There has been, unsurprisingly since the Costa Concordia loss, much talk about the need to improve damaged stability on ships. More subdivision, cross-flooding arrangements and means of providing more pumping capacity are all being discussed. But what about intact stability and its importance in keeping a ship safely upright and afloat? Is this being properly taught and its principles understood by people who operate ships day by day?
It could be that, as in other aspects of ship operation, stability is being taken out of the hands of people who would once work it out longhand, but who now rely entirely on what their computer tells them. But what if the data fed in is deficient, or there is no understanding of the effects of phenomena like, for instance, slack tanks. There have been rather too many cases of ships falling on their sides and surprising everyone and it is too easy to just blame it on the cargo and underestimated weights. Stability really matters.
Should a passenger ship be blown over, as seems to have happened to the Eastern Star, which killed more than 400 people in the recent Yangtse disaster? The vessel was designed with a shallow draught, and never expecting to go to sea, with little freeboard. Like hundreds of other river tourist craft and inland ferries, the ship was in no way exceptional, but seems to have capsized after her lee deck edge submerged in a sudden violent wind.
You cannot stop a floating body listing with external forces, but where was the righting moment that should have brought her upright again? There are plenty of questions to which grieving families require answers, about design, operations, but importantly, the loss of stability which overwhelmed the craft in little more than a few minutes. These are important questions too, thinking of all those hundreds of other passenger ships in so many of the world’s waterways.
Author: Michael Grey Source: claymaitland.com