ICE CLASS REGULATIONS 2008 (FINNISH-SWEDISH ICE CLASS RULES)

Transcription

1 Finnish Maritime Administration BULLETIN 10/ ICE CLASS REGULATIONS 2008 (FINNISH-SWEDISH ICE CLASS RULES) The Finnish Maritime Administration has, by a decision of 8 December 2008, issued the Ice Class Regulations (Ice Class Rules) of 2008, pursuant to section 4.1 of the Act on the Ice Classes of Ships and Icebreaker Assistance (1121/2005). The decision and the new Ice Class Regulations of 2008 enter into force on 15 December The rules in section 6 concerning the ship's propulsion machinery have been totally renewed in the new Ice Class Rules. The Ice Class rules of 2008 shall be applied to ships on the building of which the contract has been signed on 1 January 2010 or thereafter. From 15 December 2008 the Ice Class Rules of 2008 can, however, be applied to ships on the building of which the contract has been signed on 15 December 2008 or thereafter. Enclosed are the Finnish Maritime Administration Decision on Ice Class Regulations and the application thereof and the Ice Class Regulations of Director of Maritime Safety Tuomas Routa Senior Maritime Inspector Jorma Kämäräinen For further information please contact: The Technical Division This Bulletin 13/ supersedes Bulletins: 12/ No. 2530/30/2008 ISSN This Bulletin is Finnish Maritime Administration Address Mail Phone Fax available from: Registrar s Office Porkkalankatu 5 PO Box kirjaamo@fma.fi FI Helsinki FI Helsinki

2 2 FINNISH MARITIME REGULATION Date: ADMINISTRATION No.: 2530/30/2008 Contents: Based on: Period of validity: Ice class regulations and the application thereof Act on the Ice Classes of Ships and Icebreaker Assistance (1121/2005), section 4.1 December 15, 2008 until further notice FINNISH MARITIME ADMINISTRATION DECISION ON ICE CLASS REGULATIONS AND THE APPLICATION THEREOF Adopted in Helsinki on 8 December 2008 Pursuant to section 4.1 of the Act of 22 December 2005 on the Ice Classes of Ships and Icebreaker Assistance (1121/2005), the Finnish Maritime Administration has decided the following: Section 1 The Ice Class Regulations of 2008 and the application thereof The Finnish Maritime Administration has issued more detailed regulations (the Ice Class Regulations of 2008), enclosed to this decision, on the requirements concerning the structure, engine output and other ice navigation properties of ships belonging to the different ice classes, on the methods for determining ice classes, and on differences between ice classes, referred to in section 4.1 of the Act on the Ice Classes of Ships and Icebreaker Assistance (1121/2005). The Ice Class Regulations (Ice Class Rules) of 2008 shall be applied to ships on the building of which the contract has been signed on 1 January 2010 or thereafter. The rules in chapter 1 (General) and 2 (Ice class draught) in the Ice Class Rules of 2008 apply to all ships irrespective of their year of build. Section 2 Application of the 2002 Ice Class Rules A ship the keel of which has been laid or which has been at a similar stage of construction on 1 September 2003 or thereafter, but on the building of which the contract has been signed before 1 January 2010 shall comply with the FMA Ice Class Rules of 2002 ( No. 5/30/2002, FMA Bulletin no. 13/ ), as amended. From 15 December 2008 the Ice Class Rules of 2008 can, however, be applied to ships on the building of which the contract has been signed on 15 December 2008 or thereafter. Section 3 Application of the 1985 Ice Class Rules A ship the keel of which has been laid or which has been at a similar stage of construction on 1 November 1986 or thereafter, but before 1 September 2003 shall comply with the

3 3 requirements in the Board of Navigation Rules for Assigning Ships Separate Ice-Due Classes of 1985, as amended. On the ship owner's request, however, the requirements concerning engine output in the FMA Ice Class Rules of 2008 can also be applied to the ship. A ship of ice class IA Super or IA the keel of which has been laid or which has been at a similar stage of construction before 1 September 2003 shall, however, comply with the requirements in section of the FMA Ice Class Rules of 2008 on January 1 in the year when 20 years have elapsed since the year the ship was delivered, whichever occurs the latest. Section 4 Application of the 1971 Ice Class Rules The requirements of Annex I or section 10 of the Board of Navigation Rules for Assigning Ships Separate Ice-Due Classes of 1985 ( No. 1260/71/307), as amended, apply to a ship the keel of which has been laid or which has been at a similar stage of construction before 1 November 1986, depending on the age of the ship. On the ship owner s request, the requirements on engine output in the Board of Navigation Rules for Assigning Ships Separate Ice-Due Classes of 1985 ( No. 2575/85/307) or in the FMA Ice Class Rules of 2008 may be applied to such a ship. A ship of ice class IA Super or IA the keel of which has been laid or which has been at a similar stage of construction before 1 September 2003 shall, however, comply with the requirements in section of the FMA Ice Class Rules of 2008 on 1 January in the year when 20 years have elapsed since the year the ship was delivered, whichever occurs the latest Section 5 Ice class draughts and the required minimum engine output to be indicated in the certificate of classification The maximum and minimum ice class draught fore, amidships and aft and the required minimum engine output shall be indicated in the certificate of classification. Section 6 Maximum draught when assistance restrictions are in force The draught of a ship must not exceed the maximum permissible ice class draught when the ship is sailing to or from a Finnish port assistance restrictions, requiring as a minimum ice class IC, IB or IA of ships, are in force. Section 7 Entry into force This decision and the enclosed Ice Class Regulations of 2008 enter into force on 15 December Helsinki, 8 December 2008 Director-General Markku Mylly Director of Maritime Safety Tuomas Routa

