MASTER EXAM ORAL QUESTIONS AND ANSWERS - LATEST QUESTIONS | Page 33

282
FOLLOW

When the period of encounter of wave is the same as the roll period of the vessel and when waves are experienced from beam of vessel it is called synchronised rolling.This situation can be avoided by altering course

146
FOLLOW

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. Its more pronounced in beam seas

Parametric rolling
When the rolling period is equal to or twice the wave encounter period. When the crest is in amidship the ship rolls the maximum n also the gm is reduced to minimum. The most dangerous is when the ship pitches twice for every roll.
When the vessel pitches into the crest the buoyancy increases and pushes the ship on to other side causing violent roll, n this coupled with reduced gm when the crest is amidship, can cause the ship to capsize.

Action. Ship speed and course should be reduced in such a way that the above condition is not met.

For ship's loading condition with high GMs, i.e. shorter natural roll period say around 10 second, the waves that could cause the pitching period around 5 seconds are usually not very high and therefore unlikely to initiate parametric rolling in head/stern seas. However, the synchronous roll may occur
in beam seas. So the way to reduce the roll is by heading into the sea.
 
For ship's loading conditions with low GMs, i.e. long natural roll periods, parametric roll in head/stern seas of moderately high sea state is likely. But synchronous roll in beam seas is unlikely. Containers are  more prone for parametric rolling

146
FOLLOW

It provides useful information when drydocking the vessel. It provides measurements needed by the drydock personnel to position the blocks and sidebeds (bilgeshore). Apart from that it provides other information as well, such as docking draught and trim, air draught, hull paint areas, weights aboard to achieve docking trim, grades of steel used in specified areas and position of bottom plugs, echo sounder and log , draught sensors. The docking plan is useful alternative to the GA plan and the capacity plan when measurements are required

21
FOLLOW

The following immediate action should be taken by any ship receiving a distress message:
.. acknowledge receipt of message.(DO NOT SEND A DSC ACKNOWLEDGEMENT) Listen Only.
.. gather the following information from the craft in distress if possible:
- position of distressed craft
- distressed craft's identity, call sign, and name
- number of POBs
- nature of the distress or casualty
- type of assistance required
- number of victims, if any
- distressed craft's course and speed
- type of craft, and cargo carried
- any other pertinent information that might facilitate the rescue
%uDBC0%uDC89 maintain a continuous watch on the following international frequencies, if equipped to do so:
- 500 kHz (radiotelegraphy)
- 2182 kHz (radiotelephone)
- 1 56.8 MHz FM (Channel 16, radiotelephony) for vessel distress
- 121.5 MHz AM (radiotelephony) for aircraft distress
%u2022%u2022 Vessels should maintain communications with the distressed craft while attempting to advise the SAR system of the situation.
%u2022%u2022If it is clear the ship or persons in distress are not in the vicinity and/or other craft are better placed to assist, superfluous communications, which could interfere with SAR activities are to be avoided. Details should be recorded in the appropriate logbooks.
%u2022%u2022Reconsider the decision not to proceed nor report to the SAR service when vessel in distress is far from land or in an area where density of shipping is low.

146
FOLLOW

Surfing
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.
Broaching
Broaching is an unintentional change in the horizontal-plane kinematics of a ship. Broadly, it may be described as the “loss of heading” by an actively steered ship, that is accompanied by an uncontrollable build-up of large deviation from the desired course. Broaching is more The third distinctively identified, commonly arising in waves which come from behind and propagate in a direction forming a small angle, say 10-30deg, with the longitudinal axis of the ship. Although the inception of broaching represents a problem of instability on the horizontal plane, capsize may be incurred at the post critical stage due to development of large heel as energy is transferred into the roll direction. Broaching could happen to small as well as to larger ships. It is notable however that the dynamics involved do not seem to fit always into a single pattern. Frequently, broaching is manifested as a sudden divergent yaw, which peaks within a single wave length. Control is lost when the middle of the ship lies somewhere on the down-slope and nearer to the trough. In other cases there is a gradual, oscillatory-type build-up of yaw as successive waves impinge on the ship from behind. In moderate sea states a ship is more likely to broach-to if it runs with a high speed and is slowly overtaken by the waves. Broaching may also occur at lower speeds if the waves are very steep.

Action :Course and speed to be changed to avoid surf riding and broaching