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Anatomy of an Accident: Why INS Betwa Tipped Over
Brahmaputra-class frigate INS Betwa (R) and stealth frigate INS Shivalik (L) at Chennai port to participate in Exercise Malabar 2015.
Image Credit: Indian Navy photo

Anatomy of an Accident: Why INS Betwa Tipped Over

 
 

India’s maritime woes are manifesting in multiple ways. In an unprecedented accident earlier this week, an Indian naval warship, the INS Betwa, slipped off her dock-blocks in a ship repair facility in Mumbai, suffering extensive damage. A Brahmaputra-class guided missile warship, the Betwa was in the process of undocking when the unfortunate incident occurred, killing two sailors and injuring another 15.

It is crushingly embarrassing for the navy and the Western Naval Command to face the ignominy of a 4,000-ton warship turning turtle in a dry dock. The fact that the mishap is only the latest in a long list of serious accidents involving Indian naval ships and submarines is an unsettling truth that naval commanders are finding hard to come to terms with.

As expected, an official inquiry is underway, but given the ship’s size and nature of the accident, it may be several weeks, perhaps even months, before the report is rendered, identifying causes and fixing responsibility. There are many aspects that the board will need to consider. Officials will have to closely examine the undocking plan and ascertain the exact sequence of events leading up to the accident. There are important questions surrounding the distribution of weight on the ship, positioning of personnel on board for necessary checks, and the possibility of a violation of procedures. In the main, the inquest will focus on identifying particular lapses that led to the failure of the hull support mechanism, and whether there was an infringement or subversion of prescribed protocols.

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Given the foggy nature of the information at hand, any post-accident analysis would seem highly premature. However, even at the risk of faulty diagnosis, it may still be worthwhile to consider likely possibilities of where things may have gone wrong.

A ship’s undocking is a delicate process and always carried out in a carefully controlled environment. The essential principle followed is simple: allow water to fill the dock in calibrated fashion to allow the ship placed on dock blocks to float itself, without too much external intervention. Weight calculations are scrupulously done, and ballast conditions properly ensured to let the process take place gradually and organically.

Rarely does an undocking procedure dramatically unravel, unless one of the following three conditions occurs. If the dock blocks are improperly assembled or even in poor material condition, they could — in theory — give way, especially at the time when ship’s hull is just beginning to float, causing it to shift on the blocks. Such a possibility, however, is improbable because dock managers and engineers are known to be scrupulous about the quality and assemblage of dock blocks, as well as other supporting infrastructure that supports the ship’s hull during dock-repairs.

The more likely scenario is that the weight calculations were slightly — even if not substantially — off the mark; not enough to be alarming, but sufficient to cause a slight weight imbalance as the ship began lifting off the blocks. As opposed to cargo vessels that have a U-shaped hull, warships have a V-shaped bottom that makes trim (difference between the draft forward and aft) a critical requirement. It is important during the undocking of a ship for the front portion to lift first before letting the aft section float. If the reverse happens, there is likely to be excessive stress on the blocks holding the hull.

Speaking to the media after the incident, Defense Minister Manohar Parrikar said that a weight imbalance may have been the reason behind the accident. When a ship undergoes refit, he stated, a lot of machinery is removed; as a result, the balance gets disturbed. The resultant shift in the center of gravity, he suggested, could have caused the accident. The Betwa, however, is not the first ship in refit to have its internal machinery removed. It happens every time a ship is docked for an extended duration refit. Even so, a strict account is kept of the weight and placement of equipment removed and relocated, and also of the resulting load displacement; every time a ship is undocked, personnel involved in the operation have a clear idea of actions needed to keep the vessel on even keel.

There is also a third possibility that the port (left) side of the ship was somehow heavier than the starboard (right), causing the ship to become imbalanced and topple over. This again is an unusual occurrence because weight calculations are made well in advance and correct load distribution certified before the undocking procedure gets underway.

Interestingly, while the captain of the ship is responsible for its safety in harbor and at sea, the dock master assumes responsibility when the ship enters a dry dock. It rests on the latter to orchestrate a safe dry docking and undocking operation, for which he has a trained crew and specialized dry dock equipment. He is mainly responsible for planning, coordination and execution of the entire operation.

This is not to suggest that the ship’s crew is free of all responsibility. Experts say that in a freak one-off, a sea-inlet valve on the port side may not been improperly secured by personnel on board, resulting in the ingress of water during the dock’s flooding, causing a weight imbalance. But this seems unlikely because bottom compartments are always being inspected for leakages during an undocking.

Maybe things got complicated when the water leaking into the ship was noticed after the bottom had been set afloat. This would have required the rear end to be settled back on the block by pumping out water from the dock. If the hull wasn’t positioned on its keel blocks properly then a loss of meta-centric height could have unbalanced the ship.

For some, there are other explanations. As one ship engineer pointed out after the accident, an important requirement for smooth undocking is consistent alignment – making sure the ship is kept still and pointing in one direction. This is accomplished with the help of heavy ropes that keep the ship aligned to the median line. If the water was filling in too rapidly, or if there were strong wind gusts, experts say, the ship’s forepeak could have laterally shifted away from the center, causing excessive strain on the dock blocks.

One suggestion has it that the timing of the incident – 1:50 p.m. — may have something to do with “lunch hour.” Dockyard workers are known to be finicky about lunch timings and sometimes take up to a two hour break for the afternoon meal. They may have been rushing through the undocking procedure with an eye toward lunch hour, or maybe they returned from late from their meal and were in the middle of the undocking procedure when the realization dawned that the tide had turned unfavorable, resulting in a temporary stall in proceedings. By then, the strain on the blocks, or an imbalance in weight, had taken a toll.

And yet, all explanations on offer are at best informed speculation. At the moment, a “technical evaluation” is underway in naval dockyard Mumbai to assess damage to the ship and set it upright. Apparently, foreign experts are being flown in to offer advice on how to salvage the ship. The Chief of Naval Staff (CNS) Admiral Sunil Lanba has expressed his resolve to get Betwa back on its keel and serviceable in quick time.

That does look like a tall order. How and when it will be accomplished, only time will tell.

Abhijit Singh is a Senior Fellow at the Observer Research Fellow in New Delhi.

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