Section 7 Mooring ropes and towlines
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 3 General Requirements and Constructional Arrangements - Chapter 5 Anchoring and Mooring Equipment - Section 7 Mooring ropes and towlines

Section 7 Mooring ropes and towlines

Parent topic: Chapter 5 Anchoring and Mooring Equipment

7.1 Mooring ropes

7.1.1 It is the Owner and designer's responsibility to ensure the adequacy of the mooring equipment including mooring ropes. The Table 5.7.1 Towlines and mooring lines provides minimum recommendations. 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.

7.1.2 The lengths of individual mooring lines in Table 5.7.1 Towlines and mooring lines may be reduced by up to seven per cent of the Table length, provided that the total length of mooring lines is not less than would have resulted had all lines been of equal length. Proposals to fit individual mooring lines of reduced length to suit the particular service will be specially considered.

7.2 Materials

7.2.1 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 Anchoringof the Rules for Materials . Where it is proposed to use synthetic fibre ropes, the size and construction will be specially considered.

7.3 Testing and certification

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

7.4 Towlines

7.4.1 Towlines are not required for classification other than for craft which are required to comply with the IMO Code of Safety for High Speed Craft. The details given in Table 5.7.1 Towlines and mooring lines are for guidance purposes only.

Table 5.7.1 Towlines and mooring lines

Equipment
Number 		Towline,
See Notes 		Mooring lines
Exceeding Not Exceeding Minimum length, in metres Minimum breaking strength, in kN Number of lines Minimum length of each line, in metres Minimum breaking strength, in kN
- 5 90 19,9 2 55 13,9
5 10 90 22,5 2 55 17,6
10 15 90 27,7 2 55 21,5
15 20 90 32,9 2 55 24,5
             
20 25 110 38,1 2 55 26,6
25 30 110 43,3 2 55 28,2
30 35 110 48,5 2 55 29,6
             
35 40 135 53,7 2 55 30,8
40 45 135 58,9 2 70 31,8
45 50 135 64,1 2 85 32,7
             
50 70 180 71,0 2 100 35,5
70 90 180 82,1 2 100 39,3
90 110 180 93,2 2 110 43,1
             
110 130 180 104,3 2 110 46,6
130 150 180 115,3 2 120 50,2
150 175 180 127,8 2 120 54,4
             
175 205 180 143,0 2 120 58,8
205 240 180 161,1 2 120 64,2
240 280 180 181,8 3 120 71,1
             
280 320 180 204,0 3 140 78,5
320 360 180 226,1 3 140 85,8
360 400 180 248,3 3 140 93,2
             
400 450 180 273,2 3 140 100,5
450 500 180 300,9 3 140 107,9
500 550 180 328,6 4 160 112,8
             
550 600 180 356,3 4 160 117,7
600 660 180 386,8 4 160 122,6
660 720 180 420,1 4 160 127,5
             
720 780 180 453,3 4 170 132,4
750 840 180 486,5 4 170 137,3
840 910 180 522,5 4 170 142,2
             
910 980 180 561,3 4 170 147,1
980 1060 180 602,9 4 180 156,9
1060 1140 180 647,2 4 180 166,7

Note 1. Towline specified for guidance only, see Pt 3, Ch 5, 7.4 Towlines 7.4.1.

Note 2. Wire ropes used for towlines and 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
222 wires in six strands with one fibre core for strenghths exceeding 490 kN
The wires to be laid around the fibre centre of each strand are to be up in not less than two layers.

Note 3. Wire ropes for towlines and mooring lines used in association with mooring winches (on which the rope is stored on the winch drum) are to be of suitable construction.

Note 4. Irrespective of strength of requirements, no fibre rope is to be less than 12 mm diameter.

7.5 Bollards, fairleads and bull rings

7.5.1 Means are to provided to enable mooring lines to be adequately secured on board the craft. It is recommended that the total number of suitably placed bollards on either side of the craft 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 maximum breaking strengths of the mooring lines required or recommended. Attention is drawn to the existence of a number of National Standards for bollards and fairleads, and to the importance of ensuring that their seating arrangements, including the supporting hull structure, are efficiently constructed and adequate for the intended loads.

7.6 Towing requirements

7.6.1 Craft which are to comply with the IMO Code of Safety for High Speed Craft are to be provided with adequate arrangements to enable the craft to be towed in the worst intended environmental conditions. It is recommended that other craft comply with this requirement.

7.7 Towing bitts

7.7.1 Where towage is to be from more than one point a suitable bridle is to be provided.

7.7.2 Details of the structural scantlings, arrangements, loadings and design assumptions for the towing bitts are to be submitted for consideration.

7.7.3 The towing arrangements should be such that damage to the towline or bridle from abrasion is minimised.

7.8 Mooring winches

7.8.1 Mooring winches where provided are to be suitable for the intended purpose. Supports under the winches are to be to the Surveyor's satisfaction.

7.8.2 Mooring winches are to be fitted with drum brakes, the strength of which is sufficient to prevent unreeling of the mooring line when the rope tension is equal to 80 per cent of the breaking strength of the rope as fitted on the first layer on the winch drum, see also Pt 3, Ch 5, 7.5 Bollards, fairleads and bull rings 7.5.1.

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.