Catenary Effect on Horizontal Pull, Yaw and Damping

[GHA]

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.

Similar came up in a thread ages ago and some links were posted, from memory big ships can't realistically carry the same size anchors as us compared to the size of the boat. So they expect to drag and run the engine in big winds, plus the chain drag on the seabed does help unlike us where it isn't on the seabed when the wind pipes up.

 

[vyv_cox]

"Always dragged in any wind" That seems a bit pathetic. Maybe their anchoring technique was less than perfect.

I assume you don't understand that the phrase "in any wind" means "in an appreciable wind". But I don't suppose the Royal Navy knows much about anchoring.?

 

[NormanS]

I assume you don't understand that the phrase "in any wind" means "in an appreciable wind". But I don't suppose the Royal Navy knows much about anchoring.��

Your assumption is incorrect. But to have a ship which cannot anchor successfully in an appreciable wind, is as I said, pathetic. I have no idea about the Royal Navy's anchoring procedures, but I'm sure there are people on here who may feel qualified to comment.

 

[Neeves]

I think somewhere the Classification Societies website it clearly state that their recommendations for anchor sizing is simply to allow a vessel to to wait for its place in a queue to enter port. Since the Pasha Bulker came ashore in Newcastle (Australia) the instructions have been altered for vessels anchored in the open roadsteads offshore. When there is a forecast of, I think its 25 knots, vessels are ordered off the anchorage and they must motor up and down the coast until the winds ease. This must make it all a bit busy as we have sailed past the anchored line of bulk carriers - and there has been as many as 40 waiting to load coal - with vessels also arriving and leaving

A Captain of a cruise ship has told if there is any chance of veering he will deploy 2, bow, anchors to try to stabilise the ship. It makes the tender service a bit easier. I'll qualify my comment about large vessels veering - they may veer but not with the speed of our yachts - though there will still be some real momentum at the end of the swing.

Jonathan

 

[JumbleDuck]

Your assumption is incorrect. But to have a ship which cannot anchor successfully in an appreciable wind, is as I said, pathetic.

Not necessarily. As others have pointed out, the anchors for big things which have to ride out bad weather are colossal, and quite impractical to carry or handle on most ships. Alternative strategies, like using the engine or steaming around, may be much more sensible.

 

[NormanS]

Not necessarily. As others have pointed out, the anchors for big things which have to ride out bad weather are colossal, and quite impractical to carry or handle on most ships. Alternative strategies, like using the engine or steaming around, may be much more sensible.

Ah! Maybe they haven't heard of these so called "New Generation" anchors.

 

[vyv_cox]

Not necessarily. As others have pointed out, the anchors for big things which have to ride out bad weather are colossal, and quite impractical to carry or handle on most ships. Alternative strategies, like using the engine or steaming around, may be much more sensible.

The windage of an aircraft carrier that would have one or maybe two anchors deployed is enormous by comparison with a semi-sub that might have eight of these very large anchors.

 

[JumbleDuck]

Ah! Maybe they haven't heard of these so called "New Generation" anchors.

Still big (nobody ever goes down in weight when they go NG) and even less practical to handle than a Stokes' Pattern.

 

[capnsensible]

On the subject of Merchant Vessels, try a look at Marinetraffic. MV's spend a great deal of time at anchor, waiting to enter harbour, waiting for orders etc often in the worst weather. Some years ago it came up on here that a big storm was heading for the western Approaches and the discussion was about all the ships that dropped the hook east of the Cherbourg Peninsular.

Personally Im quite familiar with the anchorages either side of Gib. The bay for bunkers. These vessels routinely anchor in a hundred metres or more. Twice Ive known ships drag in storms but its rare. Also for interest look at entrance to Suez and Panama canals, the bunker area east of Malta etc or just about any harbour outside the Channel for vessels at anchor.

Of course the RN know how to anchor even if with modern warships its not as routine as it used to be. Actually submarines are fitted with anchors and waaay back it was one of my jobs to operate the windlass if necessary but it was always ready to let go when entering and leaving harbour in case there was a propulsion failure.

So there you go, anchor watching made easy.

 

[Fr J Hackett]

I was sailing of the coast of Anglesey during May 26 1993 whilst the Battle of the Atlantic fleet review was anchored of the coast. There were some fairly strong winds and several warships dragged anchor with some as is the norm in those circumstances contributing to the woes and downfall of others.

 

[noelex]

Generally my experience fits in with the comments from others. Large ships are less secure at anchor than we are.

