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Go Back   SailNet Community > Out There > Cruising & Liveaboard Forum > Living Aboard
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  #11  
Old 04-11-2008
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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".
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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?
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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.
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