Section 2 Application of ice class to hull structures

2.1.1 The application of bow requirements to the stern for Stern First Ice Class Ships in this Section is intended to substitute the FS Rules and PC Rules requirements for the stern of the ship. Application of other ice class rules to the hull structure may be considered, taking into account the philosophy of this Chapter.

2.1.2 For Stern First Ice Class Ships, the requirements of the bow region of the FS Rules or the bow and bow intermediate areas of the PC Rules are to be applied to the stern, taking into account the stern hull form dimensions, extents and requirements of this Chapter.

2.1.3 The application of ice class Rules to the stern and bow may be different if non-standard scenarios are assumed. As a minimum, the stern is to comply with the requirements of a stern for the assigned ice class. See Ch 1, 3.1 Assignment of ice class 3.1.4.

2.1.4 The extent of consideration for the stern hull structure of Stern First Ice Class Ships is from amidships forward in the stern first mode.

2.2.1  0° WL angle (bow). The line that connects points where, in the first instance from the bow, the angle between the waterline and the centreline is zero, commonly termed forward flat of side. For application of FS Rules, this corresponds to the border of the part of the side where waterlines are parallel to the centreline nearest to the bow.

2.2.2  10° WL angle (bow). The line that connects points where, in the first instance from the bow, the angle between the waterline and the centreline is ten degrees.

2.2.3  0° WL angle (stern). The line that connects points where, in the first instance from the stern, the angle between the waterline and the centreline is zero, commonly termed aft flat of side. For application of FS Rules, this corresponds to the forward border of the part of the side where waterlines are parallel to the centreline nearest to the stern.

2.3.1 For application of requirements for PC Rules, the waterline angle, α, at the stern, is to be interpreted using Figure 3.2.2 Interpretation of waterline angles for Stern First Ice Class Ships. The waterline length is to be divided into four sub-regions of equal length. The force F, line load Q, pressure P, and load aspect ratio, AR, are to be calculated with respect to the mid-length position of each sub-region. See Pt 8, Ch 2 Ice Operations - Ice Class of the Rules for Ships.

Figure 3.2.1 Definition of waterline angles

Figure 3.2.2 Interpretation of waterline angles for Stern First Ice Class Ships

2.3.2 For a single propulsion unit installation, the waterline angles are to be interpreted as if the stern centreline were a bow stem. For twin propulsion unit installations, the waterline angles inboard of the centreline of the propulsion unit need not be considered.

2.3.3 For propulsion unit arrangements not indicated in Figure 3.2.2 Interpretation of waterline angles for Stern First Ice Class Ships, the waterline angles are to be specially considered, with respect to the orientation of the structure to the ice load.

2.4.1 Hull strengthening areas are indicated in Figure 3.2.3 Ice-strengthening extents for stern.

Note 1. Ch 3, 2.4 Stern hull areas 2.4.5

Note 2. Ch 3, 2.4 Stern hull areas 2.4.7

Figure 3.2.3 Ice-strengthening extents for stern

2.4.2 If the ship is designed with two sets of UIWL and LIWL for operating forward and stern first in ice, whichever gives the greater requirement is to be considered for hull area definition purposes.

2.4.3 For FS Rule application, the shoulder region is to be divided into two areas. The shoulder ice belt reigon is the area enclosed by the upper extent of the ice belt, X, and lower extent of the ice belt, Y, and bound longitudinally from K to Z. The lower shoulder region Sl is the region bound by the lower extent of the ice belt and a line from the point of intersection of K with the baseline to the point of intersection between W and a vertical line where the 0° WL line intercepts with the LIWL. See Figure 3.2.3 Ice-strengthening extents for stern.

2.4.4 For FS Rule application, the forward and shoulder ice belt regions define the required extent of strengthening for plating. The upper vertical extension of ice strengthening of framing for these ice belt regions is to be taken as 1,0 m above the UIWL. The lower vertical extension of ice strengthening of frames for these ice belt regions is to be taken as 1,6 m below the LIWL. The lower vertical extension of framing for the lower shoulder region need not be greater than the lower extent of the plating.

2.4.5  K is the forward extent (considering the ship in the stern first mode) of the bow region for PC Rule application and the extent of forward strengthening required below the ice belt for FS Rule application. For FS Rule application, K, is defined as five frame spaces forward of the intersection with the foot of the skeg. For PC Rule application or where no skeg is fitted, K may be taken as 0,7b aft (considering the ship in the stern first mode) from the centreline of the propulsion unit slewing column, where b is the half breadth at UIWL at the centreline of the propulsion unit slewing column.

2.4.6 For FS Rule application, the shoulder ice belt is to be considered a continuation of the forward region. The lower shoulder region, Sl, is to have scantlings determined according to midship region requirements.

2.4.7 The aft extent, of the bow intermediate area for PC Rule application or shoulder region for FS Rule application Z, is to be located 0,04 L aft of the point of intersection between the 0° WL line and the LIWL (with the ship in the stern first mode) or at the point of intersection between the 0° WL line and the lower extent of the ice belt region, whichever gives the greater extent of strengthening.

2.5.1 The requirements of Figure 3.2.3 Ice-strengthening extents for stern, based on the hull standard load scenarios, may be applied to ships assigned the notation Icebreaker. However, additional scenarios may need to be considered due to the specialist operational nature of such ships and the particulars of the hull form.

2.5.2 For icebreakers, it is considered that the consistent application of the philosophy of Ch 3, 2.4 Stern hull areas, should be followed alongside the icebreaker’s particular operational and load scenarios.

2.5.3 For icebreakers where the intercept of the 0° WL angle (stern) line with the UIWL and LIWL is near coincident, the value of Z is to be specially considered but is to be taken as 0,08L or 6 m, whichever gives the greater value.

2.5.4 For icebreakers where no parallel mid-body 0° WL angle (stern) exists, the extent of stern strengthening is to be specially considered. In general, the bow intermediate area is to extend aft from K by 0,2L.

2.6.1 For PC Rule application, the bow region is to extend to the bottom shell in way of the propulsion unit(s). For FS Rule application, the forward region is to extend to the bottom shell in way of the propulsion unit(s).

2.6.2 For Stern First Ice Class Ships where different ice classes are used as a strengthening basis for stern first and bow first operating modes, the requirements for the midship region shall be taken from the higher ice class.

2.7.1 For the application of PC Rule requirements, the area factors to be applied to the bow and bow intermediate areas for PC application are given in Table 3.2.1 PC Rule Area Factors for bow and bow intermediate regions applied to the stern of SFIC ships.

2.7.2 For the application of FS Rule requirements, the ice design height to be applied to the bow region is given in Table 3.2.2 FSICR design height for bow region applied to the stern of SFIC ships.

2.8.1 Suitable strengthening is required at the stern, where the stern intersects the upper and lower ice waterlines.

2.8.2 The reinforcement of the stern stem is to be plated and well connected to the internal structure.

2.8.3 For single propulsion unit installations, the stern stem is located at the centreline and should be suitably connected to the centreline girder.

Figure 3.2.4 Example of stern stem arrangement