Stray Current Isolation Testing?

[zstine]

Originally Posted by boatbod

I once worked on a C&C who's lead keel was so reactive that both the keel and saildrive were eating each other away despite all attempts to get coatings to stick etc. In the end we disconnected the bonding wire between the two components and now both coexist quite happily. The keel floats at it's own potential and the engine & saildrive (a Yanmar) are bonded to the vessel grounding system and galvanic isolator.

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Boatbod, I'm loosing a lot of lead (no outdrive though) and am considering lifting the bonding to the keel. When you did this, did you put a separate anode on the lead keel or is lead noble enough to not require it when allowed to float.. similar to my bronze thru's which float without protection?

[boatbod]

Originally Posted by zstine

What about those low -145mV readings on the bronze unbonded through hull. Does that provide any info/concern?

I wouldn't worry too much about that. Unbonded bronze thru hulls float at wildly low values. Unless you see pink on the bronze, leave them alone.

[boatbod]

Originally Posted by zstine

Boatbod, I'm loosing a lot of lead (no outdrive though) and am considering lifting the bonding to the keel. When you did this, did you put a separate anode on the lead keel or is lead noble enough to not require it when allowed to float.. similar to my bronze thru's which float without protection?

We considered doing that but ultimately did not. After two seasons it still looks ok. My preference would be to let the keel float and remain isolated. Biggest downside is implications for lightning grounding.

[Doodlebug]

It normal for a boats to have the battery switch turn off and still have DC power going to the bulge pumps. That would explain why your reading voltage in the bulge water when the battery switch is off. I wonder what would happen if you disconnected the fuse or wiring? That's assuming the bulge wiring is bypassing the battery switch.

[Cavalier]

Originally Posted by Doodlebug

It normal for a boats to have the battery switch turn off and still have DC power going to the bulge pumps. That would explain why your reading voltage in the bulge water when the battery switch is off. I wonder what would happen if you disconnected the fuse or wiring? That's assuming the bulge wiring is bypassing the battery switch.

..could also be worth checking to see if there's a small leakage current on the bilge-switch itself, if part of the wiring to the bilge-switch or pump is partly submerged and insulation is failing, then it could explain some of the "DC off" losses, in addition to the obvious anode issue.