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Dezincification of dodgy marine fittings now appearing in imported boats ANOTHER HOLE IN YOUR BOAT BY MICHAEL PIGNÉGUY E when my hand slipped off a fitting that I was tightening with a lectrolysis; the very mention of this word can strike spanner and bumped against a through-hull fitting that promptly fear into the heart of many a salty old sea dog. A simple broke off. The problem was that we were afloat, something that definition of electrolysis is that when there are different was going to change unless I quickly plugged the hole. I have a metals placed in a conductive liquid an electric current will wooden plug attached to every through-hull fitting on Zuben so the flow, and this electric current will slowly erode the softer metal. incoming tide was easily halted. But it meant a haul out, using the As far as boats are concerned, the conductive liquid is of course floating dock in Westhaven to install a replacement fitting. sea water which in this case is called an electrolyte. It's the same At that time Zuben was six years old and I had regularly been principle as the basic construction of a battery where there are a doing one of the recognised checks on the series of pairs of different metal plates brass through-hull fittings by scratching separated by an electrolyte. them, especially on the threaded lengths, The problem with boat fittings is that if they are subject to electrolysis, the weaker to see if the metal was still bright and yellow. And yes they were, even the one one will eventually fail. The Royal Navy that had just broken. found this out in the early 1760s when they fitted copper sheathing to the bottom It wasn't a difficult decision to change all the boat's skin-fittings to of HMS Alarm only to find that the copper Glass Reinforced Nylon 6 which were nails holding the sheathing onto the hull International Marine Certification reacted badly to the iron hull fastenings, with the result that the copper sheathing Institute Certified to ISO 9093-2. This had to be removed. By 1769 however, was done at our regular haul out, which hull fastenings were made using a copper followed soon after, and I was shocked alloy which met with very favourable to find that another three fittings broke during removal. I got into a discussion results after the application of copper with an owner of another European sheathing. Further experimentation with yacht which was younger than ours, and alloys followed and finally in 1786 a who was also plagued with the same suitable mix of copper and zinc was found to be best for hull fastenings on vessels Composite fittings are now approved and don't fail problem. He knew of five other yachts out of Europe that were similarly afflicted. fitted with copper sheathing. With this success every ship in the navy was eventually re-bolted and copper sheathing remained the Boat builders Beneteau advised at the time that "for more than standard method of protecting a navy vessel's underwater hull, a decade they had been installing brass through-hull fittings... that had been made in Italy for over 40 years". The composition of the until the advent of antifouling paints. fitting is defined as: 38 percent zinc, two percent lead, 58 percent You would think that, 237 years later, we really would have sorted this problem out by now. But no, electrolysis in boats is still copper, with the remaining two percent made up of aluminium, tin, a major problem. nickel, steel, manganese, antimony and arsenic. It's not known where some other European yachts experiencing A case in point is our own boat, a Beneteau 44.3 that we bought electrolysis problems are sourcing their through-hull fittings, but new in 2005. Last year I was working around some hull fittings 38 Professional Skipper July/August 2013 www.skipper.co.nz