I agree with Dutchie but the problem is handling heavier lashing rods. It is already pretty dangerous on the outboard stacks with a rod to the third height. There is no easy way I can see of increasing the strength of the present design of twist locks and deck fittings.
So the question has to be “how big is too big”.
Looking at the photos the MSC Zoe was in good condition as one should reasonably expect for a ship that is only four years old. When we consider the same vessel the same age as the APL England we have a problem. The bosun and 4 crew have about 5400 square metres of deck to look after each. That is about 1and 1 third acres each. Time to take some gardening leave.
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The angle of the skewed line in the drawing reflects as good as possible the figures given in the Scientific Analysis. It gives an overview of the acceleration forces versus the roll angle.
From the report:
According to crew statements, at 23.00 hours on the evening of 1 January 2019, the MSC ZOE suddenly started to roll violently which felt like rolling angles of 20° till 30°, for a period of around 30 seconds. These movements were so violent that the equipment in the fitness area shifted and on the bridge various items, including the printer, flew through the air. According to the crew, after this period of violent rolling, the movements of the vessel returned to the previous 5 to 10° roll.
From personal experience I know this phenomenon as once on a tanker, in the middle of the night during stormy weather, I was catapulted out of my berth to the bench on the other side of my cabin. That was my luck, otherwise… All the drawers from underneath my berth also flew through the cabin and that while they had a lock system to prevent it from just doing that. We had a lot of damage on deck, also part of the ‘chicken walk’ as we called it, your cat walk, was swept away. Now we had to walk over the deck to get to the mess room aft.
The cause of the violent motion could be two or more waves that add up algebraically, a very high wave preceded by a deep trough may occur. This may be referred to as an ‘episodic wave’, i.e. a random large wave, noticeably of greater height than its precursors or successors, which occurs when one or more wave trains fall into phase with another so that a wave or waves of large amplitude is/are produced giving rise to sudden steep and violent rolling and/or pitching of the ship. These are popularly, and incorrectly, referred to as ‘freak’ wave.
The 30° roll, which amounts to 7.84 m/sec² or 0.8 g, is doubted by the Scientific Analysis and is indeed a very high value. It is a pity that on such a state of the art ship no trustworthy electronic inclinometer was available. The excessive acceleration criterium R1 (m/sec²) in the formula is the standard for lateral acceleration and the value of standard is defined as R1 = 7.848 m/s2 for ships with the length between perpendiculars greater than 250.0 m. Note that the ship’s value of 7.84 m/sec² is a fraction below the standard.
According to the graph the lashings must hold to at least a roll of 18.74°. That I don’t understand since that figure can be reached in bad weather rather easily…
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I wonder if this is a case of the construction of these ships outpacing the regulations?
I also wonder if the designers figured this all out? Did they calculate that if less then x% of boxes get thrown off in weather that the ship will still be profitable?
Would moving the cost of the damage to the environment from an externality to the bottom line change the equation? Say fine the company a million dollars a box, or whatever it takes…
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I am sure that this is the case. It looks like they scale up to ever larger ships and donot look further. I think that the shore facilities will ultimately dictate where the number of containers on a ship will end.
In the old days the owners, like Nedlloyd, had their own technical departments. The ship designs were based on research of Nedlloyd’s Newbuilding Department on cargo handling, port performance and ”care for cargo” under the inspiring leadership of naval architect Vossnack. In that department was a lot of ship expertise because a number of former captains and other officers were part of it. The ship’s were in fact designed there and the yard had only to translate their plans into official shipbuilding drawings.
Nothing escaped the attention of the old guys. I am afraid that this is all gone these days. Now the shipyard can make shortcuts and nobody will notice because the bean counters, I like that word, who are in charge have no idea what a ship is.
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Maybe, I have a heretic thought:
Were the growing container piles above deck, and even above the ship’s guides, not considering the larger transversal accelerations on the top containers?
Would it not be better to stack the containers transversally on the ship, with more flat lashing angles? Indeed, all gantry cranes, all dockside dispositions and all older or new ships were built for longitudinal transport…
The very steep lashing angles of the longitudinally stocked containers, give a very high vertical compression on the edges of lower containers. The pictures show nearly always the crushing of the lower containers.
The ship’s guides help retain the stack vertically, but cannot interdict the millimeter range movements of the containers, transferring the huge vertical forces downwards. Stiffening the lashings could even augment the vertical forces…
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Makes lots of sense to this WAFI. But designed beam of the vessel would be less flexible.
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Interesting thought! I suppose that it requires some calculations and research of the design changes that are required. Another point is if the shore facility “as is” can handle the containers to be stacked in that manner. If a new line of cranes are necessary, next to the standard cranes, then I think that this will be a financial and operational problem. And not the least it requires a new generation of container ships because I don’t think that the present ones can be adopted in a cost effective way to the new system.
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Same cranes just build a container spreader that has a slewing function. Lift box off ship spin 90 in the air, set down on chassis. Same traffic lanes on land. Do you stack them doors out or in? Would rolling on that axis require stronger bracing / blocking of cargo inside box?
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The Chinese will be happy to supply the cranes needed to implement the change.
Unfortunately most container spreaders on STS cranes look like this:
But a spreader like this could probably be modified to do what you suggest:
Not sure if they can handle various sizes of containers on a single point.
(The CoG of the containers would have to be fairly centered to do that)
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The single point suspension spreader pictured is normally used on slewing crane usually found on general purpose berths. The suspension point automatically adjusts by moving fore and aft as can be seen in the photograph to the COG of the container.
The single point suspension is attached to a spotter motor that keeps the container fore and aft as the load is moved through 90 degrees.
