Max speed

[pugwash]

Maximum theoretical speed of a displacement hull is the square root of the waterline length times 1.4. Right? Or is it 1.25? Or are both wrong?

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[jamesjermain]

Both or neither could be right.

The figure of 1.4 is taken as a constant for modern easily driven fin keeled hulls. In years gone by long keelers were usually calculated using 1.25 or 1.3. An open class racing yacht can achieve 1.5 or even 1.6.

Catamaran and trimaran hulls are slim enough not to be governed by wave resistance in the same way as monos so the formula does not apply

<hr width=100% size=1>JJ

 

[pugwash]

Thanks for that. How would you rate a Holman like mine, slightly longer but also tubbier than a Twister? Say 1.3?

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[global_odyssey]

Nanni Diesel's site has a maximum hull speed and HP required calculator - to determine what power will reach your hull speed - needs W/L length, and gross weight.- See http://www.nannidiesel.com/eintro.htm

Might be useful?

<hr width=100% size=1>I've got wind......................
...............................in my sails!

 

[Jeannius]

James...

Are you sure about your comments on cats/tri's? I seem to remember reading, many years ago (probably in YM) that the formula applied to everything where the hull width was greater than 6% of the waterline length. Might have been Nigel Irens speaking.

Mike

<hr width=100% size=1>Mike

<A target="_blank" HREF=http://www.sailbvi.net>www.sailbvi.net</A>

 

[snowleopard]

6% is overstating it, 1/8 is nearer the mark. it also depends on whether the hull form creates waves, for example the catalac builds a big bow wave because of its underwater shape so definitely has a max hull speed while other cats of similar length and beam don't.

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[polarity]

For a full and technically detailed explanation by the late Mike D see this post at boatdesign.net

<A target="_blank" HREF=http://boatdesign.net/forums/showthread.php?t=1220>http://boatdesign.net/forums/showthread.php?t=1220</A>

Paul

<hr width=100% size=1>Paul
<A target="_blank" HREF=http://www.polarity2.com>http://www.polarity2.com</A>
OSTAR 2005

 

[oldharry]

1.4 x square root of W/L was the formula used when I was a lad - building the Victory etc.....

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