What is hull speed and how do you figure it?

[Brian]

What is hull speed defined?
Is this equation correct? (square root of LWL x 1.3)
Thanks

[Daryl Miglia]

What is hull speed defined?
Is this equation correct? (square root of LWL x 1.3)
Thanks

I was of the understanding it was (square root of LWL x 1.4) but I could be mistaken.
Daryl



dmiglia@gwe.net

[Tom Coons]

What is hull speed defined?
Is this equation correct? (square root of LWL x 1.3)
Thanks

I was of the understanding it was (square root of LWL x 1.4) but I could be mistaken.
Daryl

Norman L Skene's book "Elements of Yacht Design" defines hull speed (p, 6) as 1.25 times the square root of the water line length. That's in knots which of course is 1.2 miles per hour.

In terms of definition, it's the speed at which a boat moves easily through the water. Above that speed a large stern wake develops which sucks the boat back and slows her down. As you try to go faster the resistance increases and it gets harder and harder to go just a little faster. Sometimes you can exceed it with overwhelming force such as hurricane force winds or huge motors but it becomes very inefficient. It's relatively easy to get a boat up to hull speed, but difficult to exceed it except with overwhelming force.



TacCambria@thegrid.net

[Catherine Monaghan]

Here's a website that will help you figure out the maximum hull speed, displacement to length ratio, sail area/displacement ratio, and capsize screening formulas for your boats: <a href="http://eightsea.com/eightsea/boatcalc.shtml">The Eighth Sea Boat Calculator</strong></a>

What is hull speed defined?
Is this equation correct? (square root of LWL x 1.3)
Thanks

catherine_monaghan@merck.com

[Jon]

What is hull speed defined?
Is this equation correct? (square root of LWL x 1.3)
Thanks

Boats move through the water by either displacing water or by planning on top of it. Most sailboats are displacement boats. As a displacemnt boat increases speed, the wakes get bigger and further apart and the bow wake gets bigger, creating more resistance. This affect is exponential, so as one approaches a theoretical sort of maximum, the energy needed to increase speed even a little get very great. If you get enough power, you can plain, but this is unlikely from sail power in a larger boat. Hull speed will vary a bit based on the boat's design, but the formulas presented are good guesses for most boats.



Jon_45@hotmail.com