The spotter motor can be controlled by the operator and can handle a container loaded transversely.
Often such a crane is the only option where there has been a major collapse of the stow such as MSC Zoe.
A skilled crane operator can get up to about 22 to 25 MPH but a gantry crane requires less skill to exceed this rate.
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Lessons learnt from the MSC Zoe incident:
https://safety4sea.com/lessons-learned-after-loss-of-containers-from-msc-zoe/?cf_chl_jschl_tk=5594b15b14224d61fa08c94d99f7beb18f02b3e3-1593605114-0-Acf-aYfSwYxGHBmfD3bsH7EtRSYT-wnuZbHPy4eTAypQap3RZmctl9eOJCkgypyGFvb4Ddhkb54zMV_688aRC_vidHQzj3cUDIZtoW4I8pPCDT45oCej5vUWtla4Yzd-751sN71WjXXSHetdePHdrhyBPOuHeq2X7SfTx3QxzTDTSVbXxytJjVBoCG8udGo53wHUJP-6T51UMrmuszSoh2c92QXRvyzoyB5Xk5C_imzw2Xfyfn85LF9sRFL1lz06KILsU5WTgQpP7LQ8qenDLfm3R8U7IaD2lSLRtq9nnUjsMYAldvvf4CzJJt_XU_BZ6Q2MZXOz5tozMUHFx5Jkk0ococNx7ZN2uPb6YQqkWfjl
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What I don’t understand is that why they not just close the shallow water and higher risk southern route that is so close to a vulnerable internationally recognized nature reserve. You can almost spit on the shore from the ships on this route. Undoubtedly other accidents with container loss are bound to happen, it is just a matter of time. And what about oil spills, that could have even far worse effects.
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Even in moderate seas very large vessels can roll to an angle of 10°. In bad weather, angles of 30° are not unusual. Large container ships must be expected to roll to such angles. Stabilizers and other anti-heeling systems may help to damp ship movements. Ship’s speed is directly connected with roll damping, the higher the speed the larger is the roll damping. However, not all systems are usable or sufficiently effective in bad weather. For instance ship’s speed is dependent on the weather circumstances.
On rare occasions, rolling angles may reach 45° and even above in exceptional cases. It is easy to imagine what that means for inadequately secured container cargoes. Overall, containers may be exposed to such accelerations for very long periods of time when at sea. Moreover, the oscillations may be superimposed one on the others like gravity. slamming, vibration from the hull that can be transferred to the cargo. Goods are then exposed to stresses from the extremely low frequency oscillations generated by sea conditions and by higher frequency machinery and propeller vibration.and be intensified.
At a rolling period of 10 sec a ship moves side to side 8640 times daily. Over several days’ bad weather, the cargo will thus be exposed to alternating loads tens of thousands of times. All shipping packages must accordingly be constructed so as to be able to withstand 0.8 times the weight of all adjacently stowed cargo and twice the mass of the cargo loaded on top. If this is not the case, appropriate protective measures must be taken. Additional rigid receptacles, frames, false decks and similar measures may be helpful.
Has Passive Anti-Roll tanks been considered for large Container ships?:
They are common on Offshore vessels, Fishing vessels etc.and works fine in low speed (or no speed)
Some year back I took delivery on behalf of buyers of a Russian Longliner that had gone bankrupt and was under arrest in Pusan, S.Korea.She was built in Norway to Norwegian design:
She had a Passive Anti-Roll tank just below the bridge.
This position was to maximise the effect with a minimum of deadweight loss.
I was mate on a small two hatch, lower tween deck and shelter deck ship built for the coastal trade in Norway with a pallet loader. The flume tanks worked a treat on her as they did on an oceanographic ship I sailed in. We had a large RoRo here on TransTasman trade with stabilisers. She had an engine failure in bad weather and they unloaded about 100 new cars with dustpans and brooms. Some of the deck cargo went over the side.
You may see the longliner Janas when she once in a while pay a visit to her home port of Nelson.
I think passive anti-roll tanks could be arranged even on existing large container ships.
This can be done either by using double bottom and wing tanks, (which will “steal” a lot of dwt to be efficient) or by “stealing” one layer in one row of 20’ containers across at hatch level.
The last would reduce the max TEU capacity by no more that 24 TEUs on a Megaship (>20000 TEU) and could be installed in a few days at a well equipped shipyard.
PS> On the Janas the A/R Tk. had emergency dump valves that could empty it in a few minutes, if necessary.
PPS> A/R tanks and anti-heel tanks are two VERY different things and should NOT be in use simultaneously. (Like when handling cargo) (Or when doing Anchor handling: Refr, Bourbon Dolphin)
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@Urs Your heretic idea, looking at this picture, seems to pay off! The barge lost a number of containers off Hilo, see elsewhere. Notice that the two white containers up front are still standing tall!
Looking at it from a mechanical point of view: moment is force times distance. Much more force is required to break away a transversely stowed container as compared with a longitudinally stowed one. A 40 ft container length is 12.2 m and the height is 2.9 m. Thus 12.2/2.9 = 4.21 times larger than if stowed longitudinally. Ultimately this means that a force of 4.21 times larger is required to break the lashings. I hope my calculation is correct…
Another advantages, when stowing containers transversely, is that pitching angles are much smaller than rolling angles.
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Urs, take a look at the picture (on gCaptain) of the barge in Hawaii that lost containers a few days ago. - they stach containers both ways on that barge, and it looks like the transverse oriented containers were fine while the fore-and-aft ones failed.
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The other thing it indicates is the stacks on the after end seem most vulnerable. Here, because it’s a barge we cannot blame engine vibrations on it. All I can think of is slamming due to the flat run aft to the transom.