Section 10 Hull strengthening requirements for navigation in multi-year ice conditions – Ice Classes PC1, PC2, PC3, PC4, PC5, PC6, PC7 and Icebreaker

10.1.1 The length L_UI is the distance, in m, measured horizontally from the fore side of the stem at the intersection with the upper ice waterline (UIWL) to the after side of the rudder post, or the centre of the rudder stock if there is no rudder post. L_UI is not to be less than 96 per cent, and need not be greater than 97 per cent, of the extreme length of the upper ice waterline (UIWL) measured horizontally from the fore side of the stem. In ships with unusual stern and bow arrangement the length L_UI will be specially considered.

10.1.2 The ship displacement Δ_UI is the displacement, in kilo tonnes, of the ship corresponding to the upper ice waterline (UIWL). Where multiple waterlines are used for determining the UIWL, the displacement is to be determined from the waterline corresponding to the greatest displacement.

10.2.1 The hull of all polar class ships is divided into areas reflecting the magnitude of the loads that are expected to act upon them, see Figure 2.10.1 Extent of hull areas. In the longitudinal direction, there are four regions:

1. bow, (B);

2. bow intermediate, (B _i);

3. midbody, (M), and

4. stern (S).

The bow intermediate, midbody and stern regions are further divided in the vertical direction into three regions:

1. bottom, (b)

2. lower, (l) and

3. icebelt (i).

10.2.2 The upper ice waterline, UIWL, and lower ice waterline, LIWL, are as defined in Pt 8, Ch 2, 2.2 Definitions.

10.2.3 In addition to Figure 2.10.1 Extent of hull areas, at no time is the boundary between the bow and bow intermediate regions to be forward of the intersection point of the line of the stem and the ship baseline.

10.2.4 In addition to Figure 2.10.1 Extent of hull areas, the aft boundary of the bow region need not be more than 0,45L_UI aft of the fore side of the stem at the intersection with the upper ice waterline (UIWL)

10.2.5 The forward boundary of the stern region is to be at least a distance Z from the aft end of L_UI, where Z is 0,7b or 0,15L _UI whichever is greater. b is the distance from the aft end of L_UI to the maximum half breadth at the UIWL and L_UI is defined in Pt 8, Ch 2, 10.1 Definitions.

10.2.6 The boundary between the bottom and lower regions is to be taken at the point where the tangent to the shell is inclined 7° from horizontal.

10.2.7 If a ship is intended to operate astern in ice regions, the aft section of the ship is to be designed based on the bow and bow intermediate hull area requirements. See the Rules for the Classification of Stern First Ice Class Ships, July 2022.

10.2.8 In addition to Figure 2.10.1 Extent of hull areas if the ship is assigned the additional notation Icebreaker the forward boundary of the stern region is to be at least 0,04L forward of the section where the parallel ship side at the upper ice waterline (UIWL) ends.

10.3.1 For ships of all Polar Classes, a glancing impact on the bow is the design scenario for determining the scantlings required to resist ice loads.

10.3.2 The design ice load is characterised by an average pressure, P _a, uniformly distributed over a rectangular load patch of height, b, and width, w.

10.3.3 Within the bow area of all polar classes, and within the bow intermediate icebelt area of polar classes PC6 and PC7, the ice load parameters are functions of the actual bow shape. To determine the ice load parameters, P_a , b and w, it is required to calculate the following ice load characteristics for sub-regions of the bow area; shape coefficient, f _ai, total glancing impact force, F _i, line load, Q _i, and pressure, P _i.

10.3.4 For polar classes PC6 and PC7 the ice load parameters, P_a, b and w, determined as a function of the bow shape in bow region, B, are also to be applied to bow intermediate icebelt region, BIi.

10.3.5 In other ice-strengthened areas, the ice load parameters, P_a , b _NB and w _NB, are determined independently of the hull shape and based on a fixed load patch aspect ratio, AR = 3.6.