4 1 ICE CLASS REGULATIONS 2008 FINNISH-SWEDISH ICE CLASS RULES 2008 Adopted in Helsinki on 8 December 2008 (No. 2530/30/2008) TABLE OF CONTENTS 1 GENERAL Ice classes 4 2 ICE CLASS DRAUGHT Upper and lower ice waterlines Maximum and minimum draught fore and aft 4 3 ENGINE OUTPUT Definition of engine output Required engine output for ice classes IA Super, IA, IB and IC Definitions New ships Existing ships of ice class IB and IC Existing ships of ice class IA Super or IA Other methods of determining K e or R CH 9 4 HULL STRUCTURAL DESIGN General Regions Ice load Height of load area Ice pressure Shell plating Vertical extension of ice strengthening (ice belt) Plate thickness in the ice belt Frames Vertical extension of ice strengthening Transverse frames Section modulus Upper end of transverse framing Lower end of transverse framing Longitudinal frames General on framing The attachment of frames to supporting structures Support of frames against tripping for ice class IA Super, for ice class IA in the forward and midship regions and for ice classes IB and IC in the forward region of the ice-strengthened area Ice stringers Stringers within the ice belt 17

5 Stringers outside the ice belt Deck strips Web frames Load Section modulus and shear area Direct calculations Bow Stem Arrangements for towing Stern Bilge keels 23 5 RUDDER AND STEERING ARRANGEMENTS 23 6 PROPULSION MAHCINERY Scope Symbols Design ice conditions Materials Materials exposed to sea water Materials exposed to sea water temperature Design loads Design loads on propeller blades Maximum backward blade force F b for open propellers Maximum forward blade force F f for open propellers Loaded area on the blade for open propellers Maximum backward blade ice force F b for ducted propellers Maximum forward blade ice force F f for ducted propellers Loaded area on the blade for ducted propellers Maximum blade spindle torque Q smax for open and ducted propellers Load distribution for blade loads Number of ice loads Axial design loads for open and ducted propellers maximum ice thrust on propeller T f and T b for open and ducted propellers Design thrust along the propulsion shaft line for open and ducted propellers Torsional design loads Design ice torque on propeller Q max for open propellers Design ice torque on propeller Q max for ducted propellers Ice torque excitation for open and ducted propellers Design torque along propeller shaft line Blade failure load Design Design principles Propeller blade Calculation of blade stresses Acceptability criterion Fatigue design of propeller blade Acceptability criterion for fatigue Propeller bossing and CP mechanism Propulsion shaft line Shafts and shafting components Azimuthing main propulsors 42

6 Vibrations Alternative design methods Scope Loading Design levels 43 7 MISCELLANEOUS MACHINERY REQUIREMENTS Starting arrangements Sea inlet and cooling water systems 44 Annex I Annex II The validity of the powering requirement in section for ice classes IA Super, IA, IB and IC, and verification of calculated powering requirements 45 Required engine output for a ship of ice class IB or IC the keel of which has been laid or which has been at a similar stage of construction before 1 September Annex III Ice class draught marking 48

7 4 1 GENERAL 1.1 Ice classes Under section 3 of the Act on the Ice Classes of Ships and Icebreaker Assistance (1121/2005) ships are assigned to ice classes as follows: 1. ice class IA Super; ships with such structure, engine output and other properties that they are normally capable of navigating in difficult ice conditions without the assistance of icebreakers; 2. ice class IA; ships with such structure, engine output and other properties that they are capable of navigating in difficult ice conditions, with the assistance of icebreakers when necessary; 3. ice class IB; ships with such structure, engine output and other properties that they are capable of navigating in moderate ice conditions, with the assistance of icebreakers when necessary; 4. ice class IC; ships with such structure, engine output and other properties that they are capable of navigating in light ice conditions, with the assistance of icebreakers when necessary; 5. ice class II; ships that have a steel hull and that are structurally fit for navigation in the open sea and that, despite not being strengthened for navigation in ice, are capable of navigating in very light ice conditions with their own propulsion machinery; 6. ice class III; ships that do not belong to the ice classes referred to in paragraphs ICE CLASS DRAUGHT 2.1 Upper and lower ice waterlines The upper ice waterline (UIWL) shall be the highest waterline at which the ship is intended to operate in ice. The line may be a broken line. The lower ice waterline (LIWL) shall be the lowest waterline at which the ship is intended to operate in ice. The line may be a broken line. 2.2 Maximum and minimum draught fore and aft The maximum and minimum ice class draughts at fore and aft perpendiculars shall be determined in accordance with the upper and lower ice waterlines. Restrictions on draughts when operating in ice shall be documented and kept on board readily available to the master. The maximum and minimum ice class draughts fore, amidships and aft shall be indicated in the classification certificate. For ships built on or after 1 July 2007, if the summer load line in fresh water is located at a higher level than the UIWL, the ship s sides are to be provided with a warning triangle and with an ice class draught mark at the maximum permissible ice class draught amidships (see Annex III). Ships built before 1 July 2007 shall be provided with such a marking, if the UIWL is below the summer load line, not later than the first scheduled dry docking after 1 July 2007.

8 5 The draught and trim, limited by the UIWL, must not be exceeded when the ship is navigating in ice. The salinity of the sea water along the intended route shall be taken into account when loading the ship. The ship shall always be loaded down at least to the LIWL when navigating in ice. Any ballast tank, situated above the LIWL and needed to load down the ship to this water line, shall be equipped with devices to prevent the water from freezing. In determining the LIWL, regard shall be paid to the need for ensuring a reasonable degree of ice-going capability in ballast. The propeller shall be fully submerged, if possible entirely below the ice. The forward draught shall be at least: ( Δ) h o [m] but need not exceed 4h o, Δ is displacement of the ship [t] on the maximum ice-class draught according to 2.1. h o is level ice thickness [m] according to ENGINE OUTPUT 3.1 Definition of engine output The engine output P is the maximum output the propulsion machinery can continuously deliver to the propeller(s). If the output of the machinery is restricted by technical means or by any regulations applicable to the ship, P shall be taken as the restricted output. 3.2 Required engine output for ice classes IA Super, IA, IB and IC The engine output shall not be less than that determined by the formula below and in no case less than 1000 kw for ice class IA, IB and IC, and not less than 2800 kw for IA Super Definitions The dimensions of the ship and some other parameters are defined below: L m length of the ship between the perpendiculars L BOW m length of the bow L PAR m length of the parallel midship body B m maximum breadth of the ship T m actual ice class draughts of the ship according to A wf m 2 area of the waterline of the bow α degree the angle of the waterline at B/4 ϕ 1 degree the rake of the stem at the centerline ϕ 2 degree the rake of the bow at B/4 D P m diameter of the propeller H M m thickness of the brash ice in mid channel H F m thickness of the brash ice layer displaced by the bow

