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Underwater Maintenance: Brief Introduction to Boat Zincs

If you are buying a used boat, or just maintaining a boat, the zincs - hull anodes or sacrificial anodes - are an essential part of her protection. Boat zincs which are not working can lead to a fatal failure of thro-hull fittings. Many boats have sunk on their moorings because the boat zincs were not replaced or fitted in the first place. For more details, visit https://underwaterdivingblog.wordpress.com/2021/09/16/underwater-maintenance-brief-introduction-to-boat-zincs/

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Underwater Maintenance: Brief Introduction to Boat Zincs

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  1. Underwater Maintenance: Brief Introduction to Boat Zincs

  2. Introduction IF YOU ARE BUYING A USED BOAT, OR JUST MAINTAINING A BOAT, THE ZINCS - HULL ANODES OR SACRIFICIAL ANODES - ARE AN ESSENTIAL PART OF HER PROTECTION. BOAT ZINCS WHICH ARE NOT WORKING CAN LEAD TO A FATAL FAILURE OF THRO-HULL FITTINGS. MANY BOATS HAVE SUNK ON THEIR MOORINGS BECAUSE THE BOAT ZINCS WERE NOT REPLACED OR FITTED IN THE FIRST PLACE.

  3. HOW DO BOAT ZINCS WORK? The zincs -metallic zinc are just lumps of metal which erode electrically. Your metal hull fittings, propshaft and propeller (and outboard motors too) will naturally corrode in water as small electric currents remove their metal and take it, atom by atom, to another metal which is more attractive (and acts as a cathode). With boat zinc, it is the zinc itself which acts as the anode, the metallic zinc become more 'attractive' to the cathode as we mentioned. So, the boat zinc corrodes away, leaving the important hull fittings safe. The material of the hull fittings may be made of a variety of metals - brass, bronze, stainless steel - or even high quality plastic (hopefully not low quality). Apart, obviously, from plastic, these metals have differing 'electrochemical potentials' and those which corrode more slowly are described as more 'noble'.

  4. How to Check Boat Zincs? It is essential that the sacrificial anodes 'work' - that is that they are sacrificed and corrode before the other metals and protect the coated parts. That's why they are for that. Their working life will depend on many factors e.g. location - marina or swinging mooring. Basically, these will weigh typically 1/2lb or less. Larger power boats may have 4 or 5, and a 35' steel cruising yacht may have 6 or more, often with one or two protecting the rudder. When you inspect them, on the hull, they should be pitted (though they could be new and clean), and once they have reached 50% of their original weight (you should be able to estimate this by eye), they should be replaced. If they have a hard white carbonate deposit or are fouled, then they are not doing their job. The metal should be bare - paint stops them working.

  5. Conclusion Many skippers change the boat zincs at every annual haul out, though there is no need to do so if they are working and not below 50% corroded and the boat is slipped annually. The boatyard or underwater maintenance company, though, will always suggest it.

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