Anchoring big ships

[Kukri]

Umm.

The containership “CSL Virginia” had anchored for thirteen days in this quiet spot off Corsica in October 2018 when the Tunisian ferry “Ulysse” didn’t spot her...

The ferry’s Mate was alone on the bridge and had seen the boxboat on radar, an hour earlier, but he assumed that she was under way and would pass ahead of him. He then stepped into the chart space to write up the deck log, and having done that he sat down in the bridge chair. And we suspect that he then fell asleep..,

 

[Wansworth]

Sometimes on a small coaster there was a need to turn round in a river and dock facing the tide this meant dropping the appropriate anchour on the bottom sufficiently to hold the ships head up and as it swung facing the tide heave it up and make ready to moor up shore side,very busy time on the foredeck at night...........in some ships it was nesessary to stow the chain by hand to prevent it forming a pile,very dangerous as each link weighed a good few pounds.On one old tore out we anchored with the least chain possible as it was never sure that the lister diesel on the anchour windlass would start and on several occasions we missed getting into harbour being unable to get the chain in!On one dark windy night anchored off Yarmouth,Iow we got the anchours crossed over as we had dropped both,the skipper left the wheelhouse to see what was taking so much time,in the mean time the tide got the ship and the mate had to race to the wheelhouse to give full ahead as we drove towards a Russian ship,the anchours had dragged but remained firmly crossed....

 

[PilotWolf]

I think I posted this before, when I was on the Amalfi Coast the ferries used to charge towards the dock and drop an anchor, swing on it and end up perfectly placed stern to. I often wondered what happened if it didn’t hold!

W.

 

[savageseadog]

The most common use of anchoring by commercial ships in the UK that I've seen is in Liverpool Bay near the Bar buoy and also to the East of Anglesey at Moelfre, there's regular traffic there.

 

[SimonFa]

One difference is that they'll have an anchor watch on the bridge at all times, so they won't drag into danger with everyone asleep or ashore. I get the impression that a bit of dragging in strong conditions is therefore expected or tolerated more than in yachts.

Pete

The cruise liners in Weymouth Bay always leave when a south westerly gets up so they obviously don't trust their anchors. Last time my wife checked they go off to the anchorage east of Cherbourg mentioned upthread.

There was only 1 or 2 left there today Usually 6 to 8) and I expect they'll head off overnight as the wind picks up.

The COVID cruise ships in Weymouth bay at first kept floating/cruising around the bay and not anchoring - were they avoiding charges?

They are now anchored, so who gets the money ?

I've never been able to figure out how far out the Portland harbour's remit goes. The cruise liners are managed by Portland radio when they come in and out, but are usually left to their own devices on exactly where they anchor and how close they get to each other from what I've heard on the radio. So if they are in the harbourmaster's area I presume that's where the money goes.

 

[Richard10002]

They definitely do not use power astern to set the anchor - there would be a good chance of something breaking then.

@Kukri can provide a lot more useful info on this topic.

My memory of anchoring big ships is almost 40 years old, so hazy.

However, I do recall that the anchor would be dropped, and the ship would reverse to lay the chain. Then the chain would be secured at so many "shackles", (?), and the officer on the bow would report when it had become taught, then slack. At this point it was considered dug in and holding.

I don't recall whether the power astern was setting the anchor, as well as laying the chain, but the weight of the ship definitely gave the anchor a good tug and, if it hadn't been set, the ship would have continued going backward.

 

[PilotWolf]

I don’t have anyway if posting a picture but if you can see a chart of the Long Beach harbour in California there are maybe several dozen anchorages on the chart inside the breakwater and outside.

All usually assigned by VTS and requirements to call before dropping or heaving anchor. They often will correct a ships position on vhf before dropping.

Rare the weather gets that bad here though.

My biggest concern that that we were never required to have an anchor rigged and ready to use on a 500 t vessel that was only going to want it in an emergency.

W.

 

[Never Grumble]

In the RN, amount of chain cable is calculated using the formula 2x sq root depth. This gives the number of shackles (lengths of chain which are 30 yards/27.5m long) to lay out. An RN vessel will construct a run up plan to that anchorage with marks along the way to measure distance to go aligned with pre-determined engine steps. Most modern ships (with expensive bow domes full of sonar) will approach and drop (or lower if deeper than 27m) in the intended position. They then sternboard away from the drop point laying out the chain in the same manner as a yacht, including snubbing. T23 use a bridle attached to the chain and lowered from the bullring rather then chain hawse to keep the chain away from the bow dome.