9 6 Figure 3-1. Determination of the geometric quantities of the hull. If the ship has a bulbous bow, then ϕ 1 = New Ships To be entitled to ice class IA Super, IA, IB or IC, a ship the keel of which is laid or which is at a similar stage of construction on or after 1 September 2003 shall comply with the following requirements regarding its engine output. The engine output requirement shall be calculated for two draughts. Draughts to be used are the maximum draught amidship referred to as UIWL and the minimum draught referred to as LIWL, as defined in 2.2. In the calculations the ship's parameters which depend on the draught are to be determined at the appropriate draught, but L and B are to be determined only at the UIWL. The engine output shall not be less than the greater of these two outputs. K e shall be taken as follows: P ( R /1000) Number of CP or electric or hydraulic FP propellers propulsion machinery propeller 1 propeller propellers propellers /2 CH = Ke [ kw], (3.1) DP These K e values apply for conventional propulsion systems. Other methods may be used for determining the required power for advanced propulsion systems (see 3.2.4). R CH is the resistance in Newton of the ship in a channel with brash ice and a consolidated surface layer:

10 LT A RCH = C1+ C2 + C3Cμ ( HF + HM ) ( B+ CψHF ) + C4LPARHF + C5 B 2 L wf, (3.2) C μ = 0.15cosϕ 2 + sinψsinα, C μ is to be taken equal or larger than 0.45 C ψ = ψ 2.115, and C = 0 if ψ 45 ψ H F = ( H B) M 0.5 H M = 1.0 for ice classes IA and IA Super = 0.8 for ice class IB = 0.6 for ice class IC C 1 and C 2 take into account a consolidated upper layer of the brash ice and are to be taken as zero for ice classes IA, IB and IC. For ice class IA Super: BL C = f + + f B+ f L + f BL For a ship with a bulbous bow, ϕ 1 shall be taken as 90. f 1 = 23 N/m 2 g 1 = 1530 N f 2 = 45.8 N/m g 2 = 170 N/m f 3 = 14.7 N/m g 3 = 400 N/m 1.5 f 4 = 29 N/m 2 C 3 = 845 kg/(m 2 s 2 ) C 4 = 42 kg/(m 2 s 2 ) C 5 = 825 kg/s 2 tanϕ 2 ψ = arctan sinα ( ϕ )( ) PAR 1 1 T BOW 4 2 B + 1 T C2 = ( ϕ 1)( g1+ g2b) + g B B 2 L BOW 3 LT 2 B is not to be taken as less than 5 and not to be taken as more than 20. Further information on the validity of the above formulas can be found in Annex I together with sample data for the verification of powering calculations. If the ship s parameter values are beyond

11 8 the ranges defined in Table I-1 of Annex I, other methods for determining R CH shall be used as defined in Existing ships of ice class IB or IC To be entitled to retain ice class IB or IC a ship, on which the ice class regulations 1985 ( , No. 2575/85/307 as amended) apply, shall comply with the required minimum engine output as defined in section of the ice class regulations For ease of reference the provisions for ice classes IB and IC of section of the ice class regulations 1985 are given in Annex II of these regulations Existing ships of ice class IA Super or IA To be entitled to retain ice class IA Super or IA a ship, the keel of which has been laid or which has been at a similar stage of construction before 1 September 2003, shall comply with the requirements in section above at the following dates: - 1 January 2005 or - 1 January in the year when 20 years has elapsed since the year the ship was delivered, whichever occurs the latest. When, for an existing ship, values for some of the hull form parameters required for the calculation method in section are difficult to obtain, the following alternative formulae can be used: 2 2 LT R CH = C1 + C2 + C3 ( HF + HM ) ( B HF) + C4LHF + C5 B 2 for ice class IA, C 1 and C 2 shall be taken as zero. For ice class IA Super, ship without a bulb, C 1 and C 2 shall be calculated as follows: BL C= f fb+ fl+ fbl ( ) 1 1 T B B, (3.3) 4 T C2 = 3.52( g1+ g2b) + g B B 2 L For ice class IA Super, ship with a bulb, C 1 and C 2 shall be calculated as follows: BL C= f fb+ fl+ fbl ( ) 1 1 T B C2 6.67( g1 g2b) g T = B B L,

12 9 LT 2 B f 1 = 10.3 N/m 2 g 1 = 1530 N f 2 = 45.8 N/m g 2 = 170 N/m f 3 = 2.94 N/m g 3 = 400 N/m 1.5 f 4 = 5.8 N/m 2 C 3 = 460 kg/(m 2 s 2 ) C 4 = 18.7 kg/(m 2 s 2 ) C 5 = 825 kg/s 2 3 is not to be taken as less than 5 and not to be taken as more than Other methods of determining K e or R CH For an individual ship, in lieu of the K e or R CH values defined in and 3.2.3, the use of K e or R CH values based on more exact calculations or values based on model tests may be approved. Such an approval will be given on the understanding that it can be revoked if experience of the ship s performance in practice motivates this. The design requirement for ice classes is a minimum speed of 5 knots in the following brash ice channels: IA Super H M = 1.0 m and a 0.1 m thick consolidated layer of ice IA = 1.0 m IB = 0.8 m IC = 0.6 m 4 HULL STRUCTURAL DESIGN 4.1 General The method for determining the hull scantlings is based on certain assumptions concerning the nature of the ice load on the structure. These assumptions are from full scale observations made in the northern Baltic. It has thus been observed that the local ice pressure on small areas can reach rather high values. This pressure may be well in excess of the normal uniaxial crushing strength of sea ice. The explanation is that the stress field in fact is multiaxial. Further, it has been observed that the ice pressure on a frame can be higher than on the shell plating at midspacing between frames. The explanation for this is the different flexural stiffness of frames and shell plating. The load distribution is assumed to be as shown in Figure 4-1.

