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  #11  
Old 07-03-2007
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tim-

It is far more likely that the knotmeter is less accurate than the GPS.
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  #12  
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And CCA-rule boats sail above hull speed (albeit not as fast as surfing) by virtue of an increased waterline length when heeled.
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  #13  
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Quote:
Originally Posted by seabreeze_97
And CCA-rule boats sail above hull speed (albeit not as fast as surfing) by virtue of an increased waterline length when heeled.
Actually, CCA-era boats can sail at the hull speed for their increased waterline when heeled.... but generally not much more. IIRC, the calculation is actually fairly accurate, but you have to take into account the extended waterline length.
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  #14  
Old 07-03-2007
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As Seabreeze stated, your LWL increases as you heel, thereby increasing your "theoretical" hull speed.
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Uhhhh, hey dog......
This is from an article on the (Ted) Brewer 31/32. Note especially the next-to-last sentence.

CCA INFLUENCE - The design was heavily influenced by Cruising Club of America (CCA) offshore racing rules. As such, they have narrow beams, a relatively heavy displacement, moderate ballast and the graceful overhangs that were prevalent among boats of the era. The result is a beautiful, sea-kindly boat that is initially tender, but which firms up once heeled. Heeling provides more hull in the water, and this additional waterline results in greater speed. She is given high marks for seaworthiness, has made several successful ocean crossings, and has weathered big storms.
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  #16  
Old 07-04-2007
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I was just clarifying that the increase in speed is due to the increase in waterline... unlike a boat that is surfing or planing or a multihull, which generally doesn't follow the SQRT LWL*1.34 rule.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
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—Cpt. Mal Reynolds, Serenity (edited)

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  #17  
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To clarify the Dog's point further, if needed, the CCA boat is, in fact, NOT sailing above hull speed. "Hull speed" may be different at different angles of heel, but it is still a derived function of LWL. To state that the boats can sail faster than hull speed, without surfing, distorts the actual architectural principle behind "hull speed".

"Hull speed" is a term used to describe the capabilities of displacement hulls. Those vessels that are able to, on occasion, surf are best considered as semi-displacement hulls at that point.

The CCA boats might then be classified as having a certain hull speed at their best point of reaching.
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  #18  
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Ok, for all the hair-splitters. Yes, when heeling it's still displacement. Would it be fair to say that when waterline is measured, it's on a static model with zero-degree heel? I've looked everywhere and can't find a boat listed with 30-degree heel angle waterline. Anyway, perhaps it will be more palatable if I say CCA boats were capable of sailing above their RATED hull speed by virtue of their increased waterlines when heeling.
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Now that would be "well stated".
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Ok with out using math, just theory. A sail boat being a displacement vessel can only travel as fast as the wave length created from the bow to the stern, being the LWL as a sail boat heels the LWL is increased, extending the wave length allowing the vessel to exceed its hull speed. the longer the wave length the faster the boat.
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