Hull speed

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therobesons

therobesons

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Jun 7, 2009
116
Hunter 1999 Passage h420 CC Oceanside
Anyone know the hullspeed for a 1999 Hunter 420 passage CC with a 37' waterline?

Also what is the formula?

Thanks
 
therobesons

therobesons

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Jun 7, 2009
116
Hunter 1999 Passage h420 CC Oceanside
Thanks buck420

It works out to be 8.15
Less than i thought as our trip from San Diego to Portland Oregon we gave passed 9 kts many times with just stock sails
I can do 8 plus with engine alone at wot
Maybe I calculated it wrong
 
justsomeguy

justsomeguy

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Feb 20, 2011
8,062
Island Packet 35 Tucson, AZ/San Carlos, MX
Maybe that's why it's called "theoretical" hull speed.
 
O

oldersalt

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Aug 10, 2011
37
none none Northern California
Hull speed is not an absolute limit. It's the speed above which the energy needed to make the boat go faster starts to increase very rapidly. It's the speed at which the bow wave wavelength starts to approach the waterline length of the boat. As the bow wave wavelength increases, the boat actually settles deeper into the water and has to push more water out of the way. So you can often motor faster than the hull speed, but your fuel consumption will probably drastically increase. And it is certainly possible to sail somewhat faster than hull speed in the right conditions. But remember, in the old days of sail, big sailing ships hit by squalls were sometimes "driven under" and sunk before the crew could get enough sails off (but really unlikely to happen with modern sailboats). If you are motoring through really thin water at high speed, remember that your draft will actually increase by several inches.
Enjoy!
Oldersalt

"In theory, theory and practice are the same. In practice, they are not."
 
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oldersalt

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Aug 10, 2011
37
none none Northern California
And another thing...when you are heeled over, the waterline length of the boat probably increases by a foot or maybe more, thus increasing the theoretical hull speed. Basically, there are so many variables in all this you can pretty much just forget about it, except as a VERY theoretical exercise.
Oldersalt
 
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