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Maximum anchor chain forces

LOCOPIAS Maximum allowable anchor chain forces

Diagram indicating the maximum allowable anchor chain forces during anchor-handling, according NMD 2007

In June 2007 the Norwegian Maritime Directorate (NMD) released the Guidelines for immediate measures on supply ships and tugs that are used for anchor handling, where additional stability criteria for vessels engaged in anchor-handling are presented. Under effect of the anchor chain force, the heeling angle is limited to:
  • The angle equivalent to a GZ-value equal to 50 % of GZ-max.
  • That which results in water aft on working deck when the deck is calculated as flat.
  • 15 degrees.

Where the heeling moment must be calculated as the total effect of the horizontal and vertical transverse components of force in the wire or the chain.

In order to assess the compliance of a particular loading with these criteria, for each loading condition a polar diagram can be plotted, as an extension to the

 calculation of intact stability, which contains the maximum allowable anchor chain force, as function of the anchor chain angle.