This has to be galvanic corrosion, correct?

[EmeraldCoastSailor]

Seems like all of a sudden a few months ago I started suffering serious damage to my iron keel. My yard guy thinks it is from an electrical problem on neighbor boats. I am fixing the boat but not sure I can do much more than hang a zinc fish. 2009 Beneteau 343

[SailingHarmonie]

Are you sure you do not have stray current problems on your own boat?

This is not "galvanic" corrosion this is stray current corrosion, the result of electrical currents flowing where they are not supposed to. Many people call this "galvanic" corrosion, but that drives some people on this forum nuts... Adding zinc will not fix this problem.

The current flow might be between boats, or between parts of your own boat.

Just one example of what could happen: You have a wire on the positive side of your bilge pump switch sitting in bilge water, and leaking current that is flowing out of the keel, and back to the battery through the prop and engine ground.

This is a complex topic... you either have a lot of reading to do, or find somebody who is an expert.

[CarlF]

As SailngHarmony suggests, go look at your bilge pump and bilge pump switch wires. A frayed wire or a splice that has fallen into bilge water is a very common culprit. The location of the rust on the keel is close to where I assume the bilge pump is located. It could be coming down the keel bolts.

I’d consider replacing the float switch even if you can’t find anything wrong.

[senormechanico]

I agree it's probably on your boat. That corrosion is at the TOP of the keel which tells me it's the closest to the source of the electrical leak.

[boatpoker]

As a retired Certified Marine Corrosion tech I've had hundreds of people tell me their neighbors boat or shore power is the problem. While theoretically possible, I've never seen it. Every single case I've investigated, the victim boat has been the master of it's own disaster.

Very hard to tell from photos but if that is "stray current" you'd better take a hard look at your shaft, propeller and rudder stock. I've seen them destroyed in a matter of days.

You can go to ABYCinc.org to find a Certified Marine Corrosion tech or buy one of these to plug into your multi-tester and track down the issue. There are others on the market but this one comes with a pretty straight forward booklet that tells you how to do it. https://www.boatzincs.com/corrosion-...electrode.html

PS. Don't hire anyone who uses the word "electrolysis", that simply cannot happen on a boat.

[Simi 60]

Originally Posted by boatpoker

As a retired Certified Marine Corrosion tech I've had hundreds of people tell me their neighbors boat or shore power is the problem. While theoretically possible, I've never seen it. Every single case I've investigated, the victim boat has been the master of it's own disaster.

Nice to know.

We are about to go into a marina for a bit
First time in 7 years and was worried. about stray current from others

[Don C L]

Originally Posted by boatpoker

As a retired Certified Marine Corrosion tech I've had hundreds of people tell me their neighbors boat or shore power is the problem. While theoretically possible, I've never seen it. Every single case I've investigated, the victim boat has been the master of it's own disaster.

Very hard to tell from photos but if that is "stray current" you'd better take a hard look at your shaft, propeller and rudder stock. I've seen them destroyed in a matter of days.

You can go to ABYCinc.org to find a Certified Marine Corrosion tech or buy one of these to plug into your multi-tester and track down the issue. There are others on the market but this one comes with a pretty straight forward booklet that tells you how to do it. https://www.boatzincs.com/corrosion-...electrode.html

PS. Don't hire anyone who uses the word "electrolysis", that simply cannot happen on a boat.

This is a great tip, thanks for that. Perhaps something else to check is whether you have added any electronics lately and how they are grounded?

[smac999]

Originally Posted by boatpoker

As a retired Certified Marine Corrosion tech I've had hundreds of people tell me their neighbors boat or shore power is the problem. While theoretically possible, I've never seen it. Every single case I've investigated, the victim boat has been the master of it's own disaster.
.

I have… Problem could be your boat or another. Could be ac or dc current. Both cause damage. But hard to check with your boat out of