A couple of newbie questions
 

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.

A couple of newbie questions
 

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

A couple of newbie questions
 

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

A couple of newbie questions
 

On Sat, 17 Jan 2004 22:20:54 GMT, "Calif Bill"
wrote:


"Joe Parsons" wrote in message
.. .
[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


Difference between an engineer and a mathematician.

Voluptuous Dallas Cheer leader is standing nekid on the goal line.
The engineer and math nerd are on the other line. Told that the first one
to her gets her. Only restriction is can move only 1/2 the distance to the
goal in any one move. Math nerd says 'won't even start, is an infinite
series and will never get there.'. Engineer is moving and states, 7 moves
and I am close enough for any thing I want to do.

Joe, you a math minor in a business major?

I don't know about Joe, but I are both - or am was that is. ;)

Later,

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

St. Pete, 12 Lb. Test

A couple of newbie questions
 

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

A couple of newbie questions
 

I like that explanation - simple yet complete.

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

A couple of newbie questions
 

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.

A couple of newbie questions
 

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

A couple of newbie questions
 

On Sat, 17 Jan 2004 18:37:56 -0500, Gene Kearns
wrote:
Jax,

Please go back to your doctor for a stress test. 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.....

========================================

Where's "Bertie the Bunyip" when we need him?

A couple of newbie questions
 

"Joe Parsons" wrote:

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


[HAIRSPLITTING=ON]

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]


[HAIRSPLITTING = ON AGAIN]

Actually, the statement, "A nautical mile is also, precisely, 6,076.12
feet."
IS precise. It may not be exact, but it is precise.

[HAIRSPLITTING = OFF]