Section 2 Framework for non-standard load scenarios

2.1.1 This Section provides a framework for the determination and application of non-standard load scenarios to ships operating in ice using directional thrust propulsion units, where the operation of the ship/unit differs from that usually assumed from the standard loads scenarios for a Stern First Ice Class Ship indicated in Ch 2 Operational and Load Scenarios.

2.1.2 Non-standard load scenarios may include:

1. Oblique and sideways ice breaking;

2. Dynamic positioning in ice.

2.1.3 The requirements of this Section are not applicable if the standard scenarios are applied.

2.2.1 All modes of operation and ice conditions in which the ship is expected to operate are to be identified.

2.2.2 The combination of modes and ice conditions (operational scenarios) forms the operational envelope.

2.2.3 Standard scenarios may be used as a basis and supplemented by scenarios specific to the ship’s operation.

2.2.4 Operational scenarios shall, as a minimum, define:

1. General mode of operation for the ship;

2. Ice conditions expected in this mode;

3. Evaluation of specific hull and machinery areas loaded.

2.2.5 Operational scenarios are to be made available to LR where they form the basis of the non-standard load scenario definition.

2.3.1 Operational scenarios are to be evaluated by the Operator and designer in terms of frequency and consequence. This constitutes the risk level for each scenario.

2.3.2 Appropriate definitions of frequency and consequence are to be agreed between the designer and Operator.

2.3.3 Operational scenarios are to be ranked in terms of criticality as a combined product scoring of frequency and consequence.

2.3.4 A level of acceptable criticality is to be proposed.

2.3.5 Operational scenarios associated with the highest critical scoring are termed Critical Scenarios.

2.4.1 Critical scenarios require mitigation methods to be proposed in order to reduce the frequency or consequence to an acceptable level.

2.4.2 Mitigation methods for each critical scenario are to be developed. Methods of mitigation may include, but are not limited to:

1. Reappraisal of the scenario from an operational perspective;

2. Use of basis ship data;

3. Use of damage record analysis for ice load determination;

4. Use of established theoretical methods for ice load determination;

5. Use of ice class Rule requirements above Rule minimum levels.

2.5.1 Critical scenarios and associated mitigation methods are to be reviewed by the Operator and designer. If the critical scenarios and mitigation methods form the basis of non-standard load scenarios, they are to be submitted to LR for review.

2.5.2 The review will involve a reassessment of the criticality scoring of the scenarios, in conjunction with the mitigation methods, using the philosophy of Ch 3 Ship Structures and Ch 4 Main and Auxiliary Machinery of these Rules.

2.5.3 Agreed mitigation methods are to form the basis of the load scenarios for application, using the philosophy of the requirements in these Rules and are to be documented as indicated in Ch 6, 3 Scenario document for non standard load scenarios.