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June 8, 2005

New ABS Ice Class Guidance Notes

As demand for ice class tankers continues to grow, ABS has issued a new set of comprehensive Guidance Notes on Ice Class.

The Notes build on ABS's research on nonlinear finite element analysis of side structures subject to ice loads. They provide direct calculation procedures for designing ice strengthened vessels by addressing three principal elements in ice strengthening design that are considered the key factors in determining the ability of a vessel to operate safely in ice infested waters:

  • alternative side structures,
  • minimum propulsion power requirements and
  • strength of the propeller.
  • In 2003 ABS published detailed procedures for evaluating alternative structural designs using nonlinear finite element method (FEM). This was in response to the issuance of interim guidelines from the Finnish Maritime Administration (FMA) regarding direct calculations for longitudinally framed hull structures.

    The just published Notes are an extension of that work and offer alternative methods for the determination of minimum propulsion power requirements and procedures for propeller strength assessment based on FEM, which is a new approach to the analysis applicable to ice class vessels. The Notes include guidance for ice propulsion analysis, with supporting model and full-scale test data, ice load definitions and stress analysis of ship structures due to ice loads.

    These direct calculation methodologies help to identify the more balanced structural arrangements and propeller blade strength criteria to meet the most stringent ice class requirements. The Notes supplement ABS ice class requirements contained within the ABS Steel Vessel Rules.

    Ice thickness and severity create a multitude of technical considerations for the entire hull.

    "Although reinforcement in the bow design is a primary concern, midbody and aft areas must be considered and the form of the hull must handle the ice-strengthened propulsion requirements and the compressive ice pressure should the vessel become trapped," says Akira Akiyama, Vice President, Technology & Business Development, ABS Pacific.

    Akiyama stresses ABS' more than 50-year history of establishing standards for and evaluating designs of all ship types, including ice breakers, to both Baltic Ice Class standards and for worldwide trading in areas subject to ice such as the winter St. Lawrence.

    Most recently ABS has been selected to class several new aframax ice class tankers, ordered at leading Asian shipyards to meet expected future increases in Russian oil shipments through Baltic export terminals.

    Currently 312 ships, including 56 tankers, totaling 5.1 million grt are in worldwide service with ABS ice class notations. An additional 13 new tankers are under construction to ABS Baltic Ice Class standards.

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