13 10 Figure 4-1. Ice load distribution on a ship s side. For the formulae and values given in this section for the determination of the hull scantlings more sophisticated methods may be substituted subject to approval by the administration or the classification society. If scantlings derived from these regulations are less than those required by the classification society for an unstrengthened ship, the latter shall be used. NB. The frame spacing and spans defined in the following text are normally assumed to be measured in a vertical plane parallel to the centreline of the ship. However, if the ship's side deviates more than 20 from this plane, the frame distances and spans shall be measured along the side of the ship Regions For the purpose of this section, the ship's hull is divided into regions as follows (see also Figure 4-2): Forward region: From the stem to a line parallel to and 0.04 L aft of the forward borderline of the part of the hull the waterlines run parallel to the centerline. For ice classes IA Super and IA the overlap over the borderline need not exceed 6 meters, for ice classes IB and IC this overlap need not exceed 5 meters. Midship region: From the aft boundary of the Forward region to a line parallel to and 0.04 L aft of the aft borderline of the part of the hull the waterlines run parallel to the centerline. For ice classes IA Super and IA the overlap over the borderline need not exceed 6 meters, for ice classes IB and IC this overlap need not exceed 5 meters. Aft region: From the aft boundary of the Midship region to the stern. L shall be taken as the ship's rule length used by the classification society.

14 11 Figure 4-2. Ice strengthened regions of the hull. 4.2 Ice load Height of load area An ice-strengthened ship is assumed to operate in open sea conditions corresponding to a level ice thickness not exceeding h o. The design height (h) of the area actually under ice pressure at any particular point of time is, however, assumed to be only a fraction of the ice thickness. The values for h o and h are given in the following table. Ice Class h o [m] h [m] IA Super IA IB IC Ice pressure The design ice pressure is determined by the formula: [ ] p = cd cp ca p0 MPa, (4.1) c d is a factor which takes account of the influence of the size and engine output of the ship. It is calculated by the formula: c d a k + b =, 1000 k = Δ P 1000

15 12 a and b are given in the following table: a b R e g i o n Forward Midship & Aft k 12 k > 12 k 12 k > Δ is the displacement of the ship at maximum ice class draught [t] (see 2.1). P is the actual continuous engine output of the ship [kw] (see 3.1). c p is a factor which takes account of the probability that the design ice pressure occurs in a certain region of the hull for the ice class in question. The value of c p is given in the following table: Ice Class IA Super IA IB IC R e g i o n Forward Midship Aft c a is a factor which takes account of the probability that the full length of the area under consideration will be under pressure at the same time. It is calculated by the formula: c a = 47-5l 44 a ; maximum 1.0 ; minimum 0.6, l a shall be taken as follows: Structure Type of framing l a [m] Shell Transverse Frame spacing Longitudinal 2 frame spacing Frames Transverse Frame spacing Longitudinal Span of frame Ice stringer Span of stringer Web frame 2 web frame spacing p o is the nominal ice pressure; the value 5.6 MPa shall be used.

16 Shell plating Vertical extension of ice strengthening (ice belt) The vertical extension of the ice belt shall be as follows (see Figure 4-2): Ice Class Above UIWL [m] Below LIWL [m] IA Super IA IB IC In addition, the following areas shall be strengthened: Fore foot: For ice class IA Super, the shell plating below the ice belt from the stem to a position five main frame spaces abaft the point the bow profile departs from the keel line shall have at least the thickness required in the ice belt in the midship region. Upper forward ice belt: For ice classes IA Super and IA on ships with an open water service speed equal to or exceeding 18 knots, the shell plate from the upper limit of the ice belt to 2 m above it and from the stem to a position at least 0.2 L abaft the forward perpendicular, shall have at least the thickness required in the ice belt in the midship region. A similar strengthening of the bow region is advisable also for a ship with a lower service speed, when it is, e.g. on the basis of the model tests, evident that the ship will have a high bow wave. Sidescuttles shall not be situated in the ice belt. If the weather deck in any part of the ship is situated below the upper limit of the ice belt (e.g. in way of the well of a raised quarter decker), the bulwark shall be given at least the same strength as is required for the shell in the ice belt. The strength of the construction of the freeing ports shall meet the same requirements Plate thickness in the ice belt For transverse framing the thickness of the shell plating shall be determined by the formula: f p t = s + t (4.2) [ ] 1 PL 667 c mm σ y For longitudinal framing the thickness of the shell plating shall be determined by the formula: s is the frame spacing [m] p PL = 0.75 p [MPa], p is as given in ppl t = 667 s + tc [ mm], (4.3) f σ 2 y

17 14 f f 4.2 = 1.3 ; maximum 1.0 ( h/ s+ 1.8) = ; when h/s 1 ( h/ s) f 2 = (h/s); when 1 h/s < 1.8 h is as given in σ y is yield stress of the material [N/mm 2 ], for which the following values shall be used: σ y = 235 N/mm 2 for normal-strength hull structural steel σ y = 315 N/mm 2 or higher for high-strength hull structural steel If steels with different yield stress are used, the actual values may be substituted for the above ones if accepted by the classification society. t c is increment for abrasion and corrosion [mm]; normally t c shall be 2 mm; if a special surface coating, by experience shown capable to withstand the abrasion of ice, is applied and maintained, lower values may be approved. 4.4 Frames Vertical extension of ice strengthening The vertical extension of the ice strengthening of the framing shall be at least as follows: Ice Class Region Above UIWL [m] From stem to 0.3L 1.2 abaft it IA Super IA, IB, IC Below LIWL [m] To double bottom or below top of floors Abaft 0.3L from stem Midship Aft From stem to 0.3L abaft it Abaft 0.3L from stem Midship Aft Where an upper forward ice belt is required (see 4.3.1), the ice-strengthened part of the framing shall be extended at least to the top of this ice belt.

