galvanic corrosion on keel?
 

Not an A4 question but I'm sure someone here can help. A friend's boat was pulled out of the water on the weekend for a survey and they found significant corrosion on the keel. My guess is its galvanic corrosion. The keel was 100% perfect when the boat splashed in May 2021 and has only been in fresh water. Thoughts?

Attachment 15999

With the speed at which that occurred (2~3 months) my thoughts go immediately to stray current corrosion.

Questions:

1. Is his keel grounded?
2. Does your friend have shore power?
3. Is he slipped near other boats?
4. Does his shore power system have an AC-DC ground bond?
5. Does his shore power have a galvanic isolator?
6. Is his shore power main switch an ELCI?

Worse than stray current, I'd say forced current.
Consider yourself lucky it didn't go the other way. You would have dissolved your propeller! Had it happen to me. My 12" Michigan wheel came off the boat at 9.5" due to a bad ground cable between the battery and the engine block.

Below is what I know. I'll check with my friend and get the missing answers. Sounds like you agree that it's galvanic corrosion. Thanks!!

Questions:

1. Is his keel grounded? - I'll ask
2. Does your friend have shore power? - Yes
3. Is he slipped near other boats? - Yes
4. Does his shore power system have an AC-DC ground bond? - Will check
5. Does his shore power have a galvanic isolator? - Will check
6. Is his shore power main switch an ELCI? - Will check

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Caveat - don't swim off your boat or the docks until this issue gets resolved.

Very good point. We're pulling the boat today to repair and get to the bottom of the issue.

Another question. Does the owner leave the shore power plugged in all the time? Dan
S/V Marian Claire

I know everyone does their own thing, but I cannot for the life of me see a reason to keep a 30 amp shore power plug connected to the boat 365/24/7.

I have a 5w solar panel that keeps my start battery at 100% every time I come to the boat, and 30w solar panel that keeps my 230 AH house bank at 100% every time I come to the boat. I don't even take the batteries home in winter anymore, as the sun at 38° Latitude is still plenty to keep them up all winter.
I understand a fridge and stuff (which I don't have, but put adequate solar to run that at the dock.) When you are on board and want A/C, plug the boat in. I have neither, although A/C is MUCH higher on the list than a fridge with these newer tech coolers.

I do but to isolate my boat from the handiwork of others I do not have an AC/DC bond.

Living in a population center it's risky leaving solar panels out if you want to keep them.

Hi Dan, yes it's plugged in all the time. Got to keep the beer cold :)

Waiting for a Digital Clamp Meter to arrive in the mail :)

Do the marina folks know about this damage? Any other boats in the immediate vicinity been pulled lately?

Bill

That totally changes the game:cool:, as does Neil's comment about theft. :mad:

[off topic]
I didn't mean to leave the impression I've experienced a theft problem but neither do I leave easy bait out on the deck either. I've never suffered a theft loss, the closest I came was several years ago when my slip neighbor did. The nogoodniks crowbarred his companionway open and made off with all his electronics.

IIRC. If your AC and DC grounds are connected and you do not have a galvanic isolator and your shore power is connected, you have created a path for stray current to pass from the water thru your boat and to the ground ashore.
To prevent this on the MC I do not leave my shore power connected. You never know when a stray current issue will happen.
Obviously I would choose a different approach, installation of a galvanic isolator, if I lived aboard.

Dan
S/V Marian Claire

When I purchased our boat, one of the very first projects I did on it was to install a galvanic isolator. It was very easy. We traveled to a lot of marinas in our first few years, and as you have seen, galvanic and stray current corrosion can happen very quickly.