MEG4
What is LDBF in MEG4?
6 min read
LDBF is the term that replaced casual use of 'breaking strength' in modern mooring practice. If you are buying a mooring line today, this is the number the conversation should be built around.
Definition
LDBF stands for line design break force: the minimum break force a new, dry, spliced mooring line is designed to achieve. The key words are new, spliced and minimum.
It is not the average break load of a batch, and it is not the strength of an unspliced sample of rope. A spliced eye is part of the line, and splicing reduces strength relative to the bare rope, so quoting the bare rope figure overstates what the line can actually do in service.
Why the industry moved to it
Historically, ropes were quoted on minimum break load or on average break load, and different manufacturers used the terms differently. Two lines with the same headline number could behave very differently on deck. MEG4 pushed the industry towards a single defined design figure so that a line could be selected against the ship's own design figure rather than against a marketing number.
The practical result: when you compare two offers, compare LDBF for a spliced line, not one manufacturer's average break load against another's minimum.
How LDBF relates to the ship design MBL
The ship design MBL is a property of the vessel — it comes from the mooring system design and is fixed in the ship's documentation. LDBF is a property of the rope you buy.
Under MEG4 guidance, the LDBF of a new mooring line is normally selected within a band of the ship design MBL, typically in the region of 100 to 105 percent. The reason for the narrow band is that the mooring line is intended to be the weakest, sacrificial element in the system: if something has to fail, it should be the rope, not the bitt, the fairlead or the winch foundation.
This is the single most misunderstood point in mooring purchasing. A stronger rope is not a safer rope. Over-specifying LDBF moves the failure point into the ship's structure.
What this means when you order
- Ask for LDBF, spliced, for the exact construction and diameter offered
- Give the supplier your ship design MBL rather than asking for 'the strongest rope you have'
- Check that the offered LDBF sits in the band your mooring management plan specifies
- Confirm the certificate states the tested figure and the test standard used
Terminology you will see alongside it
| Term | Meaning |
|---|---|
| Ship design MBL | The design minimum breaking load of the ship's mooring system |
| LDBF | Line design break force — the new spliced line's design break force |
| WLL | Working load limit of a fitting or item of equipment |
| LMP | Line management plan — how lines are tracked, inspected and retired |
| MSMP | Mooring system management plan — the overall vessel mooring documentation |
Frequently Asked Questions
- Not exactly. LDBF is defined for a new, dry, spliced line, which is what actually goes into service. Bare-rope minimum breaking load figures are usually higher because they exclude the strength loss at the splice.
Need this applied to your vessel?
Send us the ship design MBL, the required diameter, construction and length, the delivery port and the date. We will come back with a line configuration and the documentation it will carry.
Request a quotation