Natural Speed - Page 2 - SailNet Community
Old 04-11-2008
&amp;quot;Nevis Nice&amp;quot;

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My average speed over ground, as measured by my GPS, for any given year's cruising on the Cheasapeake was 5.6 kts. This was a combination of sailing in varied wind conditions and motoring. When motoring, I got into the habit of setting the rpms at "what felt right" for the boat.

I had never heard of "Natural Boatspeed". Using the formula, the Natural Boatspeed for my boat is 5.6 kts. A coincidence??? It looks to me like we were "in the goove".

Hud
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Old 04-11-2008
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Natural speed is equal to sqrt (lwl). Hull speed is equal to 1.34 * sqrt (lwl). IIRC, one indicates the approximate point at which the curve for power vs. boat speed goes from linear to geometric, the other where it goes from geometric to exponential.

Basically, once a displacement hull is at hull speed, all putting additional power to the boat is going to do is cause the boat to squat for the most part. At natural speed, increasing power will result in diminishing gains in boat speed.

Quote:
Originally Posted by xort View Post
How is this different than hull speed?

Sailingdog

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Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 04-11-2008
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Quote:
Originally Posted by xort View Post
How is this different than hull speed?
Hull speed is the Max speed a displacement hull can go before it starts surfing. Or in other terms over running it's bow wake. which in the case of the boat I was taking about in my first post is a little more than 9 kts. of boat speed.
bubb2 is offline

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