Here is picture of a large ship sharing an anchorage with us in 50 knots of wind. The white mist is not fog but spray formed when the tops of the waves are blown off.

 

[capnsensible]

. Large ships are less secure at anchor than we are.

You will never, in a million years, convince me that is true!

 

[vyv_cox]

I was sailing of the coast of Anglesey during May 26 1993 whilst the Battle of the Atlantic fleet review was anchored of the coast. There were some fairly strong winds and several warships dragged anchor with some as is the norm in those circumstances contributing to the woes and downfall of others.

I remember that day, reputed to be NE F10. Several smaller warships dragged and had to head for shelter elsewhere. I remember seeing Prince Philip on TV on the deck of a destroyer, having difficulty standing as the wind was so strong.

 

[Fr J Hackett]

I remember that day, reputed to be NE F10. Several smaller warships dragged and had to head for shelter elsewhere. I remember seeing Prince Philip on TV on the deck of a destroyer, having difficulty standing as the wind was so strong.

I was in a small Jeanneau giving the new owner some instruction When it got a bit blowy late afternoon we retired to the straits and tied up inside ( mistake) of Prince Madoc. The storm and lightning were quite spectacular we watched a boat on a mooring gradually lose its genoa as it unfurled, no chance of getting on board. We spent the night on board in relative comfort sheltered by the Prince but effectively trapped by it as the gangway bared exit forward and we had no chance of reversing out. Sunday morning dawned and the owner a good friend sat in the stern with a small cigar in contemplative mood, perfect hamlet moment and asked how we were going to get out and back to Dinorwic. I jokingly said we could cut the rigging drop the mast and motor out under the gangway, without a word he disappeared below and came back with and enormous pair of bolt cutters, he owned a tool store. I told him they wouldn't be needed and we should go ashore in two's, their were four of us and we would see what the day brought. So off two of them went came back suitably refreshed and I and the other crew took our turn. We were just finishing breakfast when a breathless skipper appeared saying something like the wind has dropped. I got up expecting it to have eased but it was dead calm not a breath. We hotfooted it back to the boat and reversed out motored down to Dinorwic locked in just in time for the wind to pipe up again.
Not the only story with that boat and the wind, we broached, blew the kite out and bent the pole and then lost the rudder all before the bar in a round the island (Anglsey) race.

 

[lw395]

Similar came up in a thread ages ago and some links were posted, from memory big ships can't realistically carry the same size anchors as us compared to the size of the boat. So they expect to drag and run the engine in big winds, plus the chain drag on the seabed does help unlike us where it isn't on the seabed when the wind pipes up.

Ships generally anchor where they are out of the main ocean swell. Due to their size, they are not heaved around by shorter waves the way we are. Hence their anchors are working in a much more steady -state condition.
I've sailed through lots of anchored ships off St Helens in a hatful of wind, they were perfectly happy, no way could we have sat at anchor, it was short steep chop.
When your hull is several waves long, it changes the whole game.

 

[capnsensible]

Ships generally anchor where they are out of the main ocean swell.

Fair comment I reckon around Uk waters. But there are an awful lot of very exposed Roadsteads all over the world that routinely get used by thousands of ships a year, some more or less continuously and it takes a fair old storm for them to leave.

I mentioned ^ that there are a lot of vessels anchored at any one time. Try on vesselfinder, for example, Casablanca Roads, or a couple of harbours on that coast. I mention that because I sailed through it a couple of weeks ago and one or two lightly loaded box ships were giving a right old rock and roll. Mebbe one of the Merchant guys who visit here can illuminate the thread a bit further?

Must be a challenge sometimes at anchor holding on to yer coffee on the bridge of one of those ships.......

 

[JumbleDuck]

On the subject of Merchant Vessels, try a look at Marinetraffic. MV's spend a great deal of time at anchor, waiting to enter harbour, waiting for orders etc often in the worst weather. Some years ago it came up on here that a big storm was heading for the western Approaches and the discussion was about all the ships that dropped the hook east of the Cherbourg Peninsular.

By happy coincidence I have a screenshot of that on my laptop - I use it as part of a talk about self-organising systems and crystal structures. So here you are:

 

[Neeves]

Lateral thinking at its best - what a clever analogy.

 

[bbg]

You will never, in a million years, convince me that is true!

Sounds like you need a Spade.

 

[capnsensible]

By happy coincidence I have a screenshot of that on my laptop - I use it as part of a talk about self-organising systems and crystal structures. So here you are:

]

Thats great! Self organising structures doesnt feature much for me but wow, what an effect from that screenshot.