18 15 Where the ice-strengthening would go beyond a deck or a tanktop by no more than 250 mm, it can be terminated at that deck or tanktop Transverse frames Section modulus The section modulus of a main or intermediate transverse frame shall be calculated by the formula: Z p s h l 6 3 = 10 cm mt σ y, (4.4) p is ice pressure as given in [MPa] s is frame spacing [m] h is height of load area as given in [m] l is span of the frame [m] 7mo m t = 7-5 h/ l σ y is yield stress as in [N/mm 2 ] m o takes the boundary conditions into account. The values are given in the following table:

19 16 The boundary conditions are those for the main and intermediate frames. Load is applied at mid span. Where less than 15% of the span, l, of the frame is situated within the ice-strengthening zone for frames as defined in 4.4.1, ordinary frame scantlings may be used Upper end of transverse framing The upper end of the strengthened part of a main frame and of an intermediate ice frame shall be attached to a deck of an ice stringer (section 4.5). Where a frame terminates above a deck or a stringer which is situated at or above the upper limit of the ice belt (section 4.3.1), the part above the deck or stringer may have the scantlings required by the classification society for an unstrengthened ship and the upper end of an intermediate frame may be connected to the adjacent frames by a horizontal member having the same scantlings as the main frame. Such an intermediate frame can also be extended to the deck above, and if this is situated more than 1.8 metre above the ice belt, the intermediate frame need not be attached to that deck, except in the Forward region Lower end of transverse framing The lower end of the strengthened part of a main frame and of an intermediate ice frame shall be attached to a deck, tanktop or ice stringer (section 4.5). Where an intermediate frame terminates below a deck, tanktop or ice stringer which is situated at or below the lower limit of the ice belt (section 4.3.1), the lower end may be connected to the adjacent main frames by a horizontal member of the same scantlings as the frames Longitudinal frames The section modulus of a longitudinal frame shall be calculated by the formula: Z f f p h l = 10 cm m σ y (4.5) The shear area of a longitudinal frame shall be: A 3 f p h l = 10 cm 2σ (4.6) y This formula is valid only if the longitudinal frame is attached to supporting structure by brackets as required in In the formulae given above: f 3 is a factor which takes account of the load distribution to adjacent frames: f 3 = (1-0.2 h/s)

20 17 f 4 is a factor which takes account of the concentration of load to the point of support, f 4 = 0.6 p is ice pressure as given in [MPa] h is height of load area as given in [m] s is frame spacing [m] The frame spacing shall not exeed 0.35 metre for ice class IA Super or IA and shall in no case exceed 0.45 metre. l is span of frame [m] m is a boundary condition factor; m = 13.3 for a continuous beam; the boundary conditions deviate significantly from those of a continuous beam, e.g. in an end field, a smaller boundary factor may be required. σ y is yield stress as in [N/mm 2 ] General on framing The attachment of frames to supporting structures Within the ice-strengthened area all frames shall be effectively attached to all the supporting structures. A longitudinal frame shall be attached to all the supporting web frames and bulkheads by brackets. When a transversal frame terminates at a stringer or deck, a bracket or similar construction is to be fitted. When a frame is running through the supporting structure, both sides of the web plate of the frame are to be connected to the structure (by direct welding, collar plate or lug). When a bracket is installed, it has to have at least the same thickness as the web plate of the frame and the edge has to be appropriately stiffened against buckling Support of frames against tripping for ice class IA Super, for ice class IA in the forward and midship regions and for ice classes IB and IC in the forward region of the ice-strengthened area Frames which are not at a straight angle to the shell shall be supported against tripping by brackets, intercostals, stringers or similar at a distance not exceeding 1300 mm. The frames shall be attached to the shell by double continuous weld. No scalloping is allowed (except when crossing shell plate butts). The web thickness of the frames shall be at least one half of the thickness of the shell plating and at least 9 mm. Where there is a deck, tanktop or bulkhead in lieu of a frame, the plate thickness of this shall be as above, to a depth corresponding to the height of adjacent frames. 4.5 Ice stringers Stringers within the ice belt The section modulus of a stringer situated within the ice belt (see 4.3.1) shall be calculated by the formula:

21 18 The shear area shall be: Z f p h l = 10 cm m σ y (4.7) A 3 f p h l = 10 cm 2σ, (4.8) y p is ice pressure as given in [MPa] h is height of load area as given in [m] The product p h shall not be taken as less than l is span of the stringer [m] m is a boundary condition factor as defined in f 5 is a factor which takes account of the distribution of load to the transverse frames; to be taken as 0.9 σ y is yield stress as in Stringers outside the ice belt The section modulus of a stringer situated outside the ice belt but supporting ice-strengthened frames shall be calculated by the formula: f p h l Z h l = ( 1 s s) 10 cm m σ y (4.9) The shear area shall be: 3 f p h l =, (4.10) 6 A hs ls 2σ y 4 2 ( 1 ) 10 cm p is ice pressure as given in [MPa] h is height of load area as given in [m] The product p h shall not be taken as less than l is span of stringer [m] m is boundary condition factor as defined in l s is the distance to the adjacent ice stringer [m] h s is the distance to the ice belt [m] f 6 is a factor which takes account of load to the transverse frames; to be taken as 0.95

22 19 σ y is yield stress of material as in Deck strips Narrow deck strips abreast of hatches and serving as ice stringers shall comply with the section modulus and shear area requirements in and respectively. In the case of very long hatches the classification society may permit the product p h to be taken as less than 0.30 but in no case as less than Regard shall be paid to the deflection of the ship's sides due to ice pressure in way of very long hatch openings when designing weatherdeck hatch covers and their fittings. 4.6 Web frames Load The load transferred to a web frame from an ice stringer or from longitudinal framing shall be calculated by the formula: F = p h S [MN], (4.11) p is ice pressure as given in [MPa], in calculating c a however, l a shall be taken as 2S. h is height of load area as given in [m] The product p h shall not be taken as less than 0.30 S is distance between web frames [m] In case the supported stringer is outside the ice belt, the force F shall be multiplied by (1- h s /l s ), h s and l s shall be taken as defined in Section modulus and shear area If a web frame is represented by the structure model shown in Figure 4-3, the section modulus and shear area shall be calculated by the formulae:

