Question

Describe the general precaution taken against capsizing

General Precautions against Capsizing

Compliance with the stability criteria does not ensure immunity against capsizing regardless of the circumstances or absolve the master from his responsibilities.

Masters should therefore exercise prudence and good seamanship having regard to the season of the year, weather forecasts and the navigational zone and should take the appropriate action as to speed and course warranted by the prevailing circumstances.

Care should be taken that the cargo allocated to the ship is capable of being stowed so that compliance with the criteria can be achieved.

If necessary the amount should be limited to the extent that ballast weight may be required.

Before a voyage commences care should be taken to ensure that the cargo and sizeable pieces of equipment have been properly stowed or lashed so as to minimize the possibility of both longitudinal and lateral shifting while at sea, under the effect of acceleration caused by rolling and pitching.

Question

State the recommended criteria for passenger and cargo ship.

The following criteria are recommended for passenger and cargo ships:

The area under the righting lever curve (GZ curve) should not be less than 0.055 metre-radians up to q = 30° angle of heel and not less than 0.09 metre-radians up to q = 40° or the angle of flooding q f if this angle is less than 40°.

Additionally, the area under the righting lever curve (GZ curve) between the angles of heel of 30° and 40° or between 30° and q f, if this angle is less than 40°, should not be less than 0.003 metre-radians.

The righting lever GZ should be at least 0.20m. at an angle of heel equal to or greater than 30°

The maximum righting arm should occur at an angle of heel preferably exceeding 30° but not less than 25°

The initial metacentric height GM0 should not be less than 0. 15m.

For ships loaded with timber deck cargoes and provided that the cargo extends longitudinally between superstructures transversely for the full beam of ship after due allowance for a rounded gunwale not exceeding 4 per cent of the breadth of the ship and/or securing the supporting uprights and which remains securely fixed at large angle of heel, an Administration may apply the following criteria in substitution for criteria given in 5.1 above: the area under the righting lever (GZ curve) should not be less than 0.08 metre-radians up to q = 40°or the angle of flooding if this angle is less than 40.

*q f is an angle of heel at which openings in the hull, superstructures or deckhouses which cannot be closed weather tight immerse.

In applying this criterion, small openings through which progressive flooding cannot take place need not be considered as open.

The maximum value of the righting lever (GZ) should be at least 0.25 m.

at all times during a voyage the metacentric height GM0 should be positive after correction for the free surface effects of liquid in tanks, and, where appropriate, the absorption of water by the deck cargo and/or ice accretion on the exposed surfaces. Additionally, in the departure condition the metacentric height should be not less than 0.10 m.

The following additional criteria are recommended for passenger ships:

The angle of heel on account of crowding of passengers to one side as defined in Appendix II 2. (9) should not exceed 10°.

The angle of heel on account of turning should not exceed 10° when calculated using the following formula:

Where:
MR = heeling moment in metre-tons,

Vo = service speed in m. / sec.

L = length of ship at waterline in m.

D = displacement in metric tons,

d = mean draught in m.

KG = height of centre of gravity above keel in m.