You could try reading current with your multimeter instead of voltage. Small stray voltages likely exist when measuring between lead and SS even in fresh water but I doubt they will sustain much current.
Just as an example of magnitude very roughly if there was a current of 1 amp continuously in normal soil it would corrode about 20 lbs of steel in a year. If you are reading less than 0.5 milliamp I would say those two surfaces are not going to have much corrosion between them. If you are seeing over a milliamp then there is an issue. The circuit requires two paths, the dissimilar metals in water and then something on the boat connecting them together. Some advice has been to connect the mast, standing rigging and keel together but do not ground them to the boats electrical system. That may be difficult if items like the VHF antenna is mounted to a metal bracket on the mast. You can test for this by measuring the resistance between the mast and ship's ground. Anything under 10 ohms would indicate a connection. Michael Brown Windburn C&C 30-1 Date: Tue, 14 Aug 2018 13:41:43 +0000 From: "Della Barba, Joe" <joe.della.ba...@ssa.gov> Voltage readings between what and what? Joe Della Barba Coquina Sent: Monday, August 13, 2018 7:25 PM Hi Alan The readings I posted are at anchor in the Thousand Island area. I almost never plug in during the cruising season. I only use shore power to charge the batteries during winter layup when the solar and wind are removed, every 6 to 8 weeks So today I did more testing. I disconnected the positive cable for the start battery and I still saw 0.02V at the prop shaft. So I ruled out that as an issue. I disconnected the battery charger and still saw voltage. Next I took the wind generator out of the equation and the results were the same. Next I disconnected the windlass, same results. Next I moved inside and checked for voltage on the tube for the centre board pendant. Saw 0.25 V. I removed the positive cable to the house electrical panel. Still saw voltage. Am I doing this right. My memory tells me that the way I?m testing might be creating some kind of battery but my memory might be tricking me. Could really use some help from any electricians or corrosions specialist out there. Mike C&C 37 K/CB Shoal draft Persuasion Stormont Yacht Club
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