Section 9 Fibre ropes
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 3 Functional Unit Types and Special Features - Chapter 10 Positional Mooring Systems - Section 9 Fibre ropes

Section 9 Fibre ropes

Parent topic: Chapter 10 Positional Mooring Systems

9.1 General

9.1.1 This Section gives requirements for fibre ropes part of loose or semi-taut catenary mooring lines of positional mooring systems of offshore units.

The use of fibre rope is confined to the suspended immersed part of the catenary system.

Generally chain or wire rope or special connectors shall be fitted in parts of the anchor leg subject to contact with sea bed or in the vicinity of the attachment point of the mooring line to the offshore unit.

Note that the requirements Pt 3, Ch 13, 5 Mooring hawsers and load monitoring, only apply to hawsers used in temporary berthing of shuttle tankers or ship to CALM buoys operated, inspected and maintained in accordance with OCIMF recommendations. Fibre ropes used as hawsers in the long term mooring of Offshore Units to CALM buoy or SALM system shall generally comply with the requirements of this Pt 3, Ch 10 Positional Mooring Systems and specific requirements on fibre ropes from this section. They shall be designed for the site specific loading (strength and fatigue) with sufficient redundancy (i.e. considering one line failed case).

9.1.2 Acceptance of fibre ropes will be based on:

  • submission of complete design, manufacturing and installation documentations for design appraisal by LR.
  • compliance with API RP 2SM Design, Manufacture, Installation, and Maintenance of Synthetic Fibre Ropes for Offshore Mooring as applicable to the specific rope design, field deployment and service.
  • compliance with the requirements of this section and the requirement of LR Rules for Materials (especially Ch 10 Equipment for Mooring and Anchoring) where this is more specific or onerous as applicable to the specific rope design, field deployment and service.
  • qualification testing as agreed with LR (and generally in line with API RP 2SM).
  • manufacturing and production testing under LR Survey and certification by LR.

9.2 Design aspects

9.2.1 Fibre ropes and associated fittings are to be of an approved design. The following information to be submitted:
  1. Specifications:
    • Rope purchaser’s functional and manufacturing specifications.
    • Rope design specification.
    • Rope manufacturing and testing specification.
  2. Plans:
    • Rope assembly, spool piece and other fittings (pins, shackles, connectors etc.).
  3. Calculations:
    • Strength and fatigue of rope and fittings.
  4. Rope particulars:
    • Fibre type.
    • Diameter of rope.
    • Length at specified reference tension.
    • Construction.
    • Weight in air and water.
    • Sheath or jacket type and characteristics.
    • Terminations.
    • Bend limiters.
  5. Rope properties:
    • Minimum breaking strength.
    • Mean breaking load of rope and coefficient of variation, from tests.
    • Axial stiffness values (to cover upper and lower bounds of stiffness).
    • Fatigue data (tension-tension and compression).
    • Creep.
    • Hysteresis.
    • Torque/twist.
    • Resistance to chemical attack in an offshore environment.
    • Long-term degradation.
    • Inspection, maintenance and repair plan.

9.2.2 Factors of safety for fibre rope are to be a minimum of 20 per cent higher than the levels given in Pt 3, Ch 10, 6 Anchor lines for chain and wire rope materials.

Factor of safety =

A reduction factor will require to be applied to the standard designated Minimum Breaking Strength, where the test database for the rope type is statistically small.

This does not generally apply to polyester fibre ropes for which sufficient test data, manufacturing and service experience can be documented.

9.2.3 Fibre ropes shall remain within the water column under all service conditions and not touch the sea bed in any intact or damaged condition.

9.2.4 Fibre ropes shall be kept sufficiently far below the waterline, and below the connection point on the unit, to avoid any possibility of contact damage, degradation by UV exposure, excessive marine growth developing on the sheathing, detrimental intermittent soaking/drying etc.

9.3 Manufacture

9.3.1 Fibre ropes are to be manufactured at a works approved by LR.

9.3.2 Ropes and fittings will be subject to LR survey during manufacture and testing.

9.3.3 A certified ISO 9001/9002 Quality System is to be in place and a quality plan is to be produced and agreed with LR Surveyors.

9.3.4 The ropes and fittings are to be manufactured in accordance with the approved design, standards and procedures.

9.3.5  See also requirement of Ch 10, 7 Fibre ropes of the Rules for Materials.

9.4 Additional specific requirements

9.4.1 The purchaser is to specify the project specific material, manufacturing and testing requirements where these complement, exceed or are more onerous than those of this Pt 3, Ch 10, 9 Fibre ropes , Ch 10 Equipment for Mooring and Anchoring of the Rules for Materials (e.g. chain length and tolerances, maximum yield strength, coating, reference link identification etc.) or API RP 2SM. These shall be reported and agreed with LR.

9.4.2 A datasheet is to summarise all characteristics of each fibre rope segment as necessary to ensure satisfactory deployment of the rope within the Positional Mooring System and to support the in service inspection, repair and maintenance plan.

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.