Containers overboard

[LittleSister]

If the speed of the wave and the speed of the ship are such that the roll imparted by the wave passing under the ship has the same period as the ship’s own roll period the wave will amplify the roll and may do so quite dramatically.

How come swells always seem to have the same period as the roll period of whichever vessel I happen to be in?

 

[LittleSister]

Now, let us assume that the ship is under way and there is a long swell. Let’s further assume that the swell is coming from the port quarter. The swell picks up the port side of the counter, passes under the ship’s flat barge shaped mid body, and picks up the flare of the starboard bow. This makes the ship roll. The speed of the swell will be faster than the speed of the ship. If the speed of the wave and the speed of the ship are such that the roll imparted by the wave passing under the ship has the same period as the ship’s own roll period the wave will amplify the roll and may do so quite dramatically.

But presumably can (usually?) be at least mitigated by changing the heading and/or speed of the ship? The period of swells doesn't (usually?) change fast, so could the fact the rolling reached this excessive level be (to some extent?) down to a failure to do so promptly as the rolling built up?

I can't help thinking that, while the ship was rolling badly enough to throw all those containers off, it must have been hellish up on the bridge.

 

[Kukri]

But presumably can (usually?) be at least mitigated by changing the heading and/or speed of the ship? The period of swells doesn't (usually?) change fast, so could the fact the rolling reached this excessive level be (to some extent?) down to a failure to do so promptly as the rolling built up?

I can't help thinking that, while the ship was rolling badly enough to throw all those containers off, it must have been hellish up on the bridge.

Yes. Change the heading or the speed and the roll goes away.

The software promoted by various Class Societies as a solution to the problem simply tries to identify when a sea on the quarter or on the bow is likely to occur with a period of encounter similar to the ship’s roll period and recommends a course alteration.

But the problem doesn’t occur until the roll period imparted by the wave harmonises exactly with the ship’s roll period for that cargo condition. This can happen very suddenly. One minute you are fine… and a few seconds later you are picking yourself off the bulkhead.

 

[Daydream believer]

This guesstimate is built on two boxes in five being empty, one box in twenty being a reefer, one in a hundred being a tanktainer, and maybe one in ten containing stuff in expanded polystyrene .

2 boxes in 5 being empty sounds an awful waste of energy. But of course the container has to return to place of origin to be refilled. It just demonstrates how one sided the trade balance is if things- even raw material- cannot be sent back in return

Reefers- what are they? - Are they the ones full of the things people are supposed to smoke or shove up their noses, or whatever they do with them. If so that is still a hell of a lot coming into the country of destination.

 

[Chiara’s slave]

The 3k was an annualised average figure for 2020-2021. But that was affected by two major incidents in the winter of 20/21, including One Apus, which lost c.1900 and Maersk Essen, which lost 750.
The average over 14 years - the length of time people have been counting - is 1,600, and even that is boosted by the total loss of MOL Comfort, which had 4,200 on board.
I wouldn't worry too much about UK waters as these events tend to take place in the Pacific or Indian oceans, although Maersk did lose a bunch in Biscay a few years back.

Obviously the average includes the large scale catastrophes, they happen. We can’t assume that there won’t be another, so that average is likely to continue. As to the total number of floaters in circulation, you need to consider how long thry float for, as well as what proportion float after they fall in. I have no knowledge of that, but have actually seen a container in the sea, about 25 years ago, in the south atlantic.

 

[mjcoon]

Reefers- what are they? - Are they the ones full of the things people are supposed to smoke or shove up their noses, or whatever they do with them. If so that is still a hell of a lot coming into the country of destination.

Perhaps those are ones that become artificial reefs with wildlife growing or sheltering on them...

 

[Blueboatman]

Perhaps those are ones that become artificial reefs with wildlife growing or sheltering on them...

Nothing that a forward facing metal detector won’t sort out

 

[Supertramp]

In particle physics (IIRC from 50+ years ago) there is a concept of a nucleus cross-section within which a travelling sub-atomic particle may intercept the nucleus. With extreme exaggeration the unit is called the "barn". wikipedia/Barn_(unit)

There must be a similar cross-section in the sea that a yacht may collide with a floating object. This will be of the order of 10m wide or less. So to sail through 120,000 sq km of sea you would have to have a track of 12,000,000 miles I think - but please check!

