Protect your sterndrive with anodes from West Marine.
Galvanic corrosion can be an expensive problem for sterndrives. If left unchecked, it can deface an outdrive’s lower unit and eventually reduce it to a pockmarked piece of junk. The best way to avoid this sort of tragedy is to protect your outdrive with a set of sacrificial anodes, which West Marine offers for most makes and models of drives.
What is galvanic corrosion?
Galvanic corrosion is the process that leads to the breakdown of metals immersed in an electrolyte such as salt water. When dissimilar electrically connected metals are immersed (creating a galvanic cell) a current is generated which destroys the least noble of the two metals (the anode). Many people wrongly refer to this process as electrolysis.
In the case of outdrives, when a lower unit’s aluminum case is immersed in water, it becomes anodic to other metal parts such as the drive’s stainless steel prop shaft, fasteners or oil drain plug. In the ensuing galvanic reaction, the aluminum case sacrifices itself to the more noble metal parts. Evidence of this can be seen in the pitting of the aluminum case.
How do outdrive anodes work?
Continuing with the outdrive example above, sacrificial anodes take the place of the drive’s aluminum case as the least noble (more reactive) metal component of the drive. As the least noble metal component, they sustain the galvanic reaction, thus saving the casing of the drive. For anodes to be effective, they should never be painted. We also suggest that anodes be changed when the galvanic reaction has reduced their mass by 50 percent.
Types of Outdrive Anodes and Anode Kits
As protection against galvanic corrosion, outdrives require various shapes and sizes of anodes which install on multiple locations. Examples of outdrive anodes include trim tab anodes, lift ram anodes, bearing carrier anodes, gear case anodes and gimbal plate anodes. While anodes are offered individually, we suggest you purchase your anodes as a kit which contains all the anodes you need for your make and model of outdrive. West Marine sells anode kits under the Martyr brand. Kits are available for most manufacturer’s outdrives including MerCruiser, OMC, Volvo Penta and more.
Anode Materials
It has been shown that anode performance can vary with the type of water (salt, brackish, fresh) where a boat is used and the material of which the anode is made. For this reason, anodes are offered with a choice of materials — zinc for saltwater, aluminum for salt- or brackish water and magnesium for freshwater.
Available Anode Brands
Brands of anodes available at West Marine include Martyr, Sea Shield and Sierra.