10.3.6 Design ice forces calculated according to Pt 8, Ch 2, 10.5 Bow area 10.5.3 are applicable for icebreaking bow forms where the buttock angle γ at the stem is positive and less than 80°, and the normal frame angle β' at the centre of the foremost sub-region, as defined in Figure 2.10.2 Definition of hull angles, is greater than 10°.

10.3.7 Design ice forces calculated according to Pt 8, Ch 2, 10.5 Bow area 10.5.4 are applicable for ships of polar classes PC6 and PC7 and have a bow form with vertical sides. This includes bows where the normal frame angle β' at the considered sub-regions, as defined in Figure 2.10.2 Definition of hull angles are between 0 and 10°.

10.3.8 For ships of polar classes PC6 and PC7 with bulbous bows the design ice forces on the bow are to be determined according to Pt 8, Ch 2, 10.5 Bow area 10.5.4. In addition, the design forces are not to be taken less than those given in Pt 8, Ch 2, 10.5 Bow area 10.5.3, assuming f_a = 0,6 and AR = 1,3.

10.3.9 For ships with bow forms other than those defined in Pt 8, Ch 2, 10.3 Design ice loads – General 10.3.6 to Pt 8, Ch 2, 10.3 Design ice loads – General 10.3.8, design ice forces for any other bow forms are to be specially considered.

10.3.10 Ship structures that are not directly subjected to ice loads may still experience inertial loads of stowed cargo and equipment resulting from ship/ice interaction. These inertial loads are to be considered in the design of these structures.

10.4.1 The parameters defining the glancing impact load characteristics are reflected in the class factors listed in Table 2.10.1 Class factors for icebreaking bow forms and Table 2.10.2 Class factors for vertical side bow forms.

10.5.1 In the bow area, the force, F, line load, Q, pressure, P, and load patch aspect ratio, AR, associated with the glancing impact load scenario are functions of the hull angles measured at the upper ice waterline, UIWL. The influence of the hull angles is captured through calculation of a bow shape coefficient, fa. The hull angles are defined in Figure 2.10.2 Definition of hull angles.

10.5.2 The waterline length of the bow region, C, is generally to be divided along the UIWL into four sub-regions of equal length. The force, F, line load, Q, pressure, P, and load patch aspect ratio, AR, are to be calculated with respect to the mid - length position of each sub-region (each maximum of F, Q and P is to be used in the calculation of the ice load parameters P_a , b and w).

10.5.3 The bow area load characteristics for icebreaking bow forms, as defined in Pt 8, Ch 2, 10.3 Design ice loads – General 10.3.6, are determined as follows:

1. The shape coefficient, fa_i , is to be taken as:

   fai

   =

   fa i,1

   • fa _i,2
   • fa _i,3 whichever is the lesser

   where

   fa i,1

   =

   fa i,2

   =

   fa i,3

   =

   0,60

   i

   =

   sub-region considered

   LUI

   =

   length, as defined in Pt 8, Ch 2, 10.1 Definitions.

   x

   =

   distance from the fore side of the stem at the intersection with the upper ice waterline (UIWL) station under consideration, in metres

   αi

   =

   waterline angle, in degrees, see Figure 2.10.2 Definition of hull angles

   β'i

   =

   normal frame angle, in degrees, see Figure 2.10.2 Definition of hull angles

   ΔUI

   =

   displacement, in kilo tonnes, not to be taken less than 5 as defined in Pt 8, Ch 2, 10.1 Definitions 10.1.2, in kilo tonnes, not to be taken less than 5

   C C

   =

   crushing failure class factor from Table 2.10.1 Class factors for icebreaking bow forms

   C F

   =

   flexural failure class factor from Table 2.10.1 Class factors for icebreaking bow forms

2. Force, F_i :

   

   where

   i

   =

   sub-region considered

   fai

   =

   shape coefficient of sub-region, i

   C C

   =

   crushing failure class factor from Table 2.10.1 Class factors for icebreaking bow forms

