Specifications

79
5.8.15 Mooring hazards
The phenomenon most likely to result in early failure of the mooring is galvanic corrosion
between different metals in sea water. When a mild steel shackle is coupled to the AISI316
stainless steel Waverider the shackle may fall apart within one month. Even the coupling of
AISI304 and AISI316 stainless steel will lead to early failure.
In case it is necessary to couple different metals, an electrically insulating element should be
used.
The second largest cause of early failure is the corrosion in sea water of steel wire rope
without zinc protection. Rope made of mild-steel filaments will break within one month under
unfavourable conditions. AISI316 stainless steel filaments are not much better. The thin
filaments are highly sensitive to concentrated corrosion, called pitting. Experience has shown
that galvanized steel wire rope with nylon covering is insensitive to corrosion provided that the
rope ends are closed or stay unloaded. Of course, synthetic fibre ropes are also acceptable as far
as corrosion is concerned.
Kinking may also result in failure of the mooring. Synthetic fibre ropes are apt to kink
when the rope has an asymmetrical (layed) construction, but the braided and plaited
constructions are free from torsion when loaded and therefore not liable to kinking. At the end
of the chain coupling a swivel is placed for extra safety. The swivel is made from AISI316
material with a thrust bearing and a self lubricating nylon ring placed in between the steel faces.
Another cause of failure was found to be that the screwed parts of a mooring unscrewed
themselves. Therefore, the number of screwed parts should be reduced to a minimum. Nuts
must be secured with a steel ring or split pin placed in a hole through the threaded part above
the nut. The screwed pins of shackles should be properly moused with metal wire of the same
composition as that of the shackle or with nylon cord or patented nylon tiers. Make sure that
nylon tiers do not contain metal parts.
Three further causes of mooring failure are due to human interference. The first one is the
cutting of the mooring line by ships passing the buoy too closely. The second one is human
curiosity and pilfering. Informing the local public of the importance of wave information and of
the role of the Waverider may reduce their interference. Furthermore, the salvage reward should
not be too tempting. The third one is the use of the Waverider as a mooring buoy for small
boats.