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genei, knock it off. you have no idea what the mathematical term catenary
means, nor any idea of the physics behind it, and sure as hell no understanding
just how ******************VERY***************** quickly the forces can become
HUGE.
go sleep it off.
"Gene Kearns"
Date: 9/20/2004 10:36 AM Eastern Daylight Time
Message-id:
On Sun, 19 Sep 2004 00:10:39 GMT, Short Wave Sportfishing
wrote:
On Sat, 18 Sep 2004 19:46:04 -0400, Gene Kearns
wrote:
On 18 Sep 2004 21:15:33 GMT, (JAXAshby) wrote:
What happens during the interaction of forces on the rode would be
most fascinating.
a way to simplified look at it is to consider the chain/rode/line to have
zero
weight pulled between two points (say 100 feet apart), then hang a 1#
weight in
the center point and check how much strain it put on the end points when
the
weight hangs 20 feet, then 10 feet, then 5 feet, then 1 foot, then 1 inch,
then
1/10th inch. Just use trig to figure the forces.
So.... we just used intuitive trig to figure out why (1) we use scope
with an anchor and (2) why we don't tie boats to the dock with chain.
Now *that* is some real science......
And your "simplified look" does not apply.... an anchor rode does not
employ both ends at the same "Y" value.... therefore assumptions of
Y=Y'=0 do not obtain and is, therefore, the root cause of your lack
of understanding in this area. There isn't *anything* *attached* to
the middle.
But wouldn't the strain be equal at the arthimetical center and can be
equated to weight? It's really just another to figure energy
transfer, right?
I'm not totaly familiar with this so if I mess this up, it's an
electronic engineer with a math degree playing at mechanics, but
catenary defined means the shape of the line (or in this case rode) as
a curve. A funciton of strain would be weights at either end. Strain
can be defined as stored energy which is, I would think, distributed
evenly along the line to the end points. One way to define how much
strain is being applied would be to add weight to the middle and
measure the deflection.
At that point, it becomes a trig function - yes/no?
Yes. My point is that Jax keeps talking about this particular catenary
(and if properly applied, it isn't truly a catenary) as though both
ends are supported and hanging.... they aren't. The point of the
anchor rode is to fall from the boat at some small angle and end up at
the anchor at least parallel to the sea bed.
*
*
*
*
*
*
*
*
*
*
*
*
*********************ANCHOR
Don't know if this "graphic" will work, but this is what one should
have, not a true catenary..... if this is expected to hold the
anchor.
the forces get out of hand ********VERY******** quickly. Even worse, is
that
the weight in the middle (or chain) has momentum as the boat rocks, so the
"natural" position of the weight overshoots and makes for seriously high
g-loads.
There is no weight "in the middle" (other than the weight of the rode)
.... so you put two anchors on the same rode? Odd.
Using that concept, most people use kellets and think it is a good and
useful idea.
What's a kellet?
A kellet is "that weight" we've been talking about. If you don't
incorporate "the weight" in the anchor rode, via chain, it can be
artificially applied by using a kellet. Weight is what makes the
catenary functional. As the following link describes, once the
catenary is pulled tight enough to start lifting the shank of the
anchor, the holding ability of the anchor *rapidly* decays. The
greater the weight of the rode, the more holding power and (within
reason) the more shock absorbing power .
see:
http://www.anchorbuddy.co.nz/index.html
Later,
Tom
--
Grady-White Gulfstream, out of Southport, NC.
http://myworkshop.idleplay.net/cavern/ Homepage
http://www.southharbourvillageinn.com/directions.asp Where Southport,NC
is located.
http://www.southharbourvillageinn.linksysnet.com Real Time
Pictures at My Marina
http://www.thebayguide.com/rec.boats Rec.boats
at Lee Yeaton's Bayguide
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