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For all ships: 👌👇

The following criteria are recommended for passenger and cargo ships:

01. The area under the righting lever curve (GZ Curve) should not be less than 0.055 meter-radians up to θ=30° angle of heel and not less than 0.09 meter-radians up to θ=40° or the angle of flooding θf* if this angle is less than 40°.

02. Additionally, the area under the righting lever curve (GZ curve) between the angles of the heel of 30° and 40° or between 30°and ef, if this angle is less than 40°, should not be less than 0.03 meter-radians.

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

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

05. The initial metacentric height GM0 should not be less than 0.15 m.

06. In addition, for passenger ships, the angle of heel on account of crowding of passengers to one side should not exceed 10°.

07. If anti-rolling devices are installed in a ship, the Administration should be satisfied that the above criteria can be maintained when the devices are in operation.

08. A number of influences such as beam wind on ships with large windage area, icing of topsides, water trapped on deck, rolling characteristics, following seas, etc., adversely affect stability and the Administrations are advised to take these into account, so far as is deemed necessary.

θf is the angle of heel at which openings in the hull superstructures or deckhouses which cannot be closed weathertight immerse. In applying this criterion, small openings through which progressive flooding cannot take place need not be considered as open.

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Intact Stability Criteria for Cargo ships carrying timber deck cargoes:

For ships loaded with timber deck cargoes and provided that the cargo extends longitudinally between superstructures (where there is no limiting superstructure at the after end, the timber deck cargo should extend at least to the after end of the aftermost hatchway) transversely for the full beam of ship after due allowance for a rounded gunwale not exceeding 4% of the breadth of the ship and/or securing the supporting uprights and which remains securely fixed at large angles of heel, the Administration may apply the following criteria which substitute the criteria for all ships:

01. The area under the righting lever curve (GZ curve) should not be less than 0.08 meter-radians up to 0 = 40° or the angle of flooding if this angle is less than 40°.

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

03. 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.

04. Additionally, in the departure condition, the metacentric height should be not less than 0.10 m.

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This chapter discussesthe grain rules proposed by international maritime organization (IMO) for the safe carriage of grain in bulk. The intact stability characteristics of any ship carrying bulk grain must be shown to meet, throughout the voyage, three criteria relating to the moments due to grain shift:

(1) the angle of heel due to the shift of grain shall not be greater than 12° or—in the case of ships constructed on or after 1 January 1994—the angle at which the deck edge is immersed, whichever is the lesser;

(2) in the statical stability diagram, the net or residual area between the heeling arm curve and the righting arm curve up to the angle of heel of maximum difference between the ordinates of the two curves, or 40° or the angle of flooding, whichever is the least, shall be not less than 0.075 metre-radians in all conditions of loading; and

(3) the initial metacentric height, after correction for free surface effects of liquids in tanks, shall not be less than 0.30 m. Before loading bulk grain, the master shall, if so required by the contracting government of the country of the port of loading, demonstrate the ability of the ship at all stages of any voyage to comply with the required stability criteria. After loading, the master shall ensure that the ship is upright before proceeding to sea.

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