   ΔUI

   =

   displacement as defined in Pt 8, Ch 2, 10.1 Definitions 10.1.2, in kilo tonnes, not to be taken less than 5

3. Load patch aspect ratio, AR_i :

   ARi

   =

   7,46 sin ( β'i)

   • AR _i ≥ 1,3

   where

   i

   =

   sub-region considered

   β'i

   =

   normal frame angle of sub-region i, in degrees

4. Line load, Q _i:

   Q i

   =

   MN/m

   where

   i

   =

   sub-region considered

   F i

   =

   force of sub-region i, in MN

   CD

   =

   load patch dimensions class factor from Table 2.10.1 Class factors for icebreaking bow forms

   AR i

   =

   load patch aspect ratio of sub-region i

5. Pressure, P _i:

   P i

   =

   F i 0,22 C D 2 AR i 0,3 MPa

   where

   i	=	sub-region considered
   F i	=	force of sub-region i, in MN
   C D	=	load patch dimensions class factor from Table 2.10.1 Class factors for icebreaking bow forms
   AR i	=	load patch aspect ratio of sub-region i.

10.6.1 In the hull areas other than the bow, the force, F_NB, and line load, Q_NB, used in the determination of the load patch dimensions, b_NB, w_NB, and design pressure, P _a, are determined as follows:

1. Force, F _NB:

   F NB

   =

   0,36C C ΔF MN

   where

   C C

   =

   crushing force class factor from Table 2.10.1 Class factors for icebreaking bow forms

   ΔF

   =

   ship displacement factor

   =

   ∆UI0,64 if ΔUI ≤ CDI

   =

   CDI 0,64 + 0,10 (ΔDI – CDI) if ΔUI ≤ CDI

   ΔUI

   =

   displacement as defined in Pt 8, Ch 2, 10.1 Definitions 10.1.2, in kilo tonnes, not to be taken less than 10

   C DI

   =

   displacement class factor from Table 2.10.1 Class factors for icebreaking bow forms

2. Line Load, Q _NB:

   Q NB

   =

   0,639F NB 0,61 C D MN/m

   where

   F NB

   =

   force from Pt 8, Ch 2, 10.6 Hull areas other than the bow 10.6.1.(a), in MN

   C D

   =

   load patch dimensions class factor from Table 2.10.1 Class factors for icebreaking bow forms.

10.7.1 In the bow area, and the bow Intermediate Icebelt area for ships with class notation PC6 and PC7, the design load patch has dimensions of width, w _B, and height, b _B, defined as follows:

where

10.7.2 In hull areas other than those covered by Pt 8, Ch 2, 10.7 Design load patch 10.7.1, the design load patch has dimensions of width, w _NB, and height, b _NB, defined as follows:

where

10.8.1 The average pressure, P _a, within a design load patch is determined as follows:

where

10.8.2 Areas of higher, concentrated pressure exist within the load patch. In general, smaller areas have higher local pressures. Accordingly, the peak pressure factors listed in Table 2.10.3 Peak pressure factors are used to account for the pressure concentration on localised structural members.

10.9.1 Associated with each hull area is an area factor that reflects the relative magnitude of the load expected in that area. The area factor, AF, for each hull area is listed in Table 2.10.4 Hull area factors (AF) .

10.9.2 In the event that a structural member spans across the boundary of a hull area, the largest hull area factor is to be used in the scantling determination of the member.

10.9.3 Due to their increased manoeuvrability, ships having propulsion arrangements with azimuth thruster(s) or podded propellers are to have specially considered stern icebelt, S_i, and stern lower, S_l, hull area factors. See the Rules for the Classification of Stern First Ice Class Ships, July 2022.

10.9.4 Area factors to be applied to ships assigned the notation Icebreaker are given in Table 2.10.5 Hull area factors (AF) for icebreaker.

10.10.1 The required minimum shell plate thickness, t, is given by:

where

10.10.2 The thickness of shell plating required to resist the design ice load, t _net, depends on the orientation of the framing. The plating net thickness is given by Table 2.10.6 Shell plate thickness.

