts. You have a .5 KT wind on the nose. Hull speed is supposed to be 7.48KT.
1st you are mixing apples and oranges. Your GPS will show you speed at a given time over the earth. It is showing you the sum of the efeect of boat performance, wind/wave action and current. It will not show you the isolated hull speed. It is no way a performance instrument. If you want a performance answer you need to measure speed through the water. For this a current on the nose or stern makes no difference. However the wind will. What you do need is something that will measure your speed through the water and have no wind, That will get you very close. If you must rely on GPS then do it without wind and current. The other cheap and accurate way is to throw something that floats in the water with a very low free board at the bow and measure with a stop watch the time it takes to reach the stern. Now you have a simple time/speed/distance formula to work with. Just like they did several hundred years ago. But it works.

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Last edited by jerryrlitton; 07-01-2012 at 02:08 AM.
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