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.

On Sat, 17 Jan 2004 09:45:54 GMT,
(Lou Dempster) wrote:

Could someone please tell me what a knotical mile is in comparison to
the standard mile.

A nautical mile is 6,080 feet (1853.18 meters) and is equal to 1/60th
of a degree of latitude. A statute mile is 5,280 feet.

Also what does D/L limited speed: 10.08 kt. and Disp. Hull Speed: 5.90 kt.
mean.

Just guessing here, but the D/L should be Displacement to Length Ratio
and don't aske me how you figure it because it has been a long time
and I'd have to look it up. However, it's basic explanation is that
the longer the boat at the waterline, the faster it is given it's
displacement (weight). For example, a boat weighing 1,000 pounds will
act like a boat weighing 2,000 pounds if you shorten the length at the
water line and vice versa - a 2,000 pound boat will act like a 1,000
pound boat if you lengthen the waterline. There are a couple of other
factors involved, but that's the basic gist of the term.

The Displacement Hull Speed is the speed at which the designed hull
will efficiently travel.

I am just fooling around with a hull designer and would appreciate any
info.

Have fun.

Later,

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

St. Pete, 12 Lb. Test

Short Wave Sportfishing wrote
A nautical mile is 6,080 feet (1853.18 meters)

Not quite. It is 1852 meters precisely.

On 17 Jan 2004 09:54:23 -0800, (Pat Norton)
wrote:

Short Wave Sportfishing wrote
A nautical mile is 6,080 feet (1853.18 meters)

Not quite. It is 1852 meters precisely.

Correctomundo.

Later,

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

St. Pete, 12 Lb. Test

On Sat, 17 Jan 2004 19:51:22 GMT, Short Wave Sportfishing
wrote:

On 17 Jan 2004 09:54:23 -0800, (Pat Norton)
wrote:

Short Wave Sportfishing wrote
A nautical mile is 6,080 feet (1853.18 meters)

Not quite. It is 1852 meters precisely.

Correctomundo.

~~ continued from hitting the wrong key and sending early ~~

A nautical mile is also, precisely, 6,076.12 feet.

I look at it this way - if I can get within four feet of something, I
can holler at it. :)

Later,

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

St. Pete, 12 Lb. Test

[HAIRSPLITTING=ON]

On Sat, 17 Jan 2004 19:57:18 GMT, Short Wave Sportfishing
wrote:

A nautical mile is also, precisely, 6,076.12 feet.

That's not precise--that's rounded to two decimals.

A nautical mile is, by definition, precisely 1,852 meters, as mentioned above.

That converts to 6,076.11549 feet (which still is not precise!).

[HAIRSPLITTING=OFF]

I look at it this way - if I can get within four feet of something, I
can holler at it. :)

Now THAT is practical navigation!


Joe Parsons

Short Wave Sportfishing wrote:
On Sat, 17 Jan 2004 09:45:54 GMT,
(Lou Dempster) wrote:


Could someone please tell me what a knotical mile is in comparison to
the standard mile.


A nautical mile is 6,080 feet (1853.18 meters) and is equal to 1/60th
of a degree of latitude. A statute mile is 5,280 feet.


Also what does D/L limited speed: 10.08 kt. and Disp. Hull Speed: 5.90 kt.
mean.


Just guessing here, but the D/L should be Displacement to Length Ratio
and don't aske me how you figure it because it has been a long time
and I'd have to look it up.

I looked it up:-) It's the displacement in tons, (not tonnes) divided
by, the cube of WL length in feet divided by 100.

D div (.01L)3

However, it's basic explanation is that
the longer the boat at the waterline, the faster it is given it's
displacement (weight). For example, a boat weighing 1,000 pounds will
act like a boat weighing 2,000 pounds if you shorten the length at the
water line and vice versa - a 2,000 pound boat will act like a 1,000
pound boat if you lengthen the waterline. There are a couple of other
factors involved, but that's the basic gist of the term.

Yes as Tom says, it's a predictor of surface area resistance.

The Displacement Hull Speed is the speed at which the designed hull
will efficiently travel.

The hull creates a bow wave & a stern wave, the speed of waves is
limited by the distance between crests, if the waves try to go too fast,
the crests get too close then the wave gets too steep & the crest
breaks. The generally accepted speed of waves before the crest breaks is
1.34 times the square root of the distance between crests (in ft).
(Admiral Taylor??) It's often expressed as 1.2 to 1.3 times when using
the sq rt of the boat's waterline length.

If you try to push a non planing boat faster than that, the nose lifts
up the back of the steep breaking bow wave & the stern falls into the
trough ahead of the steep breaking stern wave; save you have huge
amounts of power you'll be trapped, dragging ever steeper & bigger bow &
stern waves along, wasting power & fuel.

There is an exception, there's always a bloody exception:-) If the WL
length to WL beam ratio exceeds 11 then it seems to span or separate the
crests enough that the rule sorta doesn't apply (the bow & stern waves
are completely unrelated waves). e.g. long very skinny multihull hulls
seem to exceed their theoretical hull speed, so do things like
destroyers, some fast skinny ferries, without needing to actually get up
& plane.

A planing type hull can lift the stern, so with enough speed available,
allowing the bow to climb up & over the bow wave then break free, but
this takes some power initially to get the boat up out of the water &
skimming across the top.

K



I am just fooling around with a hull designer and would appreciate any
info.


Have fun.

Later,

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

St. Pete, 12 Lb. Test

If you aren't too fussy....a nautical mile is about 1 & 1/8th statute miles.
that is ...8 nautical miles = 9 road miles.

Lou Dempster wrote in message
...
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.

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.