10.11.1 Framing members of Polar class ships are to be designed to withstand the ice loads defined in Pt 8, Ch 2, 10.3 Design ice loads – General

10.11.2 The term ‘framing member’ refers to transverse and longitudinal local frames, load-carrying stringers and web frames in the areas of the hull exposed to ice pressure, see Figure 2.10.1 Extent of hull areas. Where load-distributing stringers have been fitted, the arrangement and scantlings of these are to be suitably designed.

10.11.3 The strength of a framing member is dependent upon the fixity that is provided at its supports. Fixity can be assumed where framing members are either continuous through the support or attached to a supporting section with a connection bracket. In other cases, simple support is to be assumed unless the connection can be demonstrated to provide significant rotational restraint. Fixity is to be ensured at the support of any framing which terminates within an ice-strengthened area.

10.11.4 The details of framing member intersection with other framing members, including plated structures, as well as the details for securing the ends of framing members at supporting sections, are to be in accordance with Pt 3, Ch 10 Welding and Structural Details.

10.11.5 The effective span of a framing member is to be determined on the basis of its moulded length. If brackets are fitted, the effective span may be reduced in accordance with Pt 3, Ch 3 Structural Design.

10.11.6 When calculating the section modulus and shear area of a framing member, the net thicknesses of the web, flange (if fitted) and attached shell plating are to be used. The shear area of a framing member may include that material contained over the full depth of the member, i.e. web area including portion of flange, if fitted, but excluding attached shell plating.

10.11.7 The actual net effective shear area, A _w, of a transverse or longitudinal local frame is given by:

where

10.11.8 When the cross-sectional area of the attached plate flange exceeds the cross-sectional area of the local frame, the actual net effective plastic section modulus, Z_p, of a transverse or longitudinal frame is given by:

where

h, t _w, t _c and φ_w as given in Pt 8, Ch 2, 10.11 Framing – General 10.11.7

s as given in Pt 8, Ch 2, 10.10 Shell plate requirements 10.10.2

10.11.9 When the cross-sectional area of the local frame exceeds the cross-sectional area of the attached plate flange, the plastic neutral axis is located a distance z _na above the attached shell plate, given by:

and the net effective plastic section modulus, Z_p, of a transverse or longitudinal frame is given by:

10.11.10 In the case of oblique framing arrangement (70° > Ω > 20°, where Ω is defined as given in Pt 8, Ch 2, 10.10 Shell plate requirements 10.10.2), linear interpolation is to be used.

10.12.1 The local frames in bottom structures (i.e. hull areasB_Ib, M_b and S_b) and transversely-framed side structures are to be dimensioned such that the combined effects of shear and bending do not exceed the plastic strength of the member. The plastic strength is defined by the magnitude of midspan load that causes the development of a plastic collapse mechanism. For bottom structures the load patch shall be applied with the dimension b parallel to the frame direction.

10.12.2 The actual net effective shear area of the frame, A _w, as defined in Pt 8, Ch 2, 10.11 Framing – General 10.11.7, is to comply with the following condition:

• A _w ≥ A _t

• need not exceed the lesser of a and b

10.12.4 The scantlings of the local frame are to meet the structural stability requirements of Pt 8, Ch 2, 10.15 Framing – Structural stability.

10.13.1 Longitudinal local frames in side structures are to be dimensioned such that the combined effects of shear and bending do not exceed the plastic strength of the member. The plastic strength is defined by the magnitude of midspan load that causes the development of a plastic collapse mechanism.

10.13.2 The actual net effective shear area of the frame, A _w, as defined in Pt 8, Ch 2, 10.11 Framing – General 10.11.7, is to comply with the following condition:

A _w ≥ A _L

10.13.3 The actual net effective plastic section modulus of the plate/stiffener combination, Z _p, as defined in Pt 8, Ch 2, 10.11 Framing – General 10.11.8 or Pt 8, Ch 2, 10.11 Framing – General 10.11.9, is to comply with the following condition:

• Z _p ≥ Z _pL

AF, K _s, P _a, b ₁, a and σ_y are as given in Pt 8, Ch 2, 10.13 Framing – Longitudinal local frames in side structures 10.13.2.

