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post #12 of Old 07-27-2012
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Re: How do you measure the waterline

Rbrasi, I see that you are from Henderson and I assume you sail in Lake Mead. Is there much river current in the lake? What is your drift rate on a calm day – you could use that as a constant to adjust from speed over ground to boat speed. Don’t get too hung up over theoretical boat speed (THS). After all, it is theoretical and was developed in the age of square riggers which we all can agree have an entirely different hull form. The basic principal is displacement boats have to push water out of the way to move, and after a certain point, they can’t push the water away any faster. As you approach THS, a standing wave will develop at the bow and the stern. In effect leaving your boat in a “hole” between the two. At that point, it requires an enormous amount of energy to pull your boat out of that “hole”. This is when power boats step up onto a plane. About the only way you can do this in a sailboat is to surf a wave or in your case, a wake. Unfortunately you need something along the line of 10-15 kts of boat speed to sustain a surf so for guys like us, the thrill is fleeting. Use your THS speed as a bench mark, kind of like breaking the sound barrier and don’t stress if you aren’t matching it all the time.
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