Chapter 3 - Subdivision and stability

  3.1.1 Account should be taken of the effect of icing in the stability calculations^footnote.

  3.1.2 Suitable calculations should be carried out and/or tests conducted to demonstrate the following:

• .1 the ship, when operated in ice within approved limitations, during a disturbance causing roll, pitch, heave or heel due to turning or any other cause, should maintain sufficient positive stability; and

• .2 ships of Polar Classes 1 to 3 and icebreakers of all classes, when riding up in ice and remaining momentarily poised at the lowest stem extremity, should maintain sufficient positive stability.

  3.1.3 Sufficient positive stability in paragraphs 3.1.2.1 and 3.1.2.2 means that the ship is in a positive state of equilibrium with a positive metacentric height of at least 150 mm, and a line 150 mm below the edge of the freeboard deck as defined in the applicable LL Convention, is not submerged.

  3.1.4 For performing stability calculations on ships that ride up onto the ice, the ship should be assumed to remain momentarily poised at the lowest stem extremity as follows:

• .1 for a regular stem profile, at the point at which the stem contour is tangent to the keel line;

• .2 for a stem fitted with a structurally defined skeg, at the point at which the stem contour meets the top of the skeg;

• .3 for a stem profile where the skeg is defined by shape alone, at the point at which the stem contour tangent intersects the tangent of the skeg; or

• .4 for a stem profile of novel design, the position should be specially considered.

  3.2.1 All Polar Class ships should be able to withstand flooding resulting from hull penetration due to ice damage of the extent set out in paragraph 3.2.2 and location set out in paragraph 3.2.3, and should remain in a satisfactory condition of equilibrium after such damage, as defined by the IMO instruments applicable to the ship.

  3.2.2 The dimensions of an ice damage penetration should be taken as:

• .1 longitudinal extent 0.045 of deepest ice waterline length if centred forward of the point of maximum beam on the waterline, and 0.015 of waterline length otherwise;

• .2 depth 760 mm measured normal to the shell over the full extent of the damage; and

• .3 vertical extent the lesser of 0.2 of deepest ice draft, or of longitudinal extent.

  3.2.3 The centre of the ice damage may be located at any point between the keel and 1.2 times the deepest ice draft. The vertical extent of damage may be assumed to be confined between the keel and 1.2 times the deepest ice draft. For ships of Polar Classes 5, 6 and 7 not carrying polluting or hazardous cargoes, damage may be assumed to be confined between watertight bulkheads, except where such bulkheads are spaced at less than the damage dimension.

  3.3.1 Subject to paragraphs 3.3.2 and 3.3.3, no Polar Class ship should carry any pollutant directly against the outer shell. Any pollutant should be separated from the outer shell of the ship by double skin construction of at least 760 mm in width.

  3.3.2 All Polar Class ships should have double bottoms over the breadth and the length between forepeak and afterpeak bulkheads. Double bottom height should be in accordance with the rules of the classification societies in force. Double bottoms should not be used for the carriage of pollutants except where a double skin construction complying with paragraph 3.3.1 is provided, or where working liquids, are carried in way of main machinery spaces in tanks not exceeding 20 m³ individual volume.

  3.3.3 Double bottoms in ships of Polar Classes 6 and 7 may be used for the carriage of any working liquids where the tanks are aft of midships and within the flat of bottom.

  3.3.4 All Polar Class ships with icebreaking bow forms and short forepeaks may dispense with double bottoms up to the forepeak bulkhead in the area of the inclined stem, provided that the watertight compartments between the forepeak bulkhead and the bulkhead at the junction between the stem and the keel are not used to carry pollutants.