10.13.4 The scantlings of the longitudinals are to meet the structural stability requirements of Pt 8, Ch 2, 10.15 Framing – Structural stability.

10.14.1 Web frames and load-carrying stringers are to be designed to withstand the ice load patch as defined in Pt 8, Ch 2, 10.8 Pressure within the design load patch. The load patch is to be applied at locations where the capacity of these members under the combined effects of bending and shear is minimised.

10.14.2 Web frames and load-carrying stringers are to be dimensioned to take into account the combined effects of shear and bending. Where the structural configuration is such that members do not form part of a grillage system, the appropriate peak pressure factor, K _i, from Table 2.10.3 Peak pressure factors is to be used. Special attention is to be paid to the shear capacity in way of lightening holes and cut-outs in way of intersecting members.

10.14.3 For determination of scantlings on load carrying stringers, web frames supporting local frames, or web frames supporting load carrying stringers forming part of a structural grillage system, appropriate methods as outlined in Pt 8, Ch 2, 10.28 Direct calculations are normally to be used.

10.14.4 The scantlings of web frames and load-carrying stringers are to meet the structural stability requirements of Pt 8, Ch 2, 10.15 Framing – Structural stability.

10.15.1 To prevent local buckling in the web, the ratio of web height, h _w, to net web thickness, t _wn, of any framing member is not to exceed:

For flat bar sections:

For bulb, tee and angle sections:

10.15.2 Framing members for which it is not practicable to meet the requirements of Pt 8, Ch 2, 10.15 Framing – Structural stability 10.15.1(e.g. load carrying stringers or deep web frames) are required to have their webs effectively stiffened. The scantlings of the web stiffeners are to ensure the structural stability of the framing member. The minimum net web thickness for these framing members is given by:

10.15.3 In addition, the following is to be satisfied:

• t _wn ≥

10.15.4 To prevent local flange buckling of welded profiles, the following are to be satisfied:

1. The flange width, b _f, in mm, is not to be less than five times the net thickness of the web, t _wn.

2. The flange outstand, b _o, in mm, is to meet the following requirement:

   
   where

   t fn	=	net thickness of flange, in mm
   σy	=	minimum upper yield stress of the material, in N/mm2.

10.16.1 Plated structures are those stiffened plate elements in contact with the hull and subject to ice loads. These requirements are applicable to an inboard extent which is the lesser of:

1. web height of adjacent parallel web frame or stringer; or

2. 2,5 times the depth of framing that intersects the plated structure.

10.16.2 The thickness of the plating and the scantlings of attached stiffeners are to be such that the degree of end fixity necessary for the shell framing is ensured.

10.16.3 The stability of the plated structure is to adequately withstand the ice loads defined in Pt 8, Ch 2, 10.8 Pressure within the design load patch.

10.17.1 Effective protection against corrosion and ice-induced abrasion is recommended for all external surfaces of the shell plating for Polar Class ships.

10.17.2 The values of corrosion/abrasion additions, t_s, to be used in determining the shell plate thickness are listed in Table 2.10.7 Corrosion/abrasion additions for shell plating. See the Rules for the Manufacture, Testing and Certification of Materials, July 2022, Ch 15, 2.13 Ice coatings.

10.17.3 Polar Class ships are to have a minimum corrosion/abrasion addition of t_s = 1,0 mm applied to all internal structures within the ice strengthened hull areas, including plated members adjacent to the shell, as well as stiffener webs and flanges.

10.17.4 Steel renewal for ice strengthened structures is required when the gauged thickness is less than t_n + 0,5 mm.

10.18.1 Steel grades of plating for hull structures are to be not less than those given in Table 2.10.9 Steel grades for weather exposed plating to Table 2.10.11 Steel grades for weather exposed plating based on the as-built thickness, the Polar Class and the material class of structural members given in Table 2.10.8 Material classes for structural members of polar ships.