I think (and hope) you are out by a factor of 1000 or so - a sq km is 10000 10m squares. If not, one in every12m yachts would hit a container after each had sailed a mile.

Is there a risk of significant shoaling from accumulated containers around hotspots?

I'd love to hear the conversation when a Maersk captain calls back to base to tell them he's altering course because it's got a bit rolly on the bridge!!

 

[newtothis]

2 boxes in 5 being empty sounds an awful waste of energy. But of course the container has to return to place of origin to be refilled. It just demonstrates how one sided the trade balance is if things- even raw material- cannot be sent back in return

Reefers- what are they? - Are they the ones full of the things people are supposed to smoke or shove up their noses, or whatever they do with them. If so that is still a hell of a lot coming into the country of destination.

Repositioning empties is one of the biggest logistical headaches for the whole industry. If you look at the Asia-Europe trade, we buy a shitload of shit from China, but export only a bit of whisky and waste paper back. But the Chinese are quite rightly less keen on our waste these days. But that leaves carriers needing to get boxes back to China to fill with more tat. An empty box is a box with no revenue, but still needs to get back.
During the pandemic, as ports got congested, it became harder to dig empties out of stacks, leading to shortages in export markets, leading to some of the crazy high freight rates seen.
Reefers (refrigerated containers) care just insulated boxes with a fridge attached, used mainly for foodstuffs and medicines. The backhaul for these is even worse, as we get lots of food etc from the global south and send little back.

 

[newtothis]

Obviously the average includes the large scale catastrophes, they happen. We can’t assume that there won’t be another, so that average is likely to continue. As to the total number of floaters in circulation, you need to consider how long thry float for, as well as what proportion float after they fall in. I have no knowledge of that, but have actually seen a container in the sea, about 25 years ago, in the south atlantic.

On the whole shipping is getting safer over time so there are fewer. The trend line had been falling between 2013-2019. There's not been a total loss of a large boxship since 2013.

 

[Kukri]

2 boxes in 5 being empty sounds an awful waste of energy. But of course the container has to return to place of origin to be refilled. It just demonstrates how one sided the trade balance is if things- even raw material- cannot be sent back in return

Reefers- what are they? - Are they the ones full of the things people are supposed to smoke or shove up their noses, or whatever they do with them. If so that is still a hell of a lot coming into the country of destination.

Sorry, lapsed into jargon there. “Reefer” = refrigerated (ship or container).

The main trade lanes have become far more “one way” than they used to be. Forty years ago the process of the main trades becoming unbalanced was starting to become apparent. In recent years nine out of ten boxes leave Felixstowe empty.

(edited) - cross posted with Newtothis

 

[capnsensible]

Appreciate the comments from you guys in the business, really promotes understanding,ta.

 

[Bilgediver]

“ so, we was sailing along, yeah ? And then there was this almighty bang .

You were lucky. Some years ago a Contessa 32 with two persons on board from our marina sank between UK and Norway and is believed to have hit a container at night, The boat sank quickly and a life was lost.

 

[Bilgediver]

But the problem doesn’t occur until the roll period imparted by the wave harmonises exactly with the ship’s roll period for that cargo condition. This can happen very suddenly. One minute you are fine… and a few seconds later you are picking yourself off the bulkhead.

It can happen very quickly when it does. I had an experience on a cargo liner some years ago. We were crossing the Pacific heading into the usual lazy swell and travelling at about 18 knots. A tad fast for us Reardon Smith folk bu we were aboard an ex Johnson Line Cargo liner on the Japan Mexico run. Something required attantion up forward and so a descision was made to make a coures alteration to reduce the mount of water spilling onto the deck. I was in my cabin unaware of this. The first I knew was quite suddenly the ship started to roll and each roll a greater amount than the previous and rapidly building up. My concern was for the front windows on the superstructure in the even we rolled so far a wave impacted them.

I was sitting at a long fore and aft table and trapped between it and a bulkhead as I tried to get to the phone to get the engineers to reduce speed. Fortunately they had the same idea and dropped the revs from about 110 down to 50. The effect was immediate. and the haronics were now out of sync and the motion stopped.
We had gone from a zero roll to rolling through at least a 90 deg arc in 3 or 4 cycles. that is quick when you consider the ship had a period of about 16 seconds.

