Corrosion is perhaps the most frequent issue associated with modern saildrive units. There are a few different causes for premature or excessive corrosion on these units, and if certain guidelines are followed, problems can be eliminated.
The number-one thing to remember about these drives is that the anodes on the units are engineered to provide corrosion protection for the drive only! Manufacturers recommend anode replacement every 100 hours, but it is of absolute importance to remember that this recommendation is based on some important assumptions that only the boat owner can maintain control over.
The first step in ensuring that your drive’s anode(s) provide good service is to make sure that any of the factory original paint on the drive leg that gets scraped off gets touched up. Also, you need to be certain that the anode material is appropriate for the water your boat stays in most of the time. The standard zinc anodes won’t do the job in fresh water and may even fail in brackish water. For brackish water use aluminum alloy anodes, and in fresh water magnesium alloy anodes are the best choice. Anodes should be replaced when they are 50-percent depleted.
Marine electrolysis can be avoided in most cases, by simple, practical techniques. Most important are:
1. Defining areas that are most vulnerable to electrolysis.
2. Monitoring, both above and below the water line. (above is not sufficient)
3. Knowing the location of the sensitive sites in all thru-hull fittings. Bonding wires are usually attached to thru-hull fittings with wires to zinc plate. Assure that bonded thru-hull underwater lights, trim tabs, and other appendages are properly connected.