10.18.2 Material classes specified in Table 2.2.1 Material classes and grades in Pt 3, Ch 2 Materials, are applicable to Polar Class ships regardless of the ship's length. In addition, material classes for weather and sea exposed structural members and for members attached to the weather and sea exposed plating are given in Table 2.10.8 Material classes for structural members of polar ships. Where the material classes in Table 2.10.8 Material classes for structural members of polar ships and those in Table 2.2.1 Material classes and grades in Pt 3, Ch 2 Materials differ, the higher material class is to be applied.

10.18.3 Steel grades for all plating and attached framing of hull structures and appendages situated below the level of 0,3 m below the lower waterline, as shown in Figure 2.10.6 Steel grade requirements for submerged and weather exposed shell plating, are to be obtained from Table 2.2.2 Steel grades inPt 3, Ch 2 Materials, based on the material class for Structural Members in Table 2.10.8 Material classes for structural members of polar ships above, regardless of Polar Class.

10.18.4 Steel grades for all weather exposed plating of hull structures and appendages situated above the level of 0,3 m below the lower ice waterline, as shown in Figure 2.10.6 Steel grade requirements for submerged and weather exposed shell plating, are to be not less than given in Table 2.10.9 Steel grades for weather exposed plating to Table 2.10.11 Steel grades for weather exposed plating.

10.18.5 Castings are to have specified properties consistent with the expected service temperature for the cast component.

10.19.1 A ramming impact on the bow is the design scenario for the evaluation of the longitudinal strength of the hull.

10.19.2 Intentional ramming is not considered as a design scenario for ships which are designed with vertical side bow forms or bulbous bow forms, see Pt 8, Ch 2, 1.4 Application for multi-year ice conditions 1.4.4. Hence the longitudinal strength requirements given in Pt 8, Ch 2, 10.23 Longitudinal strength criteria are not to be considered for ships with stem angle γ_stem equal to or greater than 80°.

10.19.3 Ice loads are only to be combined with still water loads. The combined stresses are to be compared against permissible bending and shear stresses at different locations along the ship's length. In addition, sufficient local buckling strength is also to be verified.

10.20.1 The design vertical ice force at the bow, F_IB, is to be taken as the lesser of F_{IB, 1} or F_{IB, 2}:

where

10.21.1 The design vertical ice shear force, F _I, along the hull girder is to be taken as:

where

1. Positive shear force

   C f

   =

   0,0 between the aft end of LUI and 0,6LUI from aft

   C f

   =

   1,0 between 0,9LUI from aft and the forward end of L UI

2. Negative shear force

   Cf

   =

   0,0 at the aft end of LUI

   Cf

   =

   -0,5 between 0,2LUI and 0,6 LUI from aft

   Cf

   =

   0,0 between 0,8LUI from aft and the forward end of LUI

   LUI

   =

   length, as defined in Pt 8, Ch 2, 10.1 Definitions 10.1.2 in metres

Intermediate values are to be determined by linear interpolation.

10.21.2 The applied vertical shear stress, τ_a, is to be determined along the hull girder in a similar manner as in Pt 3, Ch 4 Longitudinal Strength by substituting the design vertical ice shear force for the design vertical wave shear force.

10.22.1 The design vertical ice bending moment, M_I, along the hull girder is to be taken as:

where

• Intermediate values are to be determined by linear interpolation.

10.22.2 The applied vertical bending stress, σ_a, is to be determined along the hull girder in a similar manner as in Pt 3, Ch 4 Longitudinal Strength, by substituting the design vertical ice bending moment for the design vertical wave bending moment. The ship still water bending moment is to be taken as the permissible still water bending moment in sagging condition.

10.23.1 The strength criteria provided in Table 2.10.12 Longitudinal strength criteria are to be satisfied. The design stress is not to exceed the permissible stress.

