Period of Roll & Synchronous Rolling
Period of roll
The period of roll is the time taken for the ship to roll once completely – say from full starboard heel to full starboard heel again.
Synchronous rolling
Rolling of ships is caused by wave action. The wave period and wave height affect the amplitude of the roll of the ship. When the waves are from abeam, the amplitude of roll is greatest while
pitch is absent. If the ship’s course is gradually
altered, the amplitude of roll would progressively
decrease and the angle of pitch would steadily
increase. When the waves are from ahead or from
astern, the pitch would be greatest while there would be no roll.
When the waves are from abeam, if the period of
the waves and the natural period of roll of the ship coincide, synchronous rolling would occur. The amplitude of roll would gradually increase to very high values and the ship may tend to capsize.
Remedial action :
Immediately alter course to break the synchronism. The aim is to prevent the waves from hitting the vessel from abeam.