 

[Kukri]

It can happen very quickly when it does. I had an experience on a cargo liner some years ago. We were crossing the Pacific heading into the usual lazy swell and travelling at about 18 knots. A tad fast for us Reardon Smith folk bu we were aboard an ex Johnson Line Cargo liner on the Japan Mexico run. Something required attantion up forward and so a descision was made to make a coures alteration to reduce the mount of water spilling onto the deck. I was in my cabin unaware of this. The first I knew was quite suddenly the ship started to roll and each roll a greater amount than the previous and rapidly building up. My concern was for the front windows on the superstructure in the even we rolled so far a wave impacted them.

I was sitting at a long fore and aft table and trapped between it and a bulkhead as I tried to get to the phone to get the engineers to reduce speed. Fortunately they had the same idea and dropped the revs from about 110 down to 50. The effect was immediate. and the haronics were now out of sync and the motion stopped.
We had gone from a zero roll to rolling through at least a 90 deg arc in 3 or 4 cycles. that is quick when you consider the ship had a period of about 16 seconds.

Perfect example! Thanks for posting this.

 

[Kukri]

This is an example of the other thing mentioned in the Splash247 report - synchronous rolling - the loss of 270 containers from the “MSC Zoe”.

Cargo ship's lost containers bring windfall to Dutch islanders

 

[newtothis]

This is an example of the other thing mentioned in the Splash247 report - synchronous rolling - the loss of 270 containers from the “MSC Zoe”.

Cargo ship's lost containers bring windfall to Dutch islanders

I read the Dutch safety board report into that one. It was more to do with short, steep waves in a shallow waterway hitting the high freeboard beam on, rather than quartering seas causing parametric rolling.
The main recommendations were: don't sail through Wadden Islands in a storm, and get better lashings.

 

[newtothis]

It can happen very quickly when it does. I had an experience on a cargo liner some years ago. We were crossing the Pacific heading into the usual lazy swell and travelling at about 18 knots. A tad fast for us Reardon Smith folk bu we were aboard an ex Johnson Line Cargo liner on the Japan Mexico run. Something required attantion up forward and so a descision was made to make a coures alteration to reduce the mount of water spilling onto the deck. I was in my cabin unaware of this. The first I knew was quite suddenly the ship started to roll and each roll a greater amount than the previous and rapidly building up. My concern was for the front windows on the superstructure in the even we rolled so far a wave impacted them.

I was sitting at a long fore and aft table and trapped between it and a bulkhead as I tried to get to the phone to get the engineers to reduce speed. Fortunately they had the same idea and dropped the revs from about 110 down to 50. The effect was immediate. and the haronics were now out of sync and the motion stopped.
We had gone from a zero roll to rolling through at least a 90 deg arc in 3 or 4 cycles. that is quick when you consider the ship had a period of about 16 seconds.

I've read in some of the scientific reports on parametric rolling that speeding up can also reduce the roll. I think it is to do with breaking the synchronisation with the wave train.
Stories like this make you realise how different it is when a big ship gets heeled over, compared to a small yacht getting a bit tippy.

 

[Kukri]

I read the Dutch safety board report into that one. It was more to do with short, steep waves in a shallow waterway hitting the high freeboard beam on, rather than quartering seas causing parametric rolling.
The main recommendations were: don't sail through Wadden Islands in a storm, and get better lashings.

Yes: Beam seas in shallow water: synchronous roll. The recommended route for large ships in heavy weather has now been moved further away from the coast. Mind you, this patch of the North Sea has been a notorious “graveyard” for centuries.

 

[Bilgediver]

I've read in some of the scientific reports on parametric rolling that speeding up can also reduce the roll. I think it is to do with breaking the synchronisation with the wave train.
Stories like this make you realise how different it is when a big ship gets heeled over, compared to a small yacht getting a bit tippy.

Speeding up would work if you had more speed available. We were ar the designed service speed so only option was to slow down or alter course. The latter might have taken longer. I was surprised how quickly the speed change dampened down the rolling. We left the vessel at reduced speed while attending to the problem up forward and then came back on course and returned to service speed once heading into the swell.