23 20 Figure 4-3. Shear area: A 3 α Q 10 σ 4 2 = cm, (4.12) y Q is maximum calculated shear force under the load F, as given in 4.6.1, or k 1 F, k 1 = 1 + 1/2 (l F /l) 3-3/2 (l F /l) 2 or = 3/2 (l F /l) 2-1/2 (l F /l) 3 whichever is greater For the lower part of the web frame the smallest l F within the ice belt shall be used. For the upper part the biggest l F within the ice belt shall be taken. α is as given in the table below σ y is yield stress of material as in F is as in Section modulus: Z M = 2 σ y 1 ( γ AAa) 10 cm, (4.13) M is maximum calculated bending moment under the load F, as given in 4.6.1, or k2 F l, k 2 = 1/2 (l F /l) 3-3/2 (l F /l) 2 + (l F /l)

24 21 γ is given in the table below A is required shear area obtained by using k 1 = 1 + 1/2 (l F /l) 3-3/2 (l F /l) 2 A a is actual cross sectional area of the web frame Factors α and γ can be obtained from the table below A f /A w α γ A f is cross section area of free flange A w is cross section area of web plate Direct calculations For other web frame configurations and boundary conditions than those given in 4.6.2, a direct stress calculation shall be performed. The concentrated load on the web frame is given in The point of application is in each case to be chosen in relation to the arrangement of stringers and longitudinal frames so as to obtain the maximum shear and bending moments. Allowable stresses are as follows: Shear stress: Bending stress: τ = σ y 3 (4.14) σ = σ (4.15) b y Equivalent stress: σ = σ + 3τ = σ (4.16) c 2 2 b y 4.7 Bow Stem The stem shall be made of rolled, cast or forged steel or of shaped steel plates. A sharp edged stem (see Figure 4-4) improves the manoeuvrability of the ship in ice and is recommended particularly for smaller ships with a length under 150 m.

25 22 Figure 4-4. Example of a suitable stem The plate thickness of a shaped plate stem and in the case of a blunt bow, any part of the shell which forms an angle of 30 o or more to the centreline in a horizontal plane, shall be calculated according to the formula in assuming that: s is spacing of elements supporting the plate [m] p PL = p [MPa] (see 4.3.2) l a is spacing of vertical supporting elements [m] The stem and the part of a blunt bow defined above shall be supported by floors or brackets spaced not more than 0.6 m apart and having a thickness of at least half the plate thickness. The reinforcement of the stem shall extend from the keel to a point 0.75 m above UIWL or, in case an upper forward ice belt is required (4.3.1), to the upper limit of this Arrangements for towing A mooring pipe with an opening not less than 250 by 300 mm, a length of at least 150 mm and an inner surface radius of at least 100 mm shall be fitted in the bow bulwark at the centreline. A bitt or other means for securing a towline, dimensioned to stand the breaking force of the towline of the ship, shall be fitted. On ships with a displacement not exceeding 30,000 tons, the part of the bow which extends to a height of at least 5 metres above the UIWL and at least 3 metres back from the stem shall be strengthened to take the stresses caused by fork towing. For this purpose intermediate frames shall be fitted and the framing shall be supported by stringers or decks. It should be noted that fork towing is often the moste efficient way of assisting ships of moderate size (displacement not exceeding 30,000 tons) in ice. Ships with a bulb protruding more than 2.5 metres forward of the forward perpendicular are, however, often difficult to tow in this way. 4.8 Stern The introduction of new propulsion arrangements with azimuthing thrusters or podded propellers, which provide an improved manoeuvrability, will result in increased ice loading of the aft region and the stern area. This fact should be considered in the design of the aft/stern structure.

26 23 An extremely narrow clearance between the propeller blade tip and the stern frame shall be avoided as a small clearance would cause very high loads on the blade tip. On twin and triple screw ships the ice strengthening of the shell and framing shall be extended to the double bottom for 1.5 metres forward and aft of the side propellers. Shafting and stern tubes of side propellers shall normally be enclosed within plated bossings. If detached struts are used, their design, strength and attachments to the hull shall be duly considered. A wide transom stern extending below the UIWL will seriously impede the capability of the ship to back in ice, which is most essential. Therefore a transom stern shall not be extended below the UIWL, if this can be avoided. If unavoidable, the part of the transom below the UIWL shall be kept as narrow as possible. The part of a transom stern situated within the ice belt shall be strengthened as for the midship region. 4.9 Bilge keels Bilge keels are often damaged or ripped off in ice. The connection of bilge keels to the hull shall be so designed that the risk of damage to the hull, in case a bilge keel is ripped off, is minimized. To limit damage when a bilge keel is partly ripped off, it is recommended that bilge keels are cut up into several shorter independent lengths. 5 RUDDER AND STEERING ARRANGEMENTS The scantlings of rudder post, rudder stock, pintles, steering engine etc. as well as the capability of the steering engine shall be determined according to the rules of the Classification Society. The maximum service speed of the ship to be used in these calculations shall, however, not be taken as less than stated below: IA Super IA IB IC 20 knots 18 knots 16 knots 14 knots If the actual maximum service speed of the ship is higher, that speed shall be used. For the ice classes IA Super and IA the rudder stock and the upper edge of the rudder shall be protected against ice pressure by an ice knife or equivalent means. For the ice classes IA Super and IA due regard shall be paid to the excessive load caused by the rudder being forced out of the midship position when backing into an ice ridge. Relief valves for hydraulic pressure shall be effective. The components of the steering gear shall be dimensioned to stand the yield torque of the rudder stock. Where possible, rudder stoppers working on the blade or rudder head shall be fitted.

