Terminology can be confusing and common terms that are used across industry can mean different things to different groups. In the years since the Mooring Equipment Guidelines, Third Edition (MEG3) was published, there has been a misunderstanding of mooring lin720e strength terminology. One example is Minimum Breaking Load (MBL).
In MEG3, OCIMF defined MBL as "the minimum breaking load of a new dry mooring line or chain as declared by the manufacturer". But industry has also used MBL to mean test and calculation methods for mooring line break force. This has led to confusion between line users and manufacturers, and to differences between expected and actual mooring line performance. Eg. Similar mooring lines may in the past, have had a variation in tested break force of =/- 10%. Some Operators have purchased stronger ropes and adjusted winch brake setting to the increased rope MBL, thus reducing the safety factor between the line and winch.
Due to the use of the term Minimum Breaking Load, many mooring line users have come to the misunderstanding that lines can be safely loaded up to their MBL with no failures or degradation. This is not the case and OCIMF wants to make sure people understand the importance of safety margins on mooring lines. There is also confusion among some ship owners who incorrectly believe that mooring line certificates must exactly match the MBL requested.
To resolve this confusion, OCIMF has collaborated closely with the Cordage Institute, Eurocord, International Association of Classification Societies and Ship builders association to clearly define a set of terms and test methods for mooring line MBL that can be used consistently by both line users and manufacturers when designing, specifying, testing and operating mooring lines. These new terms will align the cordage and the tanker industries to a common language.
MBL Ship Design MBL
Line Design Break Force (LDBF)
Working Load Limit (WLL)
Figure 1.3 (page 8-9) and 1.4 (page 10) illustrates the relationship between strengths of mooring system components as per new terminology introduced in MEG4.