4.2 How to avoid dangerous conditions
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1228 – Revised Guidance to the Master for Avoiding Dangerous Situations in Adverse Weather and Sea Conditions – (11 January 2007) - Annex - Revised Guidance to the Master for Avoiding Dangerous Situations in Adverse Weather and Sea Conditions - 4 Operational Guidance - 4.2 How to avoid dangerous conditions

4.2 How to avoid dangerous conditions

Parent topic: 4 Operational Guidance

4.2.1 For surf-riding and broaching-to

 Surf-riding and broaching-to may occur when the angle of encounter is in the range 135°<α<225° and the ship speed is higher than . To avoid surf riding, and possible broaching the ship speed, the course or both should be taken outside the dangerous region reported in figure 2.

Risk of surf-riding in following or quartering seas

4.2.2 For successive high-wave attack

  4.2.2.1 When the average wave length is larger than 0.8 L and the significant wave height is larger than 0.04 L, and at the same time some indices of dangerous behaviour of the ship can be clearly seen, the master should pay attention not to enter in the dangerous zone as indicated in figure 3. When the ship is situated in this dangerous zone, the ship speed should be reduced or the ship course should be changed to prevent successive attack of high waves, which could induce the danger due to the reduction of intact stability, synchronous rolling motions, parametric rolling motions or combination of various phenomena.

  4.2.2.2 The dangerous zone indicated in figure 3 corresponds to such conditions for which the encounter wave period (TE) is nearly equal to double (i.e., about 1.8-3.0 times) of the wave period (TW) (according to figure 1 or paragraph 1.4).

4.2.3 For synchronous rolling and parametric rolling motions

  4.2.3.1 The master should prevent a synchronous rolling motion which will occur when the encounter wave period TE is nearly equal to the natural rolling period of ship TR.

  4.2.3.2 For avoiding parametric rolling in following, quartering, head, bow or beam seas the course and speed of the ship should be selected in a way to avoid conditions for which the encounter period is close to the ship roll period or the encounter period is close to one half of the ship roll period .

  4.2.3.3 The period of encounter TE may be determined from figure 1 by entering with the ship's speed in knots, the encounter angle α and the wave period TW.

Risk of successive high wave attack in following and quartering seas
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