Section 2 General hull requirements for navigation in ice – All ice classes

2.1.1 The following Sections are to be complied with for all Ice Classes, where applicable. Alternative arrangements to attain similar performance will be specially considered.

2.1.2 The ballast capacity of the ship is to be sufficient to give adequate propeller immersion in all ice navigating conditions without trimming the ship in such a manner that the actual waterline at the bow is below the lower ice waterline.

2.1.3 Fresh water and sea-water ballast tanks, the tops of which are situated above the design ballast waterline and adjacent to the shell, which are intended to be used in ice and cold navigating conditions, are to be provided with means to prevent freezing. Measures are to be provided to demonstrate that they protect against the following:

1. hull structural damage from pumping water creating a vacuum beneath a layer of ice across the top of the water in the tank, and

2. hull structural damage from ice expansion, and

3. engineering systems, such as piping systems and components, damage from ice expansion or ice blockage, and

4. engineering systems, such as piping systems and components, damage from ice pieces melting or dislodging from upper sections of the tank.

Heating coils are considered an effective means for tanks entirely above the waterline. Heating coils or other effective means such as continuous circulation, air bubbling and/or tank pressure/engineering systems alarms are considered effective for tanks partially below the waterline. Alternatively, demonstration that the above hazards have been mitigated is to be submitted through theoretical calculations, service experience, experimental tests, or a combination thereof.

2.1.4 These Rules are formulated for both transverse and longitudinal framing systems but it is recommended that, whenever practicable, transverse framing is selected.

2.1.5 These Rules assume that when approaching ice infested waters, the ship's speed will be reduced appropriately. The vertical extent of ice strengthening for ships intended to operate at speeds exceeding 15 knots in areas containing isolated ice floes will be specially considered.

2.1.6 An icebreaking ship is to have a hull form at the fore end adapted to break ice effectively. It is recommended that bulbous bows are not fitted to Ice Class 1AS ships.

2.1.7 The stern of an icebreaking ship is to have a form such that broken ice is effectively displaced.

2.1.8 Where it is desired to make provision for short tow operations, the bow area is to be suitably reinforced. Similarly, icebreakers may require local reinforcement in way of the stern fork.

2.1.9 Shell strakes in way of ice strengthening area for plates are to be grade B/AH.

2.1.10 To prevent unintended contact and permit close tow operations, provision of a bow ice knife (plate fitted between stem and bulbous bow) is not recommended for ships intended to navigate with icebreaker escort.

2.2.1 The upper and lower ice waterlines upon which the design of the vessel has been based is to be indicated in the classification certificate. The upper ice waterline (UIWL) is to be defined by the maximum draughts fore, amidships and aft. The lower ice waterline (LIWL) is to be defined by the minimum draughts fore, amidships and aft.

2.2.2 The lower ice waterline is to be determined with due regard to the vessel's ice-going capability in the ballast loading conditions (e.g. propeller submergence).

2.2.3 The upper ice waterline (UIWL) and lower ice waterline (LIWL) are to be indicated on the plans. For navigation in certain geographical areas, the relevant National Authority may require the maximum Ice Class draught to be marked on the ship in a specified manner.

2.2.4  Displacement ∆ is the displacement at the upper ice waterline (UIWL) when floating in water having a relative density of 1,0. For first-year ice class Rules, the displacement is in tonnes. For multi-year ice class Rules, the displacement is in kilo tonnes.

2.2.5  Shaft power, P ₀ , is the maximum propulsion shaft power, in kW, for which the machinery is to be classed.

2.3.1 Rudder stoppers working on the rudder blade or rudder head are to be fitted to ships assigned the notations Ice Class 1AS FS, 1AS FS(+), 1A FS, 1A FS(+) and to ships assigned Polar Class (PC) notations.

2.3.2 The design ice force on the rudder, based on the maximum rudder torque, shall be transmitted to the rudder stoppers without damage to the steering system.

2.3.3 The design ice force on the rudder stopper shall be considered as F_s = M_x/d_s, where M_x is the maximum design rudder torque determined according to the requirements of the Finnish-Swedish Ice Class Rules for ships assigned the notations Ice Class 1AS FS, 1A FS and Pt 8, Ch 2, 10.25 Rudders for ships assigned Polar Class (PC) notations, and d_s is the distance between the centre of the rudder stock and the rudder stopper. The allowable stresses given in Table 2.2.1 Allowable stress in rudder stopper, ice knife and supporting structure in way of rudder stopper, ice knife are not to be exceeded in the stoppers, their supporting structure, and the throat of the stopper welds.

2.3.4 Rudder stoppers are to be arranged such that protection of the steering gear is provided two degrees before the maximum travel of the steering gear.

2.3.5 The steering gear, rudder stock and upper edge of the rudder are to be protected from loads from ice impact when operating astern. A robust ice knife or equivalent means of protecting the rudder head and upper edge of the rudder is to be fitted to ships assigned the notations Ice Class 1AS FS, 1A FS, and to ships assigned Polar Class (PC) notations.

2.3.6 The width of the ice knife shall provide protection to the rudder two degrees either side of the centreline. The lower edge of the ice knife should extend below the upper edge of the rudder’s trailing edge or lower ice waterline, whichever is the lowest. For a ship with large draught variations, the ice knife shall extend below the upper edge of the rudder’s trailing edge.

2.3.7 The design force for the ice knife, F_k, shall be determined as F_k = p h l, where p is the ice pressure and h is the ice load height calculated according to the stern hull area according to the requirements of the Finnish-Swedish Ice Class Rules for ships assigned the notations Ice Class 1AS FS, 1A FS or Pt 8, Ch 2, 10.7 Design load patch and Pt 8, Ch 2, 10.8 Pressure within the design load patch for ships assigned Polar Class (PC) notations respectively. The load length, l, is to be considered according to the ice knife construction, but in general is to be taken as the support frame transverse spacing.

2.3.8 For the Ice Classes 1AS FS,1A FS and Polar Class (PC) notations, due regard is to be paid to the excessive load caused by the rudder being forced out of the midship position when backing into an ice ridge. When vessels are intended to operate with significant time in astern operation, then the hull strength is to be based on the method used in the forward region; however, due consideration may be given to the anticipated power in this mode of operation.

2.3.9 For plated structures, the thickness of the boundaries of the ice knife structure is not to be less than that of the rudder side plating.