Anodizing, a process of electrically causing the formation of a tough oxide film on the surface of aluminum, slows pitting, but anodizing will not
prevent pitting or crevice corrosion.
Aluminum is very active galvanically and will sacrifice itself to any other metal it contacts either directly or indirectly. Aluminum is anodic to
everything except zinc and magnesium, and must be electrically isolated from other metals. In this case, paint, bedding, and a non-conductive plastic
or rubber isolator should all be used together. Unlike tankers, small metal boats are not designed with an appreciable corrosion allowance
Regardless of the bottom paint used, zincs must be used to control stray-current corrosion, to which we can become victim with a metal boat, even
without an electrical system! With a scratch at the bow, and another at the stern, the boat itself becomes the preferred path for any ambient currents
in the water.
Zinc anodes should always be used on an aluminum boat, and generally in the same quantities as with a steel boat, in order to prevent stray-current
corrosion.
After the first few months, inspect the zincs. If they appear active but plenty of material remains, the zincs are doing their job. If they are
seriously wasted, the area as well as the weight of zinc should be increased.
Of course, welding zincs on is best, but for an aluminum boat, the zincs will instead usually be bolted to studs welded onto the hull plate, or bolted
using stainless bolts into a heavy bolting plate welded to the hull. Good electrical connection between the zinc and the hull is
imperative. |
Hi Amigo!
