11 Sep 95, Richard Wheet writes to Ed DeBee:
Richard,
Thanks for the reply.  In response I quote a paragraph from the book "Boating 
Facts and Feats" by Peter Johnson.  The quote will follow our posts for 
continuity of thread.
Ed said:
 >> Enjoy the posts on boat speed.  I would add that the standard formula of
 >> 1.34 times square root of waterline length is only an average.  For
 >> instance, my Precision is a semi-flat bottomed hull with shoal draft
 >> keel.  Computed hull speed is 5.95 knots.  However, if the heel is kept
 >> at 15 deg. and the wind is on some part of the beam, I can usually hold
 >> 6.2 knots.  This is due to the hull starting to rise up in the water,
 >> reducing the wetted surface drag. Downwind, with gusts and surfing, we
 >> have seen 9.2 knots.  But this skipper doesn't like the feel of the
 >> helm.  Tricky.
 RW> Remember that the formula is for THEORETICAL boat speed... under the
 RW> assumption that the boat cannot pass over its own bow wave... what you 
are
 RW> describing is called "hydroplaning"....
 RW> THEORETICAL is not an average... it is the max speed under normal keel
 RW> conditions....
The following is quoted from "Boating Facts and Feats" by Peter Johnson...
"An accepted measure of speed in displacement vessels (as opposed to planing 
craft) is the ratio of velocity, "V", to the square root of the load 
waterline, (SR) "L".  The speed/length ratio is V/(SR)L.  This is an 
empirical ratio and the maximum achieved in conventional craft is usually in 
the region of 1.4. But this depends on the many facets of the design of any 
particular boat and the maximum may be lower or as high as 1.7.  The value of 
the speed/length ratio is as a comparison within generic types of craft."
I thought you might find this interesting.
Ed
Skipper of Revelation
V/(SR)L = 1.39
--- GoldED 2.40
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