Section 6 Mooring arrangements

6.1.1 Ships of Rule length L_R less than 90 m are recommended to have mooring lines as specified in Vol 1, Pt 3, Ch 5, 6.2 Mooring lines (Equipment Number ≤ 2000) or Vol 1, Pt 3, Ch 5, 6.3 Mooring lines (Equipment Number > 2000) as appropriate.

6.1.2 Ships of Rule length L_R 90 m or more are recommended to have mooring lines as specified in Vol 1, Pt 3, Ch 5, 6.2 Mooring lines (Equipment Number ≤ 2000) or Vol 1, Pt 3, Ch 5, 6.3 Mooring lines (Equipment Number > 2000) as appropriate.

6.1.3 It is recommended that not less than four mooring lines be carried on ships exceeding 90 m in length, and not less than six mooring lines on ships exceeding 180 m in length. The length of mooring lines should be not less than 200 m, or the length of the ship, whichever is the lesser.

6.1.4 For ease of handling, fibre ropes should be not less than 20 mm diameter. All ropes having breaking strengths in excess of 736,0 kN and used in normal mooring operations are to be handled by, and stored on, suitably designed winches. Alternative methods of storing should give due consideration to the difficulties experienced in manually handling ropes having breaking strengths in excess of 490,0 kN

6.1.5 It is permitted to reduce the specified length of an individual mooring line by up to 7 per cent, provided the total length of mooring lines is not less than the total length if all the required lines were of equal given lengths. Proposals to fit individual mooring lines of reduced length to suit the particular service will be specially considered.

6.1.6 Ship Design Minimum Breaking Load (MBL_SD) is the minimum breaking load of new, dry mooring lines for which shipboard fittings and supporting hull structures are designed in order to meet mooring restraint requirements.

6.1.7 Line Design Break Force (LDBF) is the minimum force at which a new, dry, spliced, mooring line will break at. This is applicable to all synthetic cordage materials.

6.2.1 It is recommended that the ship design minimum breaking load, length and number of mooring lines provided on board ships with equipment number of less than or equal to 2000 be not less than those specified in Table 5.6.1 Equipment - Kedge anchors and wires, towlines and mooring lines. The equipment number is to be calculated in accordance with Vol 1, Pt 3, Ch 5, 2.1 Equipment Number calculation. It is the Owner and designer's responsibility to ensure the adequacy of the mooring equipment. The adequacy of minimum recommended mooring lines in this sub-s ection needs to be verified based on assessments carried out for the individual mooring arrangement, expected shore-side mooring facilities and design environmental conditions for the berth.

6.2.3 As an alternative to the minimum recommendations for mooring lines prescribed in this sub-section, the minimum recommendations for mooring lines may be determined by direct mooring analysis in accordance with the procedure given in Appendix A of IACS Recommendation 10 Chain Anchoring, Mooring and Towing Equipment.

6.3.4 The maximum wind speed V_w is representative of the mean wind speed over a 30 second period from any direction and at a height of 10 m above the ground. The current speed considered is a representative of the maximum current speed acting on bow or stern (±10°) at a depth of one-half of the mean draught. Furthermore, it is considered that the ships are moored to solid piers that provide shielding against cross currents.

6.3.5 Additional loads caused by higher wind or current speeds, cross currents, additional wave loads, or reduced shielding from non-solid piers, for example are to be specially considered. Consideration is also to be given to the fact that unfavourable mooring layouts can significantly increase the loads on individual mooring lines.

