The stainless steel shackle & weakened link found on the chain of the mooring Classique dragged in June’14
Excerpt from “Northland Regional Council Mooring Guidelines”
“Care must be taken with moorings that dissimilar metals are not used, eg mixing steel & stainless steel.
When different metals are in contact & immersed in salt water they set up an electrical potential. The salt in the water makes it a good conductor.
The result is the least noble metal (lower on the galvanic scale) will corrode.
If different metals are used they should be isolated where possible by non-conductive sheathing.”
It was rather disconcerting that Bolton found on 2 of these Heavy duty Moorings Stainless Steel shackles had been used with alarming deterioration in the diameter of the links they were attaching to.
On the 1st occasion Classique was able to move onto the next mooring whilst the contractor lifted & remedied the risk of failure.
The 2nd time this same reduction of steel was seen in the proximity of the stainless steel shackle on the chain of the mooring Classique dragged on the night of June 10th recently.
This weakness was such that if the mooring anchor had held, it is very likely that the link would’ve failed & let Classique break free to wash up ashore.
It happened that as the mooring anchor offered no appreciable resistance , the link was not even stressed or stretched.
As the same contractor is used to service these Auckland Council Moorings, it is obviously negligent for this problem not to be recognized – in fact it’s probably left up to that contractor to supply the components used in the mooring system