Section 12 Requirements for Icebreaker(+)

12.1.1 Where the notation Icebreaker(+) is assigned, the arrangement, powering and scantlings of the hull structure and propulsion machinery are to be determined based on the operational profile that corresponds to that which the icebreaker is envisaged to undertake as determined in the ship specific scenario document.

12.1.2 The assignment of the notation Icebreaker(+) is in addition to the requirements of Pt 8, Ch 2, 10 Hull strengthening requirements for navigation in multi-year ice conditions – Ice Classes PC1, PC2, PC3, PC4, PC5, PC6, PC7 and Icebreaker and Pt 8, Ch 2, 11 Machinery strengthening requirements for navigation in multi-year ice conditions – Ice Classes PC1, PC2, PC3, PC4, PC5, PC6, PC7 and Icebreaker and is assigned in addition to the ice class notations given in Table 2.1.1 Polar class descriptions. See Pt 8, Ch 2, 1.5 Icebreakers.

12.2.1 The operational profile to be used for the basis of assignment of the notation Icebreaker(+) is to be derived from the icebreaker’s function, as selected from Pt 8, Ch 2, 12.4 Typical operational profiles.

12.2.2 The operational profile is only used to select a design basis. It is the responsibility of the Owner and/or Builder to determine the appropriate operational profile of the icebreaker.

12.3.1 For assignment of the notation Icebreaker(+), the operational envelope criteria are to be submitted, which may include the following information, where applicable:

1. the level icebreaking capability, in terms of speed and ice thickness;

2. the turning capability in level ice, in terms of diameter and ice thickness; and

3. the ramming capability, in terms of speed and ice condition.

12.3.2 In addition to the information submitted in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.1, a scenario document, which is ship specific, is required to document the operational profile and is to include details of the scenarios selected for deriving and applying ice loads.

12.3.3 The scenario document is to address the requirements in Pt 8, Ch 2, 10 Hull strengthening requirements for navigation in multi-year ice conditions – Ice Classes PC1, PC2, PC3, PC4, PC5, PC6, PC7 and Icebreaker and Pt 8, Ch 2, 11 Machinery strengthening requirements for navigation in multi-year ice conditions – Ice Classes PC1, PC2, PC3, PC4, PC5, PC6, PC7 and Icebreaker and provide justification for deviation from those requirements.

12.3.4 The following is to be contained within the submitted scenario document:

1. icebreaker function;

2. details of ice conditions assumed;

3. operational scenarios for hull and propulsion machinery;

4. identification of critical hull and propulsion machinery scenarios;

5. description of propulsion machinery and/or hull loading areas with reasons for selection;

6. proposed strengthening standards for each load area;

7. arrangement of propulsion devices;

8. derived load data-based full scale measurement or other predictive means; and

9. details of, and justification for, deviation from the Rules.

12.3.5 In addition to the information submitted in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.4, an ice pressure plan that indicates the design ice pressures used for the determination of the hull structure is to be submitted.

12.3.6 The operational envelope criteria is to be placed on board the ship.

12.4.1 Typical operational profiles may bederived from the icebreaker function. Primary icebreaker functions are described in Table 2.12.1 Primary icebreaker functions. These functions are to form the basis of operational scenarios as required in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.4. Where an alternative function is selected a description of the icebreaker’s operational functions is to be included in the scenario document.

12.5.1 Consideration is to be given to the protection of fuel tanks and other tanks with harmful substances, both in terms of thermal insulation and ice impact protection. A double bottom and double side tanks are to be fitted as specified in Pt 4, Ch 9, 1.2 Application and ship arrangement 1.2.17. However, double side tanks may not be required for small icebreakers (typically less than 60 m), nor complete double bottom height in way of complex hullform arrangements in the fore and aft ends or heeling tanks.

12.5.2 Consideration is to be given to minimise transom sterns, as these hinder the icebreaker’s ability to back in ice, and in particular the navigation of ice ridges. A transom stern should not normally extend below the Upper Ice Waterline. Where this cannot be avoided, the transom should be kept as narrow as possible and the scantlings of plating and stiffeners are to be as required for the stern section.

12.5.3 The requirements are based on an effective icebreaker bow form. Icebreaking angles vary depending on the icebreaking form; however, in general, the bow stem angle is not to be greater than 45^o, and the bow waterline angle not greater than 40^o, see Figure 2.12.1 Icebreaker stem angles. Where flare of the side shell amidships is proposed, it is recommended that the slope of the side be at least 8^o.

12.5.4 Ice arresters (ice skeg) are recommended for all icebreakers to prevent riding up of the bow and submergence of the aftermost deck edge.

12.5.5 For icebreakers provided with a heel inducing system, it is recommended that the depth of the icebreaker be such that immersion of the deck edge does not occur when the ship, whilst floating at the Upper Ice Waterline, is heeled to an angle of 5° greater than the nominal capacity of the system or 15°, whichever is the greater.

12.5.6 For icebreakers intended to navigate continuously in thick multi-year ice, i.e. PC1, PC2 and PC3, and in relation to the icebreaker function, consideration should be given to the mass of the icebreaker to enable effective ice breaking.

