I leave my boat in salt water all winter, I change my zincs in the spring,and dive mid summer. I have always hung a zinc over the transom grounded to the block (shaft) & rudder shaft. I have never checked the resistance between the block & the zinc, I know 0 ohms would be ideal, but I know their is some res. in the ckt. . about what would be the max res. that would be acceptable ? assuming all connections are clean.