MSC Circ 1228 Dangers of quartering sea like Synch/ Parametric rolling, Surf riding/ broaching etc discussed along with the factor that cause this & the solution to avoid the issue.

Below MSC Circ. 1228 discussed in detail:

DANGEROUS PHENOMENA
3.1 Phenomena occurring in following and quartering seas
A ship sailing in following or stern quartering seas encounters the waves with a longer period than in beam, head or bow waves, and principal dangers caused in such situation are as follows:
3.1.1 Surf-riding and broaching-to When a ship is situated on the steep forefront of a high wave in following or quartering sea
conditions, the ship can be accelerated to ride on the wave. This is known as surf-riding. In this situation the so-called broaching-to phenomenon may occur, which endangers the ship to
capsizing as a result of a sudden change of the ship’s heading and unexpected large heeling.
3.1.2 Reduction of intact stability when riding a wave crest amidships When a ship is riding on the wave crest, the intact stability can be decreased substantially
according to changes of the submerged hull form. This stability reduction may become critical for wave lengths within the range of 0.6 L up to 2.3 L, where L is the ship’s length in metres.
Within this range the amount of stability reduction is nearly proportional to the wave height.
This situation is particularly dangerous in following and quartering seas, because the duration of riding on the wave crest, which corresponds to the time interval of reduced stability, becomes longer.
3.2 Synchronous rolling motion Large rolling motions may be excited when the natural rolling period of a ship coincides with the
encounter wave period. In case of navigation in following and quartering seas this may happen
when the transverse stability of the ship is marginal and therefore the natural roll period becomes
longer.
3.3 Parametric roll motions
3.3.1 Parametric roll motions with large and dangerous roll amplitudes in waves are due to the variation of stability between the position on the wave crest and the position in the wave trough.
Parametric rolling may occur in two different situations:
.1 The stability varies with an encounter period TE that is about equal to the roll
period TR of the ship (encounter ratio 1:1). The stability attains a minimum once during each roll period. This situation is characterized by asymmetric rolling,
i.e. the amplitude with the wave crest amidships is much greater than the
amplitude to the other side. Due to the tendency of retarded up-righting from the large amplitude, the roll period TR may adapt to the encounter period to a certain extent, so that this kind of parametric rolling may occur with a wide bandwidth of
encounter periods. In quartering seas a transition to harmonic resonance may
become noticeable.
.2 The stability varies with an encounter period TE that is approximately equal to half
the roll period TR of the ship (encounter ratio 1:0.5). The stability attains a minimum twice during each roll period. In following or quartering seas, where the encounter period becomes larger than the wave period, this may only occurwith very large roll periods TR, indicating a marginal intact stability. The result is
symmetric rolling with large amplitudes, again with the tendency of adapting the
ship response to the period of encounter due to reduction of stability on the wave
crest. Parametric rolling with encounter ratio 1:0.5 may also occur in head and
bow seas.
3.3.2 Other than in following or quartering seas, where the variation of stability is solely
effected by the waves passing along the vessel, the frequently heavy heaving and/or pitching in
head or bow seas may contribute to the magnitude of the stability variation, in particular due to
the periodical immersion and emersion of the flared stern frames and bow flare of modern ships.
This may lead to severe parametric roll motions even with small wave induced stability
variations.
3.3.3 The ship’s pitching and heaving periods usually equals the encounter period with the
waves. How much the pitching motion contributes to the parametric roll motion depends on the
timing (coupling) between the pitching and rolling motion.

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