ABS issues new ice class guide

25 May 2004

ABS offers comparative structural arrangement studies for the design of each tanker ice class designation using procedures outlined in a just released ?Guide for Non-Linear Finite Element Analysis (FEA) for Side Structures Subject to Ice Loads.?

The guide is an outgrowth from ABS' work with the principal Asian shipyards developing new Aframax ice class tanker designs in response to the increased traffic in the Baltic. Growing oil exports from the Russian port of Primorsk and Sakhalin have prompted a marked increase in the number of new tankers on order with ice strengthening to allow more flexible trading. Additionally, operators are taking into consideration the 2010 IMO imposed single hull phase-out deadline as they renew their Aframax fleets.

"The FEA Guide allows us to perform direct calculations for developing alternative structural arrangements that are more producible than those developed from the prescriptive rules," says Akira Akiyama, Vice President, Technology & Business Development, ABS Pacific.

These direct calculation methodologies help ABS to identify the simplest structural arrangements and optimal horsepower to meet the most stringent ice class requirements. "In the case of machinery output, credit can be given for increasing propeller performance and reducing ice resistance. In the case of the latter, ABS provides guidance on model tests to determine powering requirements," he adds.

"For a typical Aframax tanker the percentage of steel weight increases by as much as 16% for a Finnish Ice Class 1A Super or ABS notation equivalent of 1AA," Akiyama points out. "Both owners and yards are looking to the classification societies to help them meet these requirements in the most cost effective manner without compromising the structural and operational capability of the vessel."

ABS ice class requirements are incorporated into its Steel Vessel Rules. The notations indicate the thickness and severity of the ice conditions for which the vessel has been designed and built.

"Although reinforcement in the bow design is a primary concern, there are technical considerations for the entire hull," says Akiyama. "The midbody and aft areas must be considered and the form of the hull must handle the ice-strengthened propulsion requirements and also handle compressive ice pressure if the vessel becomes trapped."

By analyzing such factors as the period and severity of the expected ice conditions for specified areas of operation, including the presence of multi-year ice, ABS can provide valuable input to an owner's decision making when selecting the most suitable ice class for a newbuilding.

Although there is a lot of attention being paid to the new generation of ice class tankers, the technology is also applicable to many other vessels, from containerships trading year-round into Montreal, to drill barges in the Caspian Sea, to the new generation of LNG carriers and the ABS-classed drilling and production unit in service off Sakhalin.

According to Clarkson Research Studies, there are currently 137 vessels on order with ice strengthening and of these 65 are to be constructed to ice class 1A. The ice class fleet is expected to grow by 9% in 2004, 12% in 2005 and 33% in 2006, predicts Clarkson.

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