ABS offers new parametric roll notation

In recent years, a phenomena known as "parametric roll" has gotten a great deal of attention from designers and operators of containerships as well as insurers.

A large unstable rolling that occurs in head or stern seas, parametric roll has been blamed for incidents where stacks of containers have gone overboard or collapsed on deck.

Some postPanamax containerships, with wide beams and flared bows are thought to be particularly vulnerable to parametric roll, and it is more likely when a ship with a particular speed and course encounters a certain sea state under certain load conditions.

Now the American Bureau of Shipping has issued what it believes is the first class notation specific to parametric roll.

The bureau determines if a particular vessel is vulnerable to parametric roll and the potential magnitude of the roll motions. ABS said this is the first criterion created by a class society that addresses the subject that is "firmly based on ship motion analysis supported by extensive simulations."

The "PARR C1" notation has been granted to the 4,700TEU Hyundai Forward, and 8,600TEU vessels Hyundai Faith and Hyundai Force.

Having the notation doesn't mean a containership is less vulnerable to parametric roll, it's more of an "awareness program," explained Jennifer Bewley, an ABS spokesperson. The classification society prepares a manual for the master and provides training on how to deal with the phenomena.

Some ships have a feature designed to help combat parametric rolling called flume tanks, interconnected ballast tanks with baffles that attempt to use ballast water to help combat the rolling on ships.

 
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