Section 7 Ice classification

7.1.1 For ships with the Ice classification notations 1AS, 1A, 1B and 1C, there are no additional survey requirements over and above those for commercial ships with the same notations, see Ch 16, 7.2 Ice class 1AS, 1A, 1B and 1C.

7.1.2 For ships with the Ice classification notations 1AS*, 1A*, 1B* and 1C*, there are additional survey requirements as these ships are not designed for regular operation in ice, see Ch 16, 7.3 Ice class 1AS*, 1A*, 1B* and 1C*.

7.2.1 One of the key requirements of the ice class notations is the material grade. This is determined by the design air temperature in which the ship is expected to operate. It is important to use notch tough grades such as D, E or even F, to reduce the probability of crack initiation and failure of the structure at low temperatures. Therefore it is essential that any modifications or repairs be made using the correct material as indicated on the approved plans.

7.2.2 It is also important to ensure that modifications or repairs do not introduce stress concentrations in the structure. The general guidelines of Ch 3 Construction Procedurescan be followed to achieve this. Particular attention should be paid to temporary attachments, transition from ice strengthened to regular structure and finished weld quality, which can be difficult to achieve in the closely spaced ice framing.

7.2.3 Damage following operation in ice or assistance from icebreakers is also of concern. Ships designed for regular operation in ice are to be inspected at docking surveys during the normal survey cycle. Structural damage should be dealt with in a similar manner to other damages from grounding or collision, see Ch 14 Distortion and deformation.

7.2.4 Even apparently minor damage which appears on external examination to be to the plating only, may cause significant damage to internal framing. The internal region in way of the damage should always be inspected.

7.2.5 Cracks may also occur in areas adjacent to damage, at areas of high stress concentration such as cut outs in primary members.

7.2.6 Appendages such as propellers, rudders, bilge keels, stabilisers and sonar domes are vulnerable to damage and should be inspected, even though they are outside the ice belt. Particular attention should be paid to areas where the stress is high such as bilge keel ends, propeller blade roots and rudder stock to rudder connection.

7.3.1 In addition to the requirements listed in Ch 16, 7.2 Ice class 1AS, 1A, 1B and 1C, ships that have an additional * notation may have different design requirements for the plating. The assumption is that these ships only require an emergency operational capability in ice and the plating is designed such that permanent deflection of plating in the ice belt can take place. Permanent deflection is only permitted where there are no significant in-plane stresses where a deformed plate could lead to premature failure.

7.3.2 The design assumptions for primary and secondary stiffening are unchanged.

7.3.3 Following operation in ice, these ships are to be subject to an external survey of the plating in way of the ice belt. Where there is evidence of damage an inspection is to be made of the adjacent internal structure. Areas of significant plating deformation are to be replaced. Internal structure in way of the deformed plate should also be examined for deformation and where necessary, renewed.