Ship Design Minimum Breaking Load
MBL_SD and the OCIMF MEG4 strength ladder: line and tail design break force, the working load limit, the brake render setting and the retirement threshold.
The ship design minimum breaking load is the breaking load of new, dry mooring lines for which a ship’s mooring system is designed, established so the system meets the OCIMF standard environmental criteria restraint requirements. Every other strength figure in a modern mooring arrangement is expressed as a percentage of it.
The full article will carry the ladder that OCIMF MEG4 built on that single reference: line design break force at 100 to 105 percent of it, tail design break force at 125 to 130 percent, working load limit at 55 percent for steel wire rope and 50 percent for other cordage, winch brake render setting at 60 percent, and line retirement when residual strength falls to 75 percent. It will explain why the band on line design break force has an upper limit as well as a lower one, so that an over-strong replacement line does not defeat the designed failure sequence.
MEG4 deliberately retired the bare term minimum breaking load as a design reference because it invited readers to apply percentages to whatever line happened to be fitted rather than to the value the ship was designed around. That distinction is the reason this term exists and it is still widely mis-stated.