Section 6 Hull requirements for first-year ice conditions – Ice Classes 1AS FS, 1A FS, 1B FS, 1C FS and 1D

6.1.1 In addition to the requirements of the Finnish-Swedish Ice Class Rules, the following Sections are to be complied with for Ice Class 1AS FS, Ice Class 1A FS, Ice Class 1B FS, Ice Class 1C FS and Ice Class 1D, where applicable. Alternative arrangements to attain similar performance will be considered.

6.2.1 Where a frame intersects a boundary between two of the hull regions the scantling requirements applicable will be those for the forward region if the forward midship boundary is intersected or for the midship region if the aft midship boundary is intersected.

6.2.2 The effective weld area attaching ice frames to primary members is not to be less than the shear area for the frames.

6.2.3 Asymmertrical frames and frames which are not at right angles to the shell (web less than 90 degrees to the shell) shall be supported against tripping by brackets, intercostals, stringers or similar, at a distance not exceeding 1300 mm. For Ice Class 1D, the distance may be increased to 2000 mm. For frames with spans greater than 4 m the extent of anti-tripping supports is to be applied to all regions. For frames with spans less than or equal to 4 m the extent is to be as given in Table 2.6.1 Extent of anti-tripping supports. FEA may be carried out to demonstrate equivalent support of alternative arrangements.

6.3.1 The webs of primary longitudinal members supporting transverse ice frames are to be stiffened and connected to the main or intermediate frames so that the distance, r, between such stiffening is not to be greater than given according to the following formula:

where

or

(b) Midship and aft regions

or

6.3.2 The minimum thickness of the web plating of longitudinal primary members is to comply with the requirements of Pt 3, Ch 10, 4 Construction details for primary members.

6.4.1 The stem is to be made of rolled, cast or forged steel or of shaped steel plates. A sharp edged stem, as shown in Figure 2.6.1 A sharp edged stem, improves the manoeuvrability of the ship in ice. Where a sharp angle stem is fitted, the section modulus as given in Pt 8, Ch 2, 6.4 Stem 6.4.2 and Pt 8, Ch 2, 6.4 Stem 6.4.3 is to apply to the stem section only, otherwise the section modulus may be applied including side plates.

6.4.2 The section modulus of the stem in the fore and aft direction is not to be less than determined in accordance with the following formula:

where

6.4.3 The dimensions of a welded stem constructed as shown in Figure 2.6.1 A sharp edged stem are to be determined in accordance with the following formula:

where

6.4.4 In bulbous bow constructions, the extent of plating below the Ice Light Waterline should be such as to cover that part of the bulb forward of the vertical line originating at the intersection of the Ice Light Waterline and the stem contour at the centreline. A suitably tapered transition piece should be arranged between the reinforced stem plating and keel. However, in no case should the reinforced stem plating extend vertically below the Ice Light Waterline for less than 750 mm. The adjacent strake to the reinforced shaped stem plating of the bulb should be in accordance with the requirements for shell plating.

6.4.5 Where in the ice belt region the radius of the stem or bulb front plating is large, one or more vertical stiffeners are to be fitted in order to meet the section modulus requirement of Pt 8, Ch 2, 6.4 Stem 6.4.2. In addition, vertical ring stiffening will be required for the bulb.

6.4.6 The dimensions of the stem may be tapered to the requirements of Pt 3, Ch 5, 3.3 Stem at the upper deck. The connections of the shell plating to the stem are to be flush.

6.5.1 Where the screwshaft diameter exceeds the Rule diameter, the propeller post is to be correspondingly strengthened, see Pt 3, Ch 6, 7 Sternframes and appendages.

6.6.1 For double hull oil tankers and bulk carriers that are compliant with the IACS Common Structural Rules for Bulk Carriers and Oil Tankers (CSR) , the renewal criteria of the local structure for general corrosion is to be calculated in accordance with the applicable CSR renewal criteria.

6.7.1 Rudder scantlings, posts, rudder horns, solepieces, rudder stocks, steering engine and pintles are to be dimensioned in accordance with Pt 3, Ch 6 Aft End Structure and Pt 3, Ch 13 Ship Control Systems as appropriate. The speed used in the calculations is to be the maximum service speed or that given in Table 2.6.3 Minimum speed, whichever is the greater. When used in association with the speed given in Table 2.6.3 Minimum speed, the rudder profile coefficients are to be taken as 1,1.

6.7.2 For double plate rudders, the minimum thickness of plating and horizontal and vertical webs is to be determined as for shell plating in the midbody region. For the horizontal and vertical webs, the corrosion-abrasion increment, need not be added. For Ice Class 1D, the minimum thickness of plating and webs, of double plate rudders and the extent of application are to be determined as for those in Ice Class 1C FS.

6.7.3 Where an ice class notation is included in the class of a ship, the nozzle construction requirements, as defined in Table 13.3.1 Nozzle constructionin Pt 3, Ch 13 Ship Control Systems, are to be upgraded to include abrasion allowance as follows:

However, the thickness of the shroud plating is not to be less than the shell plating for the aft region taking frame spacing s in the formula as 500 mm.

6.7.4 The scantlings of the stock, pintles, gudgeon and solepiece associated with the nozzle are to be increased on the basis given in Pt 8, Ch 2, 6.7 Rudder and steering arrangements 6.7.1. However, the diameter of the nozzle stock is to be not less than that calculated in the astern condition taking the astern speed as half the speed given in Table 2.6.3 Minimum speed or the actual astern speed, whichever is the greater.

6.7.5 Nozzles with articulated flaps will be subject to special consideration.

6.7.6 For the Ice Classes 1AS FS and 1A FS, the rudder stock and the upper edge of the rudder shall be protected against ice pressure by an ice knife or equivalent means. The ice knife is to extend down to the ice light waterline; this requirement may be waived where this would lead to impracticable ice knifes, e.g. for ships with large draught variations.

6.7.7 For the Ice Classes 1AS FS and 1A FS, 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.

6.7.8 Relief valves for hydraulic pressure are to be effective, see Pt 5, Ch 19, 3.3 Valve and relief valve arrangements. The components of the rudder steering gear are to be able to withstand the yield torque of the rudder stock, see Pt 5, Ch 19, 3.2 Components 3.2.2.