Sunday, February 10, 2008


Galvanic Isolator, 2/9/2008

As I mentioned earlier, one of my planned projects was installing a galvanic isolator. This was recommended, but not required, by both our surveyor and BoatU.S.

Although Mariner II wasn't showing any serious problems with corrosion, zinc loss during the summer is difficult to address, as it involves diving under the boat (which I did once this past year). Diving under to replace a zinc isn't that bad as long as the sea nettles aren't there keeping me company, but usually they are. A galvanic isolator should, minimally, slow our zinc loss enough so that it can be replaced once per year, during winter haulout.

I considered several brands, including Guest, Yandina, and ProMariner. Ultimately, I installed the ProSafe 30, without a monitoring system. ABYC recommends that galvanic isolators be self-tested and monitored to ensure that the AC ground wire is uninterrupted. The isolator alone does not meet this recommendation, but thousands have been installed this way without problems long before ABYC made their recommendation. Since the monitoring system costs more than the isolator itself and complicates installation considerably, I opted to skip it for now. The ProSafe 30 does allow me to add the monitor later, but for now I will just plan to test it routinely (spring and fall) with a diode tester. The test is easy: with shorepower disconnected, attach one lead of a multimeter (in "diode test" setting) to each side of the isolator and get a reading. Switch, and test again. Both readings should be the same (within 10%), and both between approximately .7 and 1.5 volts.

On our boat, the isolator fit nicely in the starboard storage area below the helm. I was able to simply cut the ground wire, attach insulated ring terminals, and connect them.


Anonymous said...

Couple questions. What size isolator did your install? What is your amp usage? Who did you order your isolator through? Check out my blog;

Trawler Joe said...

I installed a single, 30A isolator (ProMariner #22033), which I bought from for about $160 plus shipping. If you don't trust lesser-known internet vendors, you can get it from some of the bigger names too but pay a bit more (I think Boater's World is about $200).