Put aluminium in the water near steel and an electrical current develops between the two metals, like the flow in a car battery. Eventually, the flow of electricity from the more galvanically active metal -- the aluminium -- will cause the aluminium to corrode like the anodes in the car battery. Place a piece of a more active metal, such as a block of zinc, on the hull of an aluminium boat, for example, and the zinc, not the boat, will corrode. Proper installation of the zinc anode is the key to this type of protection.
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Things you need
- Drill and bit
- Adjustable wrench
Locate a bare metal surface below the waterline on which to mount the zinc. If the zinc is to be mounted to the hull of an aluminium jon boat, for example, ensure that the area where you mount the zinc is unpainted bare metal. Once you've established the location for the zinc, hold the zinc in place as a template and mark the locations where you'll drill the mounting holes through the hull.
Drill the holes through the hull with a drill and an appropriately sized bit. Some boat hulls have pre-drilled holes to accommodate the placement of zincs. The zinc must be as tight against the hull as if it were extra skin on the hull. This maintains solid electrical contact with the hull for the best cathodic protection.
Slip the bolts through the mounting holes on the zinc and fit the bolts through the holes in the hull. Slip the ring terminal of the boat's bonding wire, part of the boat's common ground, over one of the bolts. Thread the washers and nuts onto the bolts and tighten the bolts with an adjustable wrench.
Tips and warnings
- Outboard motor propeller shafts, propellers and lower units are equipped with zincs when they are manufactured. Their replacements are specially manufactured to fit in recesses on the parts, although they still bolt into place. You must monitor the condition of theses zincs, like all others, and replace them as necessary.
- Some zincs use one bolt, in the centre of the zinc, to minimise the number of penetrations through the hull. Other zincs have bolt holes in each corner, to ensure the best possible electrical contact with the hull. Ultimately, the choice between the two types rests with the boat owner.
- Zincs deteriorate over time. As they corrode, they grow smaller. When a zinc is one-half its original size, replace it.
- Zincs must be installed when the boat is out of the water.
- Never paint over a zinc. A painted zinc offers no galvanic protection.
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