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post #82 of Old 11-26-2012
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Cool Re: Starrett-Jenks Morgan45 info-opinions

Just returned from some work on ORION -- installed hawse pipes and ancjhor rode reel winches. I'd like to post pictures but haven't figured out how to do it.

Judy, are you in San Francisco Bay?

Azi: You have repeated an oft misunderstood myth about waterline and heeling. Don't feel bad -- even the magazine writers usually get this wrong. The one exception I remember is "Lee Helm" in Latitude 38 who explained it correctly. As follows, more or less. The overhangs are there because they do let the effective waterline get longer as they are immersed, HOWEVER, it is NOTdue to HEEL. Indeed if you heel any of the kind of boats we are talking about in still water and at rest, the waterline gets Shorter as the relatively stiff bilge is immersed. What actually happens is due to wavemaking and speed through the water. When a boat is moving at close to hull speed (1.4*sqrt(Lwl)) it creates a wave system with a deep trough about midships, crests at bow and stern. As a boat with long overhangs settles into this depression the effective waterline length increases because the long ends are now riding on the bow and stern waves. In our IOD, for example, the transom at the end of the counter is about two feet above the water and about five feet abaft the end of the resting Lwl. But at speed the transom is at the waterline and the whole of the counter overhang has become part of the submerged body of the boat. Same at the bow but to a lesser extent. The displacement remains the same because the midsection is no longer immersed as deeply due to the depression or trough of the induced wave.

To put it another way, the motion of the boat throught the water cuses the water surface to become bent in the region of the boat. A boat with long overhangs is designed to have a long and optimal form when sailing on this bent surface.

It has nothing to do with heel (except that sailboats generally do heel, when going fast,) the same thin happens going dead downwind with little or no heel.

OK, sorry for the rant -- I just would like to get the sailing community to get this right.
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