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.

Fresh Breezes- Doug King

Hope this helps.

Fresh Breezes- Doug King


it would help, doug, if it weren't bull****, all based on a couple assumptions
that are not hardly true, i.e. a boat *must* go over a wave rather than through
it, and that mathematically a sine function explodes at zero degrees.

but it sounds good, because it -sounds- like hard science. just like in one of
the only three books ever written about sailing states.

JAXAshby wrote:


but it sounds good, because it -sounds- like hard science. just like in one of
the only three books ever written about sailing states.

Jax, we need a good laugh. Why don't you explain hull speed for us?

DSK

Why don't you explain hull speed for us?

DSK

it doesn't exist in any fashion as a scientific "limit", so there is nothing to
explain, scientifically.

psychologically, on the other hand, want easy answers to complex issues so will
believe most anything handed to them.

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

I like that explanation - simple yet complete.

also wrong, but what the hey it is simple and complete.

On 17 Jan 2004 23:17:07 GMT, (JAXAshby) wrote:

I like that explanation - simple yet complete.

also wrong, but what the hey it is simple and complete.

Where exactly is it wrong?

Later,

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

St. Pete, 12 Lb. Test

also wrong, but what the hey it is simple and complete.

Where exactly is it wrong?


among other things, there is no reason whatsoever that a boat MUST go over top
of a wave rather then through it, and a sin function does NOT explode at zero
degrees.

gene, be stupid if that's what you want. who cares.

Obviously, since you
are *so* much more intelligent that we are and we have nothing to
contribute to your most important life, it would be best if you went
back to where you were for the most of 2003... (away from here).

Lest you forget that we are dirt under your feet and nothing but an
irritant destined to spoil your cardiovascular health, please re-read:

http://tinyurl.com/2uuuc

Then go back......

Byeeeeeee.....
--



Grady-White Gulfstream, out of Southport, NC.

http://myworkshop.idleplay.net/cavern/
Homepage
http://www.southharbourvillage.com/directions.asp Where
Southport,NC is located.
http://www.southharbourvillage.com/autoupdater.htm Real Time Pictures
at My Marina
http://www.thebayguide.com/rec.boats
Rec.boats at Lee Yeaton's Bayguide
http://www.cafeshops.com/recdotboats
Shameless Commercial Plug for Lee's Rec.Boats Clothing

On 18 Jan 2004 13:17:34 GMT, (JAXAshby) wrote:

also wrong, but what the hey it is simple and complete.

Where exactly is it wrong?

among other things, there is no reason whatsoever that a boat MUST go over top
of a wave rather then through it, and a sin function does NOT explode at zero
degrees.

Really?

I can think of a thousand reasons why a boat MUST go over a wave,
however I can only think of one reason why a boat MUST go through a
wave and that is if it is heavier than water and is capable of passing
through a wave.

Later,

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

St. Pete, 12 Lb. Test