In a message dated 09-12-95 ED DEBEE wrote to  ALL:
 ED> The following is quoted from "Boating Facts and Feats" by Peter
 ED> Johnson...
 ED> "An accepted measure of speed in displacement vessels (as opposed to
 ED> planing craft) is the ratio of velocity, "V", to the square root of
 ED> the load waterline, (SR) "L".  The speed/length ratio is V/(SR)L.
 ED> This is an empirical ratio and the maximum achieved in conventional
 ED> craft is usually in the region of 1.4. But this depends on the many
 ED> facets of the design of any particular boat and the maximum may be
 ED> lower or as high as 1.7.  The value of the speed/length ratio is as a
 ED> comparison within generic types of craft."
Boy, this  blows a lot that I've learned out the window, but DOES explain wh 
our 28' Tanzer (6.6 calculated hull speed) cruises close-hauled between 7.5 
and 7.8 in 15-25 knot winds (110% + double-reef). [Hopefully will soon 
replace the 24-year-old sails and see what she can _really_ do . They're 
so blown out that the only thing that flattens the main is reefing and I've 
broken 3 wire halyards trying to get the genny under control.]
Does Mr. Johnson offer any more information about the statement? Know where 
to get the book? Is it worth getting (beyond that explanation -- which may b 
worth the price of admission, itself)?
I was taught that 1.34 * Sqrt(LWL) was the LAW! (surfing excepted, of course 
A big enough wave will make ANYTHING exceed hull-speed). Calculating 
backwards, that means our boat, with a 23'6" LWL has a Speed/Length Ratio 
(SLR?) of at least 1.61, but WHAT CAUSES THE CHANGE? My understanding was 
that the hull speed was a factor of the length of the wave caused by the 
boat's movement through the water. Trying to make the water do what it didn' 
like to do required excessive force. For some reason, I thought the cause wa 
drag at the stern. Trying to go faster just squatted the transom further and 
further. The length of the wave seems like it should be constant... water 
will rise and fall and rise again at a constant pace...
AHAH! I think I have it! The length of a wave is proportional to its height! 
If boat "A" generates a smaller wave than the same-sized boat "B" at a given 
speed, the wavelength will be that much smaller.
Gawd! I can visualize this all, but re-reading it sounds flakey even to me. 
Anyone got a text that really explains this stuff?
In the meantime, next season I'm going to see how fast I can drive the boat 
while motor-sailing. I think that knowing the boat's true hull-speed is 
safety feature.
Jere
 -> Alice4Mac 2.4.4 E QWK Eval:02Dec95
Origin: "Xan-a-Deux", based in Georgetown, MD
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