Catenary Effect on Horizontal Pull, Yaw and Damping

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NormanS said:
Logic on a sailing forum! Ha.

Contrary thoughts, yes, if only to point out the absurdity of your suggestion about the effect on catenary of towing against the force of the tide.
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I mentioned the tide and wind in relation to a static anchoring situation where a catenary is seen to exist against an opposing force of tide and or wind perhaps you can understand that. Perhaps not.
 
In a static (real) situation there will always be sag in the line. You would need infinite tension or weightless line to do otherwise.
Anchoring or towing, however, are most certainly not static situations. As the tension increases the line will straighten, if it does so fast enough the momentum will permit the line to go straight. If that does happen the the load will also have significant momentum away from the anchor. As far as loading goes, what happens next is really quite ugly and liable to rip bits off load and anchor unless there is some snubber arrangement. Mixed rode with deliberately stretchy bits is an ideal set up. If, however the changing load is never sufficient to generate enough momentum in the line to let it straighten then the sag in the line will provide adequate snubbing.
 
Fr J Hackett said:
looking at it logically:rolleyes: To have a catenary and be able to tow something or for that matter retain a catenary against an opposing force be it tide wind or both then the force applied to achieve that state must be less than the force required to lift and straighten the weight of the cable.
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You can't completely lift and straighten a cable in the real world, there will always be some catenary, so basically you just said - "the force to have a rubber band stretched a bit must be less than the force required to stretch a rubber band a lot."

Certain logic in there ;)
 
Minn said:
In the case of deepsea towing, the catenary and the snubbers are both there to provide damping; the catenary is the primary damper and the elasticity of the nylon only comes into play once the "spare catenary" has been used up or if the tow is shortened up for shoal water.

I think we need to distinguish between the catenary that is always there and what I want to call "spare catenary" - such as a length of chain lying on the bottom, or a weight sitting on the bottom.
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I think we need to use proper definitions of 'catenary', 'damping' and 'elasticity'.
 
GHA said:
You can't completely lift and straighten a cable in the real world, there will always be some catenary, so basically you just said - "the force to have a rubber band stretched a bit must be less than the force required to stretch a rubber band a lot."

Certain logic in there ;)
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Why can't you completely straighten a cable?
 
Fr J Hackett said:
Why can't you completely straighten a cable?
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Just the way the universe is. :)

Or think of similar set up, tie a 100' long rope to a gate post, hang a bottle of beer at the centre and the pull the rope and try to make it horizontal.
You'll never get it straight, maybe quite close before the rope breaks but never all the way.
 
GHA said:
Just the way the universe is. :)

Or think of similar set up, tie a 100' long rope to a gate post, hang a bottle of beer at the centre and the pull the rope and try to make it horizontal.
You'll never get it straight, maybe quite close before the rope breaks but never all the way.
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Pull fast enough and the rope wont just go straight, the bottle will go over the house.
 
Is the anchor chain really curved, or is this an illusion created by gravity producing a curvature of space/time? :) :).
 
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noelex said:
Is the anchor chain really curved, or is this an illusion created by gravity producing a curvature of space/time? :) :).
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Nice try but.... Jif it were space/time curvature that caused an apparent bend then the bend wouldn't be apparent since light would be bent too.
Its more likely to be atmospheric lensing, which also makes the world appear flat.
 
As the chain gets closer to straight, there is less and less ability for it to absorb any shock. When the whole chain is lying on the bottom and goes vertically up to the anchor roller, the boat can surge back quite a bit before it stops. Once the chain is entirely off the seabed, the boat might only be able to go back a meter or so. So higher shock loads.

As an aside, I was once involved in the alignment of ships' propellor shafts. That used to be done with piano wire stretched tight - from the coupling to the P bracket or propellor boss. That wire was stretched as tight as you can imagine - and in order to ensure a proper alignment, the catenary was calculated and accommodated.
 
Fr J Hackett said:
Glad to see we are getting down to the real physics of the matter.
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For far too long, anchor threads have used simplified Newtonian mechanics.

Using the more correct quantum theory I predict there will be widespread consensus from now on.

Others might suggest anchors are too large for quantum mechanics to be relevant, but some posts on YBW are already recommending very small anchors. I don't think it will be long before a single (new generation) subatomic particle will be felt suitable to anchor even larger boats, although attaching the chain to such an anchor might cause some issues.

If nothing else, I am sure everyone will agree that the existence of multiple universes helps explain some anchor posts :).
 
noelex said:
For far too long, anchor threads have used simplified Newtonian mechanics.

Using the more correct quantum theory I predict there will be widespread consensus from now on.

Others might suggest anchors are too large for quantum mechanics to be relevant, but some posts on YBW are already recommending very small anchors. I don't think it will be long before a single (new generation) subatomic particle will be felt suitable to anchor even larger boats, although attaching the chain to such an anchor might cause some issues.

If nothing else, I am sure everyone will agree that the existence of multiple universes helps explain some anchor posts :).
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Well that would put paid to your wonderful photographs :)

Your quantum anchor could be thought of as being hooked into every piece of seabed possible........ as long as you don't look at it ;)
 
GHA said:
Well that would put paid to your wonderful photographs :)

Your quantum anchor could be thought of as being hooked into every piece of seabed possible........ as long as you don't look at it ;)
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I have tried catting the anchor as a solution to this problem but I find it leads to a marked degree of uncertainty so far as I can C.
 
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