Anodes, hull potential & bonding

[Wood]

I have a new to me Bayliner 4588. I purchased it in Ontario Canada and brought it to New Hampshire last week.

We did a short haul survey. Neither the owner or surveyor could tell what type of anodes were used: shafts and main on transom about 6x12x3/4. And stern thruster apparently not on bonding system with 4 bullet anodes about 2".

So, I got it home and am checking the bonding system and hull potential with a AgCl half cell. Bay is salt/brackish.

I'm on a mooring. Nearest neighbor is 75 feet.

Turn off all power, battery switches, breakers, physically disconnected thruster batteries, the works, except automatic bilge pumps. Lowest pump was in water so I lifted it out. Checked all bilge pumps for ampicity. Zero

With the half cell readings are -216 -220mv at all bonded locations:. Engines, through hulls, shafts, striuts , rudders, main anode attachment, etc.

Checking the thuster mount (apparently not part of the bonding system) read -100mv.

Next steps are to call a diver and hang a big anode over the side and see if that makes a difference.

Aside from equipment calibration ( I used two multimeters) any suggestions what I should be looking for?

[Wood]

Follow up:


I spoke with the reference electrode supplier. He says the anodes are probably zinc and since the boat was fresh water they are probably passivated.


He suggested wire brushing anodes and retest.


He also suggested using new Al hanging anode and testing that alone. Reading should be -1100mv. That would confirm reference electrode operation and accuracy.