Industry practice has not been consist.ent in this respect. Some designers base the strength of fillings
and equipment on the maximum line tension anticipated for certain weather criteria.; others base the
breaking strength of fill ings and equipment on the minimum breaking load of mooring line. Neither
of these strengIh criteria is appropriate if damage to the filting and equipment is to be avoided.
Under beavy loads it would be possible for tbe fitting to become damaged while the mooring Ijne
is still intact. A deformed fitt ing ma y be unus able, where the overstress;ng of a. line may not be
obvious until it breaks.
[n tenus of repair expense, damage to linings and equipment is usual[y more serious than damaging
or breaking a line.
The recommended strength standard for mooring fittings and equipment is therefore that the fitting
or piece of equipment and ils components should be able to withstand, without permanent de-
formation, loads equiva.lent to the speci fied breaking str ength of the mooring line.
4.3 Existing Standards
Numerous national standards (or mooring fittings exist, but tbey often do not provide sufficient
information to establish the actual strength. Tn some cases a 'SWL' is stated, but no safety factor;
in others an 'applicable line' is li tcd, but no information as to how the line stre.ss relate,s to fitting
stress is given; in yet other case the hne position, direction or quantity may be missing. In com-
paring two fittings designed to djfferent standards, it is possible that the obviously weaker design
lists a lligher raled 'load'. Listed 'load' differences between two fittings of equal sizc may be as much
as a ratio of I to 10, most of which can be due to different definitions of 'load' , safety factors and
load application.
Mooring fitlings are often speci fied in nominal sizes such as 300mm or 400mm djallle.le,r bollards.
Fittings with the same nominal size manufactured to differenr standards may have widely varying
actual strengtJl capabilities and safety faltors.
Table 4.1 gives a sUlllmary of cunent mooring equipment safety factors and design crite,ria as far
as these can be determined from some existing standards. As can be seen from the lable, I hese
parameters cannot easily be established for all mooring eqrnpment. [n the absence of recognized
design criteria, manufacturers rely on internal criteria developed during the design, testing and
manufacture of mooring equipment. They may also manufacture moorin g equipment to recognized
standards that speci fy dimensions, materials of construction, tolerances, quality aSSllrallCC and testing
procedures, as well as the maximum loads or maximum rope or chain sizes that can be accepled.
A list of widely used standards (ISO, British and Japanese) for mooring equipment i, contained
in Table 4.2. These standards can become defacto industTy standards as owners experience satis-
factory service from a particular manufact.urer's equipment. The ISO standards are the recognized
international industrial standards on which many national standards are based. However, without
universally recognized SI renglb standards, evaluation of new offerings and definit ion of strength
limits by designers and operators i - difficult.
When the applicable mooring line ize i determined from the existin g standards, it is recommended
to check the allowable minimum breaking load (MBL) of the rope, if specified, along with the
specified applic.able rope size because tIle rope breaking strengths may be different among standards
and depending on the grade.It is to be noted that Regulation 15- 1 of SOLAS Chapler V (Ch 11-1(3-4 from InNS) require (Ill
emergency towing compo neoL tQ ha ve lb e spec.ifietJ working streng'tb for 'Ill rclt:v;Hll towline a ngles. i.e ..
up to 90 degrees horn tht; ship's centreline to port and starboard. and 30 degrees verlica l downwards.
Since no conventional closed chocks designed to the eurrent standards will meet the above loading
requirements, particular attention should be paid when closed chocks are ordered for compliance
with the above regulation, or if closed chocks for SPM will also be used for I he emergency lowing.