10.24.1 The stem and stern frame are to be suitably designed. The stem and stern requirements of the Finnish-Swedish Ice Class Rules are to be additionally considered, see Pt 8, Ch 2, 1 Strengthening requirements for navigation in ice – Application of requirements.

10.25.1  Rudder scantlings, posts, rudder horns, solepieces, rudder stocks, steering engines, 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 2.10.13 Minimum speed, whichever is the greater. When used in association with the speed given in Table 2.10.13 Minimum speed, the rudder profile coefficients are to be taken as 1,1.

10.25.2 For the astern condition the actual astern speed or half the minimum speed defined in Table 2.10.13 Minimum speed is to be used, whichever is greater.

10.25.3 The section modulus of the solepiece calculated in accordance with Pt 8, Ch 2, 10.25 Rudders 10.25.1 and Pt 8, Ch 2, 10.25 Rudders 10.25.2 need not be greater than three times the section modulus of the solepiece, calculated in accordance with Pt 3, Ch 13 Ship Control Systems using the actual maximum service speed.

10.25.4 Local scantlings of rudders are to be determined considering that the rudder belongs to the stern ice belt/ice belt lower, depending on rudder location with respect to the lower extent of the ice belt. Rudder local plating and framing located above the lower extent of the main ice belt are to be dimensioned using the stern ice belt area factor applicable to the relevant Polar Class. Rudder local plating and framing located below the lower extent of the main ice belt are to be dimensioned using the stern lower ice belt area factor applicable to the relevant Polar Class.

10.25.5 For scantlings of the rudder blade the plate thickness is to be determined in accordance with Pt 8, Ch 2, 10.10 Shell plate requirements using the rudder web frame spacing. The aspect ratio of the panel under consideration is to be used to determine the appropriate selection of formulae for transverse or longitudinally framed plating. Where the aspect ratio is 1,0, the panel is to be considered transversely framed.

10.25.6 The vertical and horizontal web thickness is not to be less than 0,7t_R, but is not to be taken as less than 8 mm, where t_R is the rudder plate thickness.

10.25.7 The mainpiece is to be dimensioned in accordance with Pt 3, Ch 13 Ship Control Systems, utilising the basic stock diameter derived using in the minimum speed in Table 2.10.13 Minimum speed.

10.26.1 All appendages are to be designed to withstand forces appropriate for the location of their attachment to the hull structure or their position within a hull area.

10.27.1 Local design details are to be suitably designed to transfer ice-induced loads to supporting structure (bending moments and shear forces).

10.27.2 The loads carried by a member in way of cut-outs are not to cause instability. Where necessary, the structure is to be stiffened.

10.28.1 Direct calculations are not to be utilised as an alternative to the analytical procedures prescribed for the shell plating and local frame requirements given in Pt 8, Ch 2, 10.10 Shell plate requirements to Pt 8, Ch 2, 10.13 Framing – Longitudinal local frames in side structures.

10.28.2 Direct calculations are to be used for load carrying stringers and web frames forming part of a grillage system.

10.28.3 Where direct calculation is used to check the strength of structural systems, the load patch specified in Pt 8, Ch 2, 10.3 Design ice loads – General is to be applied, without being combined with any other loads. The load patch is to be applied at locations where the capacity of these members under the combined effects of bending and shear is minimised. Special attention is to be paid to the shear capacity in way of lightening holes and cut-outs in way of intersecting members.

10.28.4 The strength evaluation of web frames and stringers may be performed based on linear or non-linear analysis. Recognised structural idealisation and calculation methods are to be applied, see Pt 3, Ch 1, 2 Direct calculations. In the strength evaluation, the guidance given in Pt 8, Ch 2, 10.28 Direct calculations 10.28.5 and Pt 8, Ch 2, 10.28 Direct calculations 10.28.6 may generally be considered.

10.29.1 All welding within ice-strengthened areas is to be of the double continuous type.

10.29.2 Continuity of strength is to be ensured at all structural connections.