27 24 6 PROPULSION MACHINERY 6.1 Scope These regulations apply to propulsion machinery covering open- and ducted-type propellers with controllable pitch or fixed pitch design for the ice classes IA Super, IA, IB and IC. The given loads are the expected ice loads for the whole ship s service life under normal operational conditions, including loads resulting from the changing rotational direction of FP propellers. However, these loads do not cover off-design operational conditions, for example when a stopped propeller is dragged through ice. The regulations also apply to azimuthing and fixed thrusters for main propulsion, considering loads resulting from propeller-ice interaction. However, the load models of the regulations do not include propeller/ice interaction loads when ice enters the propeller of a turned azimuthing thruster from the side (radially) or load case when ice block hits on the propeller hub of a pulling propeller. Ice loads resulting from ice impacts on the body of thrusters have to be estimated, but ice load formulae are not available. 6.2 Symbols c m chord length of blade section c 0.7 m chord length of blade section at 0.7R propeller radius CP controllable pitch D m propeller diameter d m external diameter of propeller hub (at propeller plane) D limit m limit value for propeller diameter EAR expanded blade area ratio F kn maximum backward blade force for the ship s service life b F kn ultimate blade load resulting from blade loss through plastic bending ex F f kn maximum forward blade force for the ship s service life Fice kn ice load (Fice)max kn maximum ice load for the ship s service life FP fixed pitch h 0 m depth of the propeller centreline from lower ice waterline Hice m thickness of maximum design ice block entering to propeller I kgm 2 equivalent mass moment of inertia of all parts on engine side of component under consideration I t kgm 2 equivalent mass moment of inertia of the whole propulsion system k shape parameter for Weibull distribution LIWL m lower ice waterline m slope for SN curve in log/log scale M BL knm blade bending moment MCR maximum continuous rating n rev./s propeller rotational speed n n rev./s nominal propeller rotational speed at MCR in free running condition N reference number of impacts per propeller rotational speed per ice class class N total number of ice loads on propeller blade for the ship s service life ice N R reference number of load for equivalent fatigue stress (108 cycles)

28 N Q 25 number of propeller revolutions during a milling sequence P 0.7 m propeller pitch at 0.7R radius P 0.7n m propeller pitch at 0.7R radius at MCR in free running condition P 0.7b m propeller pitch at 0.7R radius at MCR in bollard condition Q knm Torque Q emax knm maximum engine torque Q max knm maximum torque on the propeller resulting from propeller-ice interaction Q motor knm electric motor peak torque Q n knm nominal torque at MCR in free running condition Qr knm maximum response torque along the propeller shaft line Q smax knm maximum spindle torque of the blade for the ship s service life R m propeller radius r m blade section radius T kn propeller thrust T kn maximum backward propeller ice thrust for the ship s service life b T kn maximum forward propeller ice thrust for the ship s service life f T n kn propeller thrust at MCR in free running condition Tr kn maximum response thrust along the shaft line t m maximum blade section thickness Z number of propeller blades α i [deg] duration of propeller blade/ice interaction expressed in rotation angle γ ε the reduction factor for fatigue; scatter and test specimen size effect γ ν the reduction factor for fatigue; variable amplitude loading effect γ m the reduction factor for fatigue; mean stress effect ρ a reduction factor for fatigue correlating the maximum stress amplitude to the equivalent fatigue stress for 10 8 stress cycles σ MPa proof yield strength of blade material 0.2 σ MPa mean fatigue strength of blade material at 10 8 cycles to failure in sea exp water σ MPa equivalent fatigue ice load stress amplitude for 10 8 stress cycles fat σ fl MPa characteristic fatigue strength for blade material σ MPa reference stress σ ref = 0.6 σ σ u ref σ MPa reference stress ref 2 σ ref 2 = 0. 7 σ u or σ ref 2 = 0.6 σ σ u whichever is less σ MPa maximum stress resulting from F st b or F f σ MPa ultimate tensile strength of blade material u ( ice ) bmax σ MPa principal stress caused by the maximum backward propeller ice load ( ice ) fmax σ MPa principal stress caused by the maximum forward propeller ice load ( σ ice ) max MPa maximum ice load stress amplitude

29 26 Table 6-1. Definition of loads F b F f Q smax T b T f Q max F ex Q r T r Definition The maximum lifetime backward force on a propeller blade resulting from propeller/ice interaction, including hydrodynamic loads on that blade. The direction of the force is perpendicular to 0.7R chord line. See Figure 6-1. The maximum lifetime forward force on a propeller blade resulting from propeller/ice interaction, including hydrodynamic loads on that blade. The direction of the force is perpendicular to 0.7R chord line. The maximum lifetime spindle torque on a propeller blade resulting from propeller/ice interaction, including hydrodynamic loads on that blade. The maximum lifetime thrust on propeller (all blades) resulting from propeller/ice interaction. The direction of the thrust is the propeller shaft direction and the force is opposite to the hydrodynamic thrust. The maximum lifetime thrust on propeller (all blades) resulting from propeller/ice interaction. The direction of the thrust is the propeller shaft direction acting in the direction of hydrodynamic thrust. The maximum ice-induced torque resulting from propeller/ice interaction on one propeller blade, including hydrodynamic loads on that blade. Ultimate blade load resulting from blade loss through plastic bending. The force that is needed to cause total failure of the blade so that plastic hinge is caused to the root area. The force is acting on 0.8R. Spindle arm is to be taken as 2/3 of the distance between the axis of blade rotation and leading/trailing edge (whichever is the greater) at the 0.8R radius. Maximum response torque along the propeller shaft line, taking into account the dynamic behavior of the shaft line for ice excitation (torsional vibration) and hydrodynamic mean torque on propeller. Maximum response thrust along shaft line, taking into account the dynamic behavior of the shaft line for ice excitation (axial vibration) and hydrodynamic mean thrust on propeller. Use of the load in design process Design force for strength calculation of the propeller blade. Design force for calculation of strength of the propeller blade. In designing the propeller strength, the spindle torque is automatically taken into account because the propeller load is acting on the blade as distributed pressure on the leading edge or tip area. Is used for estimation of the response thrust T r. T b can be used as an estimate of excitation for axial vibration calculations. However, axial vibration calculations are not required in the rules. Is used for estimation of the response thrust T r. T f can be used as an estimate of excitation for axial vibration calculations. However, axial vibration calculations are not required in the rules. Is used for estimation of the response torque (Q r ) along the propulsion shaft line and as excitation for torsional vibration calculations. Blade failure load is used to dimension the blade bolts, pitch control mechanism, propeller shaft, propeller shaft bearing and trust bearing. The objective is to guarantee that total propeller blade failure should not cause damage to other components. Design torque for propeller shaft line components. Design thrust for propeller shaft line components.