Figure 5.6.1 Typical mooring arrangement

6.3.9 The total number of head, stern and breast lines is specified as:

n

=

where

A1

=

side projected area as defined by Vol 1, Pt 3, Ch 5, 6.3 Mooring lines (Equipment Number > 2000) 6.3.2

The total number of head, stern and breast lines is to be rounded to the nearest whole number. The number may be increased or decreased in conjunction with an adjustment to the ship design minimum breaking load. The adjusted ship design minimum breaking load , is to be taken as:

	=
	=

where

MBLSD	=	MBLSD or , if intended ship design minimum breaking load is different as provided by Vol 1, Pt 3, Ch 5, 6.3 Mooring lines (Equipment Number > 2000) 6.3.7 or Vol 1, Pt 3, Ch 5, 6.3 Mooring lines (Equipment Number > 2000) 6.3.8
n	=	number of lines for the considered ship type as calculated by the above formula without rounding
n**	=	increased or decreased total number of head, stern and breast lines

Vice versa, the ship design minimum breaking load of head, stern and breast lines may be increased or decreased in conjunction with an adjustment to the number of lines.

6.3.11 As an alternative to the minimum recommendations for mooring lines prescribed in this sub-section, the minimum recommendations for mooring lines may be determined by direct mooring analysis in accordance with the procedure given in Appendix A of IACS Recommendation 10 ‘Chain Anchoring, Mooring and Towing Equipment’.

6.4.1 Mooring lines may be of steel wire rope, natural fibre or synthetic fibre. The diameter, construction and specification of wire or natural fibre mooring lines are to comply with the requirements of Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials. Where it is proposed to use synthetic fibre ropes, the size and construction will be specially considered.

6.4.2 The design loads applied to deck fittings by Vol 1, Pt 3, Ch 5, 6.9 Deck fittings and support structure relate to conventional fibre ropes (i.e. polypropylene, polyester and nylon). If other materials are used i.e. HMPE, consideration should be given to the elongation properties and therefore the design load applied to deck fittings.

6.4.3 Wire rope mooring lines used in association with winches (on which the rope is stored on the winch drum) are to be of suitable construction.

6.5.1 Mooring ropes are to be tested and certified in accordance with Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials.

6.6.1 Means are to be provided to enable mooring lines to be adequately secured on board ship.

6.6.2 It is recommended that the total number of suitably placed bollards on either side of the ship and/or the total brake holding power of mooring winches should be capable of holding not less than 1,5 times the sum of the ship design minimum breaking load (MBL_SD) of the mooring lines recommended.

6.7.1 The recommendations with respect to the mooring arrangement and mooring winches are provided by this sub-Section.

6.7.2 Mooring lines in the same service (e.g. breast lines) are to be of the same characteristics in terms of strength and elasticity.

6.7.3 Mooring winches where provided are to be suitable for the intended purpose. As far as possible, a sufficient number of mooring winches is to be fitted so as to allow all mooring lines to be belayed on winches. This allows for an efficient distribution of the load to all mooring lines in the same service and for the mooring lines to shed the load before they break. If the mooring arrangement is designed such that mooring lines are partly to be belayed on bitts or bollards, it is to be understood that these lines may not be as effective as the mooring lines belayed on winches.

6.7.4 The mooring winch is to be fitted with brakes, the holding capacity of which is sufficient to prevent unreeling of the mooring line when the rope tension is equal to 80 per cent of the ship design minimum breaking load of the rope as fitted on the first layer. The winch is to be fitted with brakes that will allow for the reliable setting of the brake rendering load.

6.7.5 For powered winches the maximum hauling tension which can be applied to the mooring line (the reeled first layer) is to be not less than 2/9, nor to be more than, 1/3, of the rope's ship design minimum breaking load. For automatic winches these figures apply when the winch is set to the maximum power with automatic control.

6.7.6 For powered winches on automatic control, the rendering tension which the winch can exert on the mooring line (the reeled first layer) is not to exceed 1,5 times, nor be less than 1,05 times, the hauling tension for that particular power setting of the winch. The winch is to be marked with the range of rope strengths for which it is designed.

6.7.7 Mooring lines are to have a straight lead from the mooring drum to the fairlead as far as practicable.

6.7.8 When a mooring line changes direction, the contact surface on the fitting shall have a large radius so as to minimise the wear experienced by the mooring lines. Recommendations from the rope manufacturer for the intended rope type are also to be complied with.

