Section 2 Definitions

2.1.1 It is assumed that the majority of ships operating in ice are designed with sterns capable of operating astern in ice. For icebreakers, such operations may involve the propellers acting in reverse during manoeuvring operations. However, the primary icebreaking mode of operation for such vessels is bow first.

2.1.2 Ship definitions in the Rules are used to enable a more accurate description of the operation of Stern First Ice Class ships and a comparison with other ship types operating in ice. The definitions are limited to the application of the Rules only.

2.2.1 Bow forms, as described in Table 1.2.1 Ship types in relation to ship operations and ice conditions of the Rules, are described in further detail below. Specific bow types are not a requirement of the Rules. Various bow forms may be adopted for stern first operation in ice. Bow forms are typically selected based on the operational profile and can be broadly categorised into four groups, see Table 1.2.1 Bow types:

1. Open water bow (may include bulbous bows).

2. Optimised open water bow for ice navigation (may include ice-strengthened bulbous bows).

3. Conventional ice-strengthened bow.

4. Icebreaking bow.

Table 1.2.1 Bow types

Bow type	Illustrative bow shapes	Typical ice conditions for design of bow shape (bow first)	Typical ship type application
Open water bow		Open water	Unstrengthened for ice
Optimised open water bow for ice navigation		Open water/young ice/thin first-year ice	Ships assigned SFIC notation
Conventional ice strengthened bow		Open water/young ice/thin first-year ice	Conventional ice class ships Ships assigned SFIC notation
Icebreaking bow		Thick first-year ice/old ice	Icebreakers Conventional icebreaking ships Ships assigned SFIC notation

2.2.2 An open water bow is designed for optimal hydrodynamic performance in open water. There are no considerations given to ice, either in terms of ice resistance or icebreaking capability. No additional strengthening is given above that required to resist the hydrodynamic and hydrostatic loads.

2.2.3 A conventional ice-strengthened bow is designed as a compromise between the required hydrodynamic performance in open water and performance in ice (varying on the anticipated ice conditions and related to the ice class). An icestrengthened bow has additional strengthening in terms of distribution and size of stiffening and shell plating thickness to resist ice loads.

2.2.4 An optimised open water bow for ice navigation is optimised for hydrodynamic performance in open water. Strengthening is incorporated for ice operation.

2.2.5 Icebreaking bows are primarily designed for optimum performance in ice, not open water. Their purpose is to break ice by bending, and may be either spoon or wedge in shape. Icebreaking bows may be incorporated into ships such as icebreakers, sub-Arctic or Arctic-going cargo ships.

2.2.6 Stern First Ice Class Ships typically may have bow types as indicated in Ch 1, 2.2 Bow types 2.2.1, Ch 1, 2.2 Bow types 2.2.1 and Ch 1, 2.2 Bow types 2.2.1 TB.

2.3.1  Stern First Ice Class Ship stern: Ships which are expected to be operated stern first in ice have sterns which are specially designed to enable continuous icebreaking in level ice, enable flow from the propeller to pass along the hull length (hull washing) and incorporate directional thrust propulsion unit(s) which are external to the hull. Consequently, the shape of such sterns usually incorporates a shallow stern angle (with a function much like that of a conventional ice breaker stern) with convex waterlines. In addition, the fairing between this area, the propeller and the run aft enable flow from the propeller stream along the sides of the hull. For crossing ridges, such ships will typically flush the ice by rotating the propulsion units and using the propeller wash to clear the ridge keel.

2.3.2  Conventional icebreaker stern: Typically, icebreakers are designed with sterns which can withstand high impact loads. For these ships it is assumed that the vessel may back into ice, during backing and ramming operations. Such sterns are not primarily designed to break ice continuously stern first.

2.3.3  Ice-strengthened stern: Vessels designed to navigate in ice generally with the assistance of an icebreaker, or in areas served by icebreakers, have ice-strengthened sterns. The ice-strengthening in the stern area of such ships is generally concerned with impacts from loose ice displaced by the vessel or from impacts by the ship on edges of newly broken ice channels. The shape of an ice-strengthened stern is generally no different from that of a vessel designed for open water.

2.3.4 Stern First Ice Class Ships are expected to have sterns as described in Ch 1, 2.3 Stern types 2.3.1. The standard load scenarios have been validated for these sterns only.

2.3.5 In addition to stern types indicated in Figure 1.2.1 Stern shape, Stern First Ice Class ships may incorporate a skeg or skegs. Typically, these appendages are incorporated for course keeping and directional stability in light ice conditions. The skeg is not considered as a typical ‘ice skeg’, in that the skeg is not intended to act as a stopper to prevent beaching or for breaking of large ice floes where confined ice crushing would require increased strength. When operating bow first, the skeg effectively limits the size of ice floes that may impact the propeller. The skeg may be of faired or plated type.

Figure 1.2.1 Stern shape

2.4.1 For interpretation of international conventions, Table 1.2.3 International convention, and Rule references indicates recommended approaches that have been adopted by National Administrations for stern first ice class ships, specifically Finnish and Russian Flags. However, it is recommended that the National Administration to which the ship is registered be consulted to ensure appropriate regulatory interpretation.

2.4.2 For navigational related conventions, it is the intention that equipment and arrangements for operating stern first be considered in addition to bow first operation. This may result in the duplication of some equipment items, such as navigation lights.