ABS updates Requirements for Position Mooring Systems

The American Bureau of Shipping has updated its Requirements for Position Mooring Systems.

These Requirements were published on February 1st, 2023, and entered into force on the same date.

This document provides criteria, technical requirements, and guidance on the design and analysis of position mooring systems.

It supplements the following ABS Rules for issuing classification notations relevant to position mooring systems:

ABS Rules for Building and Classing Floating Production Installations (FPI Rules)
ABS Rules for Building and Classing Mobile Offshore Units (MOU Rules)
ABS Rules for Building and Classing Single Point Moorings (SPM Rules)
ABS Guide for Building and Classing Floating Offshore Liquefied Gas Terminals (FLGT Guide)
ABS Rules for Building and Classing Marine Vessels (Marine Vessel Rules)

In addition to the consolidation of the current requirements, this document also includes updates in the following areas based on the latest industry knowledge and experiences:

Vortex Induced Motion (VIM) effect (8/3.7, 8/5.13)
Bending-tension fatigue of mooring chains (3/7.5)
Fiber rope mooring criteria (3/7.3)
Mooring systems in squalls (3/3.5, 8/3.1, 8/5.11)
Dynamically installed anchors (3/7.9, 6/5.7)
Anchor holding capacity (6/5.7)
Mooring analysis methodology (Section 8)
Thruster-Assisted Mooring (Section 4)

The figure below shows the relationship between this document and other ABS Rules/Guides/Guidance Notes.

This document focuses on design aspect of position mooring systems. Survey requirements remain in relevant Rules/Guides and are referenced in this document.

The design requirements for position mooring systems will be removed from above mentioned Rules/Guides and replaced with references to this document on 1 July 2019.

Before 1 July 2019, designers could choose to use this document or applicable Rules/Guides mentioned above.

On 1 July 2019, the AM Guide and Pre-Laid Guide were withdrawn and only this document remains for the design of position mooring system.

The May 2020 version clarified the requirements for out-of-plane bending analysis in 3/7.5.3 and added requirements for wave-current interaction effects on wave drift force in 8/3.9.2.

The April 2022 version updated the fatigue factor of safety in Section 3, Table 4 to account for out-ofplane bending, in-plane bending, and tension-tension analysis and added a new Subsection 3/11 on temporary operation of mooring systems.

The February 2023 version specifies that Kenter links, pear links, and other temporary mooring connectors are not to be used in permanent mooring systems and provides requirements for connectors to be used in permanent mooring applications.

Users are advised to check periodically on the ABS website www.eagle.org to verify that this version is the most current.