12.5.7 For icebreakers installed with podded propulsion or azimuth thrusters, see the Rules for the Classification of Stern First Ice Class Ships, July 2022

12.6.1 An ice pressure plan is to be submitted as required in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.5. The ice pressure is to consider the adjustment of area factors for additional ice interaction scenarios as well as the crushing failure class factors due to the increased impact speed as well as application with due cognisance of low displacements.

12.6.2 The area factors associated with the ice pressure plan in Pt 8, Ch 2, 12.6 Hull strength 12.6.1 are, as a minimum, to comply with the hull area factors given in Table 2.10.4 Hull area factors (AF) for the ice class assigned.

12.6.3 In addition to the ice pressure plan required in Pt 8, Ch 2, 12.5 General arrangement 12.5.1, consideration is to be given to the enhancement of longitudinal strength based on the operational profile. The utilisation factor, η, in Table 2.10.12 Longitudinal strength criteria, is to be adjusted accordingly.

12.7.1 Icebreakers are to be equipped with means of propulsion that meet the operational envelope criteria. Demonstration of suitable propulsion power for the operational envelope criteria as specified in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.1, as appropriate, may be from any of the following or other appropriate methods:

1. theoretical formulation, as given in Pt 8, Ch 2, 12.7 Propulsion and machinery arrangements 12.7.2 and Pt 8, Ch 2, 12.7 Propulsion and machinery arrangements 12.7.3;

2. technical investigations based on engineering principles;

3. service experience at the operating ice conditions; and

4. ice model tests.

Consideration should be given to the applicable speed in relation to the ice thickness, as provided in Pt 8, Ch 2, 12.3 Information to be submitted 12.3.1, and the operational profile.

12.7.2 The propulsion power, at 2 knots, for icebreakers may be expressed as follows, where the ice thickness and icebreaker breadth form the dominant role:

where

12.7.3 The propulsion power, at 2 knots, for icebreakers may be expressed as follows, where Pt 8, Ch 2, 12.7 Propulsion and machinery arrangements 12.7.3 is modified to account for the hullform:

Where

12.7.4 The formulae given in Pt 8, Ch 2, 12.7 Propulsion and machinery arrangements 12.7.2 and Pt 8, Ch 2, 12.7 Propulsion and machinery arrangements 12.7.3 are based on the broad fleet of icebreaker designs (60≤L≤140m and 15≤B≤28) and level ice thicknesses (0.5≤h≤2m). Adjustments may therefore be required to account for specific propulsion arrangements, alternative speed criteria, size-mass effects, other L/B ratios and ice conditions.

12.7.5 The propulsion power condition is to be considered, whereby 100 per cent of the rated ahead speed is available for a minimum of 30 minutes. A minimum astern power condition is to be considered, whereby 70 per cent of the rated astern speed is available for a minimum of 30 minutes.

12.7.6 Consideration should be given to machinery protection against over-speeding, excess torque, overloading and overheating.

12.7.7 Propulsion system redundancy is to be considered. Where a machinery redundancy (PMR, SMR or PSMR) notation is to be assigned in addition to an Icebreaker(+) notation, the requirements of Pt 5, Ch 22 Propulsion and Steering Machinery Redundancy are to be complied with.

12.7.8 Icebreakers are prone to additional noise and vibration. Conditions when icebreaking are to be considered when applying the rules, see Pt 5, Ch 1, 4.3 Resilient mountings and Pt 7, Ch 13 On-shore Power Supplies.

12.8.1 Rudder posts, rudder horns, solepieces, rudder stocks and pintles are to be dimensioned in accordance with Pt 8, Ch 2, 10.25 Rudders. The minimum speed for rudder dimensioning purposes is to be taken as the speed required for the assigned Polar Class as a minimum. Increases above the minimum speed may be required based on the operational profile.

12.8.2 Steering arrangements are to be in accordance with Pt 8, Ch 2, 11.24 Steering arrangements. The arrangements are to comply with the assigned Polar Class as a minimum. Increases above the minimum requirements may be required based on the operational profile.

12.9.1 For escort icebreakers, arrangements for towing are to be provided, including a notch shape in the stern and provision of two chock pipes and two bitts. Consideration should be given for stern plating and framing to be strengthened to withstand impact loads for escorted ship collisions, as well as the propulsion and steering gear layout and protection from contact with bulbous bows. See Pt 4, Ch 3, 7 Towing arrangements.

12.10.1 Where a winterisation notation is assigned in compliance with the Rules for the Winterisation of Ships, July 2022, the following features are to be additionally considered:

1. bridge wings are to be fully enclosed;

2. ice removal measures, through heating arrangements, are to be provided to access routes to towing equipment for escort icebreakers;

3. provisions for evacuation onto ice;

4. additional search lights for mooring, astern manoeuvring and towing operations;

5. consideration of a red (flashing) navigation light to be used to indicate when an escort icebreaker is stopped;

6. provisions to prevent water freezing in water and fluid systems, including research laboratories and services;

7. consideration of ice accretion in damage condition; and

8. protection from ice accretion by enclosed aft walkways for icebreakers with an exposed aft deck.