Catenary Effect on Horizontal Pull, Yaw and Damping

  • Thread starter Thread starter Deleted member 36384
  • Start date Start date
noelex said:
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.
Click to expand...

Good point. Must be the Higgs boson, since it gives all other particles, and anchors, their mass...

Mike.
 
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."
Click to expand...

Which is actually not true, and explains why the pressure required to inflate a balloon falls as the balloon gets bigger.
 
JumbleDuck said:
Which is actually not true, and explains why the pressure required to inflate a balloon falls as the balloon gets bigger.
Click to expand...

It does and it doesn't.
The tension in the skin of a balloon is proportional to the radius as well as the pressure, so even if the rubber didn't get thinner and weaker, the pressure to stretch it would still fall...
 
lw395 said:
It does and it doesn't.
The tension in the skin of a balloon is proportional to the radius as well as the pressure, so even if the rubber didn't get thinner and weaker, the pressure to stretch it would still fall...
Click to expand...

Strangely the same applies to soap bubbles, even though the surface tension is constant. And the reason why microscopic bubbles contain high pressures and chains of bubbles form on imperfections in your champagne glass...

Mike.
 
lw395 said:
It does and it doesn't.
The tension in the skin of a balloon is proportional to the radius as well as the pressure, so even if the rubber didn't get thinner and weaker, the pressure to stretch it would still fall...
Click to expand...

But as the balloon gets bigger, the radius increases....

You're quite right, though, that the high Poisson's Ration (~ 0.5) of rubber matters, as does its rather odd stress strain curve.
 
Rogershaw said:
I can vaguely remember from long ago university days that mathematically it would need an infinite pull on the ends of a catenary to pull the catenary completely straight
Click to expand...

Instead of the infinite pull you could just use a neutrally buoyant anchor line.
 
Lon nan Gruagach said:
Dynamically adjusted for changes in water temperature and salinity. Ohh, with zero cross section so drag won't deflect it.....
Click to expand...
Of course:), but the water is a uniform temperature,salinity and density in my example so that is easy. There are no variations in the gravitational force. There is no need to worry about the cross sectional area. There will be no drag because the rope is not moving and there is no current. The rope is quality stuff and is perfectly uniform.

I am very picky where I anchor and my anchoring gear:).
 
Last edited:
mjcoon said:
I wish I could think of a reason to squeeze the space elevator concept in here...

Mike.
Click to expand...

Anchoring your spaceship in orbit, such as securing it to the space station, but you will need a good new generation anchor to set with no gravity :).
 
Last edited:
Honestly, it was just idle summer holiday musings, addressed on the first reply.

Another lazy musing. Yesterday I was returning from Saint Tropez and there were two very large cruise liners at anchor (also one anchored off Saint Raphael). It was the usual Afternoon Force 4 and the ships had rotated about 90 to 120 degrees on their rodes, single anchor. The anchor chain was not straight up and down and comparing the size of the stored anchor to the area of ship and mass of ship, I would consider them to be grossly undersized on anchors, especially considering that they are old generation style stockless types (not sure what type they were). Now, I think of a vastly smaller semi submersible drilling rig with either Danforth or Bruce style anchors and they are massive compared to these cruise liner anchors. None of them were dragging. I don’t see how the anchor can work.

I now wonder if weight of chain is far more important that anchors.
 
BlowingOldBoots said:
Honestly, it was just idle summer holiday musings, addressed on the first reply.

Another lazy musing. Yesterday I was returning from Saint Tropez and there were two very large cruise liners at anchor (also one anchored off Saint Raphael). It was the usual Afternoon Force 4 and the ships had rotated about 90 to 120 degrees on their rodes, single anchor. The anchor chain was not straight up and down and comparing the size of the stored anchor to the area of ship and mass of ship, I would consider them to be grossly undersized on anchors, especially considering that they are old generation style stockless types (not sure what type they were). Now, I think of a vastly smaller semi submersible drilling rig with either Danforth or Bruce style anchors and they are massive compared to these cruise liner anchors. None of them were dragging. I don’t see how the anchor can work.

I now wonder if weight of chain is far more important that anchors.
Click to expand...

I've wondered that about large ships generally - size for size they all seem to have titchy anchors, including naval ships. Do they perhaps assume that they'll use engine as well in anything of a blow?
 
BlowingOldBoots said:
Honestly, it was just idle summer holiday musings, addressed on the first reply.

Another lazy musing. Yesterday I was returning from Saint Tropez and there were two very large cruise liners at anchor (also one anchored off Saint Raphael). It was the usual Afternoon Force 4 and the ships had rotated about 90 to 120 degrees on their rodes, single anchor. The anchor chain was not straight up and down and comparing the size of the stored anchor to the area of ship and mass of ship, I would consider them to be grossly undersized on anchors, especially considering that they are old generation style stockless types (not sure what type they were). Now, I think of a vastly smaller semi submersible drilling rig with either Danforth or Bruce style anchors and they are massive compared to these cruise liner anchors. None of them were dragging. I don’t see how the anchor can work.

I now wonder if weight of chain is far more important that anchors.
Click to expand...

Common more modern anchors on current commercial vessels would be an AC 14.

http://www.sotra.net/products/anchors/high-holding-power-anchors/ac-14

I would agree, in common with many, their anchors seem small but equally they don't seem to drag (apart from spectacular failures). I spoke with one commercial Captain who anchored in a fairly exposed roadstead with a 10t AC 14. His concern was not dragging but damaging the 'chain lock', which is simply a large version of 'our' chain lock - a big bit of steel levered into the hole in the chain. His solution, retrieve anchor, and simply set limits in the bay within which he was comfortable, motor to windward, drift back, motor to windward and drift back - until the wind and seas eased. He did not suggest excessive use of chain (in term of length) - but commercial chain are undoubtedly beefy - but how they scale to ours, don't know.

Interesting question as commercial ships do seem to have large windage - but they don't veer 'aggressively' nor do they 'snatch'.

Jonathan
 
I have been watching a coastal gravel carrier anchored outside Kalymnos, where the wind is blowing F6-7 according to forecast. The ship is yawing well over 90 degrees over a period of 5-10 minutes.

An aircraft carrier deck officer told me they always dragged in any wind. A midshipman was stationed in the bow to watch and when dragging had reached a certain point they would up anchor and steam back to where they started.
 
vyv_cox said:
I have been watching a coastal gravel carrier anchored outside Kalymnos, where the wind is blowing F6-7 according to forecast. The ship is yawing well over 90 degrees over a period of 5-10 minutes.

An aircraft carrier deck officer told me they always dragged in any wind. A midshipman was stationed in the bow to watch and when dragging had reached a certain point they would up anchor and steam back to where they started.
Click to expand...

"Always dragged in any wind" That seems a bit pathetic. Maybe their anchoring technique was less than perfect. :D
 
You must log in or register to reply here.

Share this page

Top