Keep Your Drive Alive..Part 2....Ed Sherman

In my last installment, I explained a bit about what galvanic corrosion is and what a galvanic isolator can do to minimize the effects of this phenomena when you are plugged in at the dock. Now we need to take a look at some of the key specification issues and installation considerations you need to make if you decide you're going to install one of these units on your boat.

First of all, galvanic isolators have some important ratings you should look for to make certain you have the right one for your system, and that it meets ABYC requirements.

ABYC requires that all galvanic isolators meet some pretty tough standards in terms of their design and construction, and further, that a manufacturer gets third party certification that they do. ABYC is concerned that if one of these units fails, all safety ground protection on your boat would be eliminated. The units are available in two flavors these days, with a status monitor (not recommended) and one of the fail-safe design. There have been wholesale problems with the status monitoring devices false alarming over the last four or five years, so I strongly recommend getting one of the fail-safe rated units. These have proven to be reliable and trouble-free. In fact, the status monitoring variety has proven to be so problematic, that I'll bet you may have a problem even buying one today. Anyhow, these units get mounted in series with the green wire at a point as close as you can get in to the back side of the shorepower inlet socket on your boat. The diagram below, which comes right from the ABYC Standard A-28, which covers galvanic isolators, illustrates where we'd like to see it:

These units need to be rated for amperage handling capability to match your shore power service at the least. 30 amp, 50 amp, 100 amp. They need to be installed in a relatively cool, ventelated location as they've been known to get hot. Also, when splicing them into your green wire, no friction type electrical connectors should be used, only solid butt type connectors, or preferably ring type terminals carefully crimped on. Most important, if your boat uses gasoline vs. diesel for fuel, it should be rated for "ignition protection". If it doesn't say so on the unit, assume it is not, and installing it in a gasoline engine room, or fuel tank area of your boat is extremely dangerous. The photo below shows a unit installed on J-109 saliboat. Notice the green wire attached via a ring terminal.


If you have any doubts about your abilities in the area of electrics, I strongly recommend that you find an ABYC certified electrical specialist to do this for you. You can find one at, just click on certified technicians.

But I already have a galvanic isolator on my boat and the anodes on my drive unit are disappearing in a matter of weeks!

If you are certain that you are galvanically isolated from your dock mates, or let's say you keep your boat on a mooring and never plug into shorepower but your saildrive or outdrive anodes look like the one shown below (just to right of center) in a matter of weeks:

OK, galvanic isolation could still be a problem, only this time it's with the metal on your own boat. It can also be, and is more likely to be caused by what is known as an out of wack anode to cathode surface area relationship. Now thats a mouthfull. What's being described here is basically the mount of anode exposed to the electrolyte vs. the amount of underwater metal exposed to the same electrolyte. One of the primary things to remember here is that your drive's anodes are only engineered to protect your drive, nothing more and I do mean nothing! Unfortunately a lot of boat builders and boat owners do not take this fundamental into consideration. You may need to add more anodes to the bottom of your boat and be sure these anodes are tied into the same grounding system as your engine, (the green wire).

One of the problems I've run into this year was with a fellow with a sailboat who lost his drive to extreme corrosion. Turns out the lead ballast keel had gone naked, at least in part due to weekly wet sanding by the boat's caretaker to keep a racing level finish on the bottom. Well, eventually he sanded right through the barrier coat, exposing bare lead. The boat builder had coated the lead with an epoxy barrier coat; this is as it should be because the epoxy makes a great insulating (non conducting) barrier from the electrolyte (the watter the boat is floating in). This should be done with all underwater metal. Epoxy barrier coat, or paint systems such as used on your drive when new, will effectively insulate the metal from the electrolyte, controlling the anode to cathode relationship, and helping to minimize the amount of anode material you need. Removal of this protective coating alters the relationship and anodes will become consumed more quickly until the are completely gone. Next on the food chain? Your drive unit, and the corrosion will begin at the exposed metal and then begin to lift the rest of the paint off the drive. If you don't use your boat too often, and aren't paying attention your drive could end up looking like one of the beauties shown in the photo below:


So, short of a battery level electrical leak throughout your boat's bonding system or exiting into the water through your drive unit, proper care in the form of ensuring you're equipped with a galvanic isolator, that your underbody is properly painted with a good barrier coating as well as anti-foulant and that supplimental anodes of the same material as those on your drive unit (often aluminum vs. zinc) are the tickets to keeping your drive alive.

This is an area that if you are completely lost in your understanding of the phenomena presented here, an ABYC certified corrosion specialist can help. Go to and click on Certified Technicians to find a certified tech in your area.