range could indicate DC stray current
migrating through the dock ground sys-
tem. This will require investigation.
4 Assuming the dock’s basic potential is
between –400 mV and –800 mV, com-
pare that number to the boat’s basic
potential both when plugged into the
dock and when unplugged.5 The basic hull potential with the boat
plugged in should fall between the basic
dock potential and the boat’s unplugged
potential. Although the exact reading for the
unplugged boat may not be the ideal value
for the specific boat you are checking, it may
be acceptable if anode consumption is
within the acceptable service limits of three
to ten months for a typical recreational boat.114 electrical systems troubleshooting
Proper electrical location of a boat’s galvanic isolator, from ABYC Standard A-28. (Courtesy ABYC)