6.8.1 Mooring lines are to be of wire, natural fibre or synthetic fibre construction or of a mixture of wire and fibre. For synthetic fibre ropes it is recommended that lines with reduced risk of recoil (snap-back) be used to mitigate the risk of injuries or fatalities in the case mooring line failure.

6.8.2 Notwithstanding the strength recommendations, no fibre rope shall be less than 20 mm in diameter. For polyamide ropes the line design break force is to be increased by 20 per cent and for other synthetic ropes by 10 per cent to account for strength loss due to, among other causes, aging and wear.

6.8.3 Wire ropes used for mooring lines are generally to be of a flexible construction with not less than 144 wires in six strands with seven fibre cores for strengths up to 490 kN, and 222 wires in six strands with one fibre core for strengths exceeding 490 kN. The wires laid round the fibre centre of each strand are to be made up in not less than two layers.

6.8.4 Wire ropes for mooring lines used in association with mooring winches (on which the rope is stored on the winch drum) are to be of suitable construction.

6.8.5 The mooring lines are to be tested in accordance with Ch 10, 6 Steel wire ropes and Ch 10, 7 Fibre ropes of the Rules for the Manufacture, Testing and Certification of Materials, July 2022 for wire ropes and fibre ropes, respectively.

6.9.1 The strength of shipboard fittings used for mooring operations and their supporting hull structures as well as the strength of supporting hull structures of winches and capstans are to comply with the requirements specified in this sub-Section.

6.9.2 Shipboard fittings, winches and capstans for mooring are to be located on stiffeners and/or girders which are part of the deck construction so as to facilitate efficient distribution of the mooring load. Other arrangements are acceptable (for chocks in bulwarks, etc.) provided that the strength is confirmed adequate for the service.

6.9.3 The design load applied to shipboard fittings and supporting hull structure is not to be less than that given in Table 5.6.2 Minimum design load for deck fittings and supporting structure - Mooring.

6.9.4 The design load is to be applied to fittings in all directions that may occur by taking into account the arrangement shown on the towing and mooring arrangements plan. Where the mooring line takes a turn at a fitting the total design load applied to the fitting is equal to the resultant of the design loads acting on the line, see Figure 5.6.2 Design load applied to fittings. However, in no case does the design load applied to the fitting need to be greater than twice the design load on the line.

Figure 5.6.2 Design load applied to fittings

6.9.5 Shipboard fittings are to be selected from an acceptable National or International standard and to be based on the ship design minimum breaking load as given in Vol 1, Pt 3, Ch 5, 6.1 Mooring lines 6.1.1 or Vol 1, Pt 3, Ch 5, 6.1 Mooring lines 6.1.2 as appropriate (see Note 2 of Table 5.6.2 Minimum design load for deck fittings and supporting structure - Mooring).

6.9.6 Mooring bitts (double bollards) are to be chosen for the mooring line attached in figure-of-eight fashion if the industry standard distinguishes between different methods to attach the line, i.e. figure-of-eight or eye-splice attachment. With the line attached to a mooring bitt in the usual way (figure-of-eight fashion), either of the two posts of the mooring bitt can be subjected to a force twice as large as that acting on the mooring line. Disregarding this effect, depending on the applied industry standard and fitting size, overload may occur.

6.9.7 When the shipboard fitting is not selected from an accepted industry standard, the strength of the fitting based on net scantlings and its attachment to the ship is to be adequate for the loads specified in Table 5.6.2 Minimum design load for deck fittings and supporting structure - Mooring based on the acceptance criteria given Vol 1, Pt 3, Ch 5, 6.9 Deck fittings and support structure 6.9.10 or Vol 1, Pt 3, Ch 5, 6.9 Deck fittings and support structure 6.9.11 as appropriate. Mooring bitts (double bollards) are required to resist the loads caused by the mooring line attached in figure-of-eight fashion. For strength assessment, beam theory or finite element analysis using net scantlings is to be applied, as appropriate. Wear down allowance for shipboard fittings not selected from an accepted industry standard is not to be less than 1,0 mm, added to surfaces which are intended to regularly contact the line.

