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Gard Guidance Masters

2.14.2.11 VESSEL'S BEHAVIOUR DURING PASSAGE – PARAMETRIC ROLLING

For further details please refer to IMO MSC/Circular 707 Guidance to the master for avoiding dangerous situations in following and quartering seas.

Handling a vessel in extreme conditions is a matter of experience combined with basic knowledge of the laws of physics. The Master should ensure that his/her officers always monitor the behaviour of the vessel in heavy weather. If heavy weather is anticipated, the Master should carefully plan together with his/her officers how to monitor the vessel’s behaviour and what actions may be required bearing in mind the prevailing circumstances.

Heavy weather causing damage to the vessel may not only affect the vessel’s safety but that of the crew, the cargo and, in the case of structural failure, the marine environment. The officers should also be made aware of particular areas where extraordinary high waves may occur.

Continuous observation of changes in trim and/or the vessel’s rolling periods is required to avoid excessive rolling, known as parametric rolling. This is an unstable phenomenon which can quickly generate large angles of roll coupled with significant pitch and yaw motions when the following elements are present

the vessel is in head or near head seas

the natural period of rolling

the wave length is of the order of the vessel length

the wave height exceeds the critical level (the height which will allow the vessel’s natural pitch/roll cycle to harmonise with the period of oncoming waves)

the roll damping is low.

Roll damping is dependent on speed. Bow seas result in lower speeds, thus lower roll damping which results in larger roll motions.

The Master should refer to the Company’s SMS and the underlying procedures when navigating in heavy weather.

2.14.2.11 Vessels behaviour during passage - parametric rolling