Beginnings of a Unified Approach to Mooring Design: Working Load Limits' Literature Review & Observations

Abstract

Design considerations for mooring of ships to piers and wharves often include a Working Load Limit (WLL) on mooring lines expressed as a percentage of their Minimum Breaking Load (MBL). Commonly specified limits include 55% MBL for wires, 45% MBL for polyamide or nylon lines, and 50% MBL for other synthetic lines, whose origins can be traced back to British Ship Research Association reports published from 1967 to 1973. Literature research indicates that a recurrent historical adoption of early recommendations on WLLs appears to have been the mechanism through which modern standards have been developed, and it's unclear whether the origin and intended application of these limits have been re-examined as revised versions of older guidelines have been put forward. These limits remain useful and of significant relevance in the industry, to the degree that they are commonplace and provide a safety-factor approach to prevent the overloading of mooring lines. This paper presents the history of the WLLs so that their original purpose can be re-evaluated, maintained or modified in the development of unified mooring design guidelines that better suit modern engineering practice.