A swing circle is then calculated based on the actual position of the anchor at the drop, plus the ship length, plus cable deployed, plus 200m (generally). This is then plotted on the electronic chart and monitored/ship fixed throughout the period at anchor at intervals depending upon the prevailing weather. Engines and steering gear are generally at short notice (shorter notice in worse weather).

26 years since I stood there calling out the distance to run, we never had anything electronic so no one apart from us could check if we were dead in the centre of an anchorage, a cocked hat ensured we always were. I binned all my navigators notebooks so have no recollection of the formula applied. But I do recall that we would apply a brief bit of astern on dropping the pick. Never had to worry about a bow dome.

 

[noelex]

Scale factors mean that anchoring large ships is fundamentally different to our sized vessels.

We only occasionally share anchorages with large ships, but surprisingly they seem to drag more frequently in severe conditions, although in moderate conditions they are typically very secure.

Here is picture of a large ship sharing an anchorage with us in 50k of wind:

 

[newtothis]

Scale factors mean that anchoring large ships is fundamentally different to our sized vessels.

We only occasionally share anchorages with large ships, but surprisingly they seem to drag more frequently in severe conditions, although in moderate conditions they are typically very secure.

Here is picture of a large ship sharing an anchorage with us in 50k of wind:

Typical... no anchor lights or balls.

 

[[2574]]

Thanks all, it’s been interesting. I had no idea that a “shackle” was a unit of length. I’ll be sure to anchor two shackles off the shore next summer.

 

[Neeves]

Off Newcastle, Oz, the coal ships are ordered off the anchorage when winds are expected to increase beyond, I think its 25 knots. After the last one ran aground, having dragged its anchor they are not taking any more chances.

The Captain we know of a cruise ship was motoring against the prevailing winds, Sydney to Freemantle with a full compliment of guests, 2,000, in The Bight when 11m seas were forecast off Cape Leuwin. He anchored to sit it out at Esperance. They set up a rectangle in which to 'keep' the vessel. They deployed the anchor and as the anchor dragged monitored its progress until they reached the leeward end of the 'box', raised the anchor motored to the windward end, deployed anchor etc. I cannot recall if the motored to keep the load off the anchor but the Captain was concerned that the chain lock was adequate for the conditions (which says little for Classification Societies).

I think most modern ships are now equipped with AC14 anchors, which I understand is current state of the art.

I stand to be corrected but a shackle is a unit of length and is the length of a section of chain. Certainly on larger ships the chain comes in 'shackle' pieces joined by a fancy shackle called (something beginning with 'k'). So as mentioned previously - chain is made up of lengths of chain, a shackle long and they carry 'so many' shackles. This is unlike us where we have one complete length, usually.

Jonathan

A 'kenter' shackle.

 

[capnsensible]

Thanks all, it’s been interesting. I had no idea that a “shackle” was a unit of length. I’ll be sure to anchor two shackles off the shore next summer.

A shackle as a multiple of 90 feet could be used for distance off but is generally associated with depth. You could try 'cable' for its convenient tenth of a nautical mile further subdivided as you need, say, half a cable.

Mind you, in my seafaring days under the oceans, I've heard people announcing a visit to the heads by saying 'I'm off to veer a shackle' so it has multiple tasking.

 

[newtothis]

Mind you, in my seafaring days under the oceans, I've heard people announcing a visit to the heads by saying 'I'm off to veer a shackle' so it has multiple tasking.

I'm no expert at anchoring, but I do make every effort to keep all body parts away from the chain and related equipment. This sounds like a health and safety nightmare.

 

[Neeves]

I'm no expert at anchoring, but I do make every effort to keep all body parts away from the chain and related equipment. This sounds like a health and safety nightmare.

it might depend on the gullibility of the audience and the context in which it is mentioned.

Jonathan

 

[Kukri]

“I’m just off to adjust the ullage” was more my line.

 

[Never Grumble]

“I’m just off to adjust the ullage” was more my line.

One shipmate used to say he was "off to give birth to a naval regulator".

 

[westhinder]

Mind you, in my seafaring days under the oceans, I've heard people announcing a visit to the heads by saying 'I'm off to veer a shackle' so it has multiple tasking.

The heads, wasn’t that originally somewhere at the bow, so close to the anchor?

 

[Biggles Wader]

We used to say "Off to see Mustafa"

 

[[2574]]

All anchoring threads always go down the pan.......