Richard North, 27/03/2021  
 


With the latest discussions on the comments, we're more or less up to speed on the "Ever Given" saga. One thing we haven't discussed is the recent report, expanded here is the report of localised flooding in the bow region.

For the moment, the flooding seems to be confined to the forward void space of the vessel and the bow thruster room. Although, it is not considered to be a major issue, it is considered sufficiently serious for arrangements to be made for high-capacity pumps to reduce the water levels.

This is an added complication in an already complex situation, where the problems are far more serious than the simplistic explainers make it out to be. Not least of the issues is the reference to the high-capacity "suction dredger" which has been deployed. We are told it is being used to remove what is termed the "sand and mud" from under the vessel, at a notional rate of 2,000 cubic meters (sic) every hour.

However, multiple sources, including this one, indicate that the subsoil in the locality where the ship is stuck consists of "nothing but clay" all the way to a depth of 16 metres, "more or less compact" (described as "stiff clay" in some accounts). Unlike the northern end of the canal which was constructed by dredging, the southern end (below the Bitter Lakes) required mechanical excavation.

From observation of photographs and videos, it seems that the bulbous bow of the Ever Given is fairly well embedded deep in the bank, with as much as 15 metres of the bow section grounded. If, below the surface layer of sand and silt, there is clay, the material would not be amenable to dredging. Furthermore, the area underneath the bow, on which it is resting, might not even be accessible to a dredger.

However, from diverse reports, we learn that more powerful tugs are on their way and will be on station by Sunday. With these, another attempt will be made to extricate the vessel, after a further attempt late on Friday failed. This will possibly be on Sunday, or it might be the following day, when tides will be at their highest.

Necessarily, there will be a limit to the amount of force that can be exerted without causing structural damage. This cannot be a straight tow, where the ship can be pulled clear along the axis of entry, and a side pull could create a bending moment for which the ship is not designed.

Presumably, the salvagers have calculated that the hull can tolerate more force than has already been applied - hence the heavier tugs en route. But there will be a limit, and one can imagine that the hull will be wired with multiple stress sensors, the monitoring of which will guide the salvage process.

In order to minimise the bending moment, in what is now being called "Operation Backtwist", it seems that a specific technique is to be adopted. On one side of the ship, a tug will be positioned aft, set to pull the stranded vessel's stern away from the bank, towards mid-channel.

Simultaneously, on the other side of the ship, another tug stationed for'ard, will pull sideways on the bow, inducing the ship to pivot around its centre of mass. Basically, the bulbous bow would be slid off the bank sideways, rather than pulled clear along the axis of entry. This could explain why so much effort is being devoted to dredging the area to the port of the ship (pictured).

In the nature of clay, though, the suction, or "grab" is likely to be very high, creating considerable lateral stresses on the bow section. If, on the day, these are deemed unacceptable, one can see extraction attempts being abandoned. Then the focus will then move to lightening the load. Those on the spot suggest that this could last weeks.

The BBC shows a shore-based crane being used to unload the ship, but it is unlikely that this would be adopted. Crucially, to avoid potentially catastrophic differential stresses, the centre section would have to be lightened first. Shore-based equipment would have insufficient reach.

Inevitably, therefore, a crane-ship will be required although, for the sake of speed several might be needed. The difficulty here will be in finding cranes which have both reach and height, potentially having to extend to 200 feet or so, at a working height of about the same.

Although by heavy lift standards, the weights to be handled will be relatively modest – around 30 tons for a container – the height and reach requirements create their own special problems. Furthermore, given that several thousand containers may have to be lifted, speed of operation will be a vital consideration.

Another factor to take into account is that the Suez Canal is tidal, with the sea running freely from end it end, the flow changing according to season. Tidal range is up to five feet, which is currently being experienced with the spring tides.

With the ship being grounded at both ends, the vertical movement of water is imposing stresses on the centre section of the ship, for which it was simply not designed to take. Constant movement over a period of time can induce micro-cracks which can develop into major fractures, with a risk that the ship breaks apart.

With such solid-looking ships, it hardly seems conceivable that one could break apart, but it has happened before. On 17 June 2013, the 90,000 ton MOL Comfort suffered a crack amidships in bad weather about 200 nautical miles off the coast of Yemen. It eventually broke into two, both parts sinking several days later.

With a length of some 316 metres, and less than half the displacement of the Ever Given, it also carried less than half the load, then 4,382 containers. And while the circumstances of its sinking are clearly very different from the predicament of the Ever Given, the size of this ULCV creates its own particular problems.

As this article suggests, building ships of this size is pushing at the boundaries of technology while the push to build cheap ships, in order to maximise operators' profits, means that they are engineered down to specification rather than to maximise safety.

Structural considerations aside, there are also questions as to whether such large ships can be safely handled in the challenging conditions of the Suez Canal. The article cited points out that the Ever Given has a wind area of roughly 20,000 square metres. The largest Clipper ships, fully rigged, had about 5,000 square metres of sail.

If, as is believed, the Ever Given encountered 30kts of wind on the beam, the resultant force applied would be 270 tons directly against the ship. The average modern harbour tractor tug can produce 70-80 tons of force at full power. A 30kt beam wind, therefore, would be equivalent to having three harbour tractor tugs pushing against the ship at full power.

With the ship attempting to navigate a narrow channel, in poor visibility due to a sand storm, with gusts of up to 40kts at the time of the grounding, this most likely exceeded safety parameters.

Furthermore, this is not the first time the Ever Given has had such problems. On 9 February 2019, the ship struck and heavily damaged a 25-metre-long HADAG ferry boat at Blankenese, near Hamburg. Two minutes after the collision, a traffic ban on the Elbe river was issued due to high winds. The ferry was a total loss.

Such ships entering confined harbour spaces usually have heavy tugs to ensure station-keeping and, in the Panama Canal, ships are towed through lock sections by shore-based locomotives known as "mules", helping steer large ships and preventing them from hitting and damaging the canal banks. Even then, accidents happen.

To ensure maximum safety, heavy tugs and rescue equipment needs to be stationed close to hand, for use in emergency. That equipment in this incident is having to be pulled in from some distance, with the inevitable time lags, tells its own story.

Therefore, finishing, as before, on a political note, much here points to operations being pared down to minimum safety levels in order to contain costs. If that is what is powering Johnson's "Global Britain", then this might turn out to be an object lesson – that resilience comes at a price, one that could undermine the whole basis of his policy.

Also published on Turbulent Times.






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