I noticed some pretty bad corrosion on my two Frigoboat Danfoss compressors and the related lines that are keeled cooled. They are behind a corner and I havenít looked at them in awhile, and I was pretty shocked how bad they were rusting. The copper lines going to the keel cooler were also pretty heavily corroded.
There are two zincs on the keel cooler for these compressors. My diver that comes once per month is supposed to be replacing the zincs, but when I talked to the actual diver doing the work recently he said he canít see anything down there and is doing everything by feel, so now I wonder if all my zincs have been depleted for awhile. All the zincs were replace last year at my last haul out, and the boat was in fresh water for 3 months of that year and the Bahamas for a month. I should have looked at the zincs in the Bahamas I realize now. I have been in this marina for about 8 months.
Iím scheduled for a haul out tomorrow morning so I can check all the zincs and just do a basic inspection, and in the between time I started doing some testing with my silver cell and multimeter. I put the electrode for the cell to the negative on my multimeter and tested some things with the positive electrode. Here are the DC voltage readings to some things I tested.
Bonding system -232mv
Copper wires running from the compressors to the keel cooler -232mv
A transducer for my Garmin system -125mv
According to this table, the readings should be in these ranges. Iím not familiar with galvanic corrosion or much concerning electrical so maybe Iím thinking about this wrong, but if itís less negative (higher reading) donít I have a problem? Also, how do I measure if there is a stray current at my marina? There are some pretty crappy steel hull boats a few slips away from me so I wonder about that. How do I test for that?