What is the issue?Yacht rigs and spars are largely assembled with fittings containing dissimilar metals. Typically stainless steel in the form of gooseneck brackets, spreader brackets etc mixed with aluminium rigging. Mixing different metals and salt water causes an aggressive corrosion called electrolysis. This is particularly prevalent up to six feet above deck level and at the mast heel below decks where salt water can collect and remain for extended periods.
Why address this?Unchecked electrolytic corrosion is a prime contributor to rigging and spar degradation and failure. Worse, electrolysis developing at the base of the mast causes swelling between the mast wall and the insert. This causes a dangerous situation to develop where the swollen and weakened mast wall is susceptible to splitting. Should this happen, the rigs high compression load would drive the mast wall out and over the heel plug. An instant mast height reduction is the result, effectively removing rigging tension with disastrous consequences.
How to address this?Completely insulate all fittings by placing a thick layer of duct tape to act as a ‘sleeve’ around the aluminium. In cases where extensive contact is required, such as on mast mounted winches etc, utilise plastic or wooden insulating pads.
Check your vessel by removing all fittings and examine for electrolytic corrosion including the mast heel. If any exists, repair the rigging as required.
When refitting or putting in place a new rig, stick a thick layer of duct tape to the mast areas where the non-aluminium fittings are being set in place. Shape the duct tape so that it matches the corresponding shapes of the fittings but allow the duct tape shape to extend the fittings by about three millimetres all around. Once you have ensured the duct tape ‘sleeve’ completely separates the two metals mount the fitting as normal with aluminium rivets.
Make certain the mast heel has a drain hole in the very bottom to allow water to escape. The mast step area must be self-draining and kept dry.
The result of implementing this simple duct tape sleeve technique and some electrolysis vigilance, should provide reliable rigging that will give years of service.
With thanks to:Michael Harpur, Yacht Obsession.
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