30 27 Shaft direction Back side F b Direction of rotation Figure 6-1. Direction of the backward blade force resultant taken perpendicular to chord line at radius 0.7R. Ice contact pressure at leading edge is shown with small arrows. 6.3 Design ice conditions In estimating the ice loads of the propeller for ice classes, different types of operation as given in Table 6-2 were taken into account. For the estimation of design ice loads, a maximum ice block size is determined. The maximum design ice block entering the propeller is a rectangular ice block with the dimensions H 2H 3H. The thickness of the ice block (Hice) is given in Table 6-3. Table 6-2. ice ice ice Ice class IA Super IA, IB, IC Operation of the ship Operation in ice channels and in level ice The ship may proceed by ramming Operation in ice channels Table 6-3. Thickness of the design maximum ice block entering the propeller (Hice) IA Super IA IB IC 1.75 m 1.5 m 1.2 m 1.0 m

31 Materials Materials exposed to sea water Materials of components exposed to sea water, such as propeller blades, propeller hubs, and thruster body, shall have an elongation of not less than 15 % on a test specimen, the gauge length of which is five times the diameter. A Charpy V impact test shall be carried out for materials other than bronze and austenitic steel. An average impact energy value of 20 J taken from three tests is to be obtained at minus 10 ºC Materials exposed to sea water temperature Materials exposed to sea water temperature shall be of ductile material. An average impact energy value of 20 J taken from three tests is to be obtained at minus 10 ºC. This requirement applies to blade bolts, CP mechanisms, shaft bolts, strut-pod connecting bolts etc. This does not apply to surface hardened components, such as bearings and gear teeth. 6.5 Design loads The given loads are intended for component strength calculations only and are total loads including ice-induced loads and hydrodynamic loads during propeller/ice interaction. The values of the parameters in the formulae in this section shall be given in the units shown in the symbol list. If the propeller is not fully submerged when the ship is in ballast condition, the propulsion system shall be designed according to ice class IA for ice classes IB and IC Design loads on propeller blades F b is the maximum force experienced during the lifetime of the ship that bends a propeller blade backwards when the propeller mills an ice block while rotating ahead. F f is the maximum force experienced during the lifetime of the ship that bends a propeller blade forwards when the propeller mills an ice block while rotating ahead. F b and F f originate from different propeller/ice interaction phenomena, not acting simultaneously. Hence they are to be applied to one blade separately Maximum backward blade force F b for open propellers [ ] EAR 2 Fb = 27 n D D [kn], when D Dlimit Z EAR 1.4 Fb = 23 [ n D] D Hice [kn], when D> D Z limit (6.1), (6.2) D limit H ice = [m]

32 29 n is the nominal rotational speed (at MCR in free running condition) for a CP propeller and 85% of the nominal rotational speed (at MCR in free running condition) for an FP propeller Maximum forward blade force F f for open propellers EAR 2 Ff = 250 D [kn], when D Dlimit Z EAR 1 Ff = 500 D Hice [kn], when D> D Z d 1 D limit (6.3) (6.4) D 2 = d 1 D limit H ice [m] Loaded area on the blade for open propellers Load cases 1-4 have to be covered, as given in Table 6-4 below, for CP and FP propellers. In order to obtain blade ice loads for a reversing propeller, load case 5 also has to be covered for FP propellers.

33 30 Table 6-4. Load cases for open propellers Force Loaded area Right-handed propeller blade seen from behind Load case 1 Fb Uniform pressure applied on the back of the blade (suction side) to an area from 0.6R to the tip and from the leading edge to 0.2 times the chord length. Load case 2 50% of Fb Uniform pressure applied on the back of the blade (suction side) on the propeller tip area outside 0.9R radius. Load case 3 Ff Uniform pressure applied on the blade face (pressure side) to an area from 0.6R to the tip and from the leading edge to 0.2 times the chord length. Load case 4 50% of Ff Uniform pressure applied on propeller face (pressure side) on the propeller tip area outside 0.9R radius. Load case 5 60% of Ff or Fb, whichever is greater Uniform pressure applied on propeller face (pressure side) to an area from 0.6R to the tip and from the trailing edge to 0.2 times the chord length

34 Maximum backward blade ice force F b for ducted propellers D [ ] EAR 2 Fb = 9.5 n D D [kn], when D D Z [ ] EAR ice Fb = 66 n D D H [kn], when D> D Z = 4 [m] limit H ice limit limit (6.5), (6.6) n is the nominal rotational speed (at MCR in free running condition) for a CP propeller and 85% of the nominal rotational speed (at MCR in free running condition) for an FP propeller Maximum forward blade ice force F f for ducted propellers EAR 2 Ff = 250 D [kn], when D Dlimit Z EAR 1 Ff = 500 D Hice [kn], when D> D Z d 1 D limit (6.7) (6.8) D 2 = d 1 D limit H ice [m] Loaded area on the blade for ducted propellers Load cases 1 and 3 have to be covered as given in Table 6-5 for all propellers, and an additional load case (load case 5) for an FP propeller, to cover ice loads when the propeller is reversed.

35 32 Table 6-5. Load cases for ducted propellers Force Loaded area Right handed propeller blade seen from behind Load case 1 Fb Uniform pressure applied on the back of the blade (suction side) to an area from 0.6R to the tip and from the leading edge to 0.2 times the chord length. Load case 3 Ff Uniform pressure applied on the blade face (pressure side) to an area from 0.6R to the tip and from the leading edge to 0.5 times the chord length. Load case 5 60% of Ff or Fb, whichever is greater Uniform pressure applied on propeller face (pressure side) to an area from 0.6R to the tip and from the trailing edge to 0.2 times the chord length Maximum blade spindle torque Q smax for open and ducted propellers The spindle torque Q smax around the axis of the blade fitting shall be determined both for the maximum backward blade force F b and forward blade force F f, which are applied as in Table 6-4 and Table 6-5. If the above method gives a value which is less than the default value given by the formula below, the default value shall be used. Default value Q = 0.25 F c [knm] (6.9) smax 0.7 c 0. 7 is the length of the blade section at 0.7R radius and F is either F b or F f, whichever has the greater absolute value Load distributions for blade loads The Weibull-type distribution (probability that F ice exceeds (F ice ) max ), as given in Figure 6-2, is used for the fatigue design of the blade. P F ice ( F ) ( F ) ice max F = e ice max k F ln ice max ( F ) ice ( N ) (6.10)