On Sat, 17 Jan 2004 17:30:05 -0500, DSK wrote:

Lou Dempster wrote:

Could someone please tell me what a knotical mile is in comparison to
the standard mile. Also what does D/L limited speed: 10.08 kt. and
Disp. Hull Speed: 5.90 kt. mean.
I am just fooling around with a hull designer and would appreciate any
info.

Well, other have answered the nautical mile question, so I'll try the
other two. Displacement hull speed is the highest speed a given hull can
reach when limited to it's wave train. What this means is that the boat is
fully supported by displacement of water (as opposed to planing, where the
boat is supported by hydrodynamic force of water going by under the hull)
and so therefore it has to push water out of the way, making waves. A less
obvious point is that the water has to come back together again as the
boat passes.... in traditional hull design, the key to designing a fast
boat was always said to be to minimize the stern wave.

Displacement hull speed is determined by waterline length. The further
apart the bow & stern waves are, the faster the connected wave train can
move across the surface. At 5.9 knots, the crests of the bow and stern
wave are about 18' 4" apart, so I bet that is the waterline length of the
hull you are designing.

D/L refers to the displacement/length ratio, which can affect whether the
boat is truly limited by it's wave train. A long skinny hull can go faster
relative to it's theoretical hull speed, that's how catamarans and Navy
destroyers reach higher speeds.

Hope this helps.

I like that explanation - simple yet complete.

Nice.

Later,

Tom
S. Woodstock, CT
----------
"My rod and my reel - they comfort me."

St. Pete, 12 Lb. Test