6.9.8 The net scantlings of the supporting hull structure for the fittings are to be adequate for the loads given in Table 5.6.2 Minimum design load for deck fittings and supporting structure - Mooring based on the acceptance criteria given in Vol 1, Pt 3, Ch 5, 6.9 Deck fittings and support structure 6.9.10 or Vol 1, Pt 3, Ch 5, 6.9 Deck fittings and support structure 6.9.11 as appropriate. The arrangement of reinforced members beneath shipboard fittings, winches and capstans is to consider any variation of direction (horizontally and vertically) of the mooring forces acting upon the shipboard fittings, see Figure 5.6.3 Supporting hull structure for a sample arrangement. Proper alignment of fitting and supporting hull structure is to be ensured. The acting point of the mooring force on a shipboard fitting is to be taken at the attachment point of a mooring line or at a change in its direction.

6.9.9 For bollards and bitts the attachment point of the mooring line is to be taken not less than 4/5 of the tube height above the base, see Figure 5.6.3 Supporting hull structure. However, if fins are fitted to the bollard tubes to keep the mooring line as low as possible, then the attachment point of the mooring line is to be taken at the location of the fins, see Figure 5.6.3 Supporting hull structure.

Figure 5.6.3 Supporting hull structure

6.9.10 In the case of strength assessment using beam theory or grillage analysis, the stress within the supporting structure of fittings, with net scantlings, is not to exceed that given in Table 5.6.3 Allowable stress within the supporting structure of shipboard fittings.

6.9.11 For strength assessment by means of finite element analysis the mesh is to be fine enough to represent the geometry as realistically as possible. The aspect ratios of elements are not to exceed three. Girders are to be modelled using shell or plane stress elements. Symmetric girder flanges may be modelled by beam or truss elements. The element height of girder webs must not exceed one-third of the web height. In way of small openings in girder webs the web thickness is to be reduced to an appropriate mean thickness over the web height. Large openings are to be modelled. Stiffeners may be modelled using shell or plane stress elements. The mesh size of stiffeners is to be fine enough to obtain proper bending stress. If flat bars are modelled using shell or plane stress elements, then dummy rod elements are to be modelled at the free edge of the flat bars and the stresses of the dummy elements are to be evaluated. Stresses are to be read from the centre of the individual element. For shell elements the stresses are to be evaluated at the mid plane of the element. The Von Mises stress within the supporting structure of fittings, calculated with net scantlings, is not to exceed the specified minimum yield strength of the material.

6.9.12 The Safe Working Load (SWL) is the safe load limit of shipboard fittings used for mooring purposes. Unless a greater SWL is requested, the SWL assigned shall be the ship design minimum breaking load given in Vol 1, Pt 3, Ch 5, 6.1 Mooring lines 6.1.1 or Vol 1, Pt 3, Ch 5, 6.1 Mooring lines 6.1.2, (see Note 2 of Table 5.6.2 Minimum design load for deck fittings and supporting structure - Mooring).

6.9.13 The SWL, in tonnes, of each shipboard fitting is to be marked (by weld bead or equivalent) on the deck fittings used for mooring.

6.9.14 The above requirements on SWL apply for the use with no more than one mooring line.

6.9.15 The mooring arrangements plan as mentioned in Vol 1, Pt 3, Ch 5, 6.10 Mooring arrangements plan is to define the method of use of mooring lines.

Table 5.6.3 Allowable stress within the supporting structure of shipboard fittings

	Normal stress, in N/mm2	Shear stress, in N/mm2
Allowable stress
where σ0 = specified minimum yield strength of the material in N/mm2 Note Normal stress is defined as the sum of bending and axial stresses. No stress concentration factors accounted for and as such may need to be considered separately.

6.10.1 The SWL for the intended use for each shipboard fitting is to be noted in the mooring arrangements plan available on board for the guidance of the Master.

6.10.3 The above information as given in Vol 1, Pt 3, Ch 5, 6.10 Mooring arrangements plan 6.10.2 is to be incorporated into the pilot card in order to provide the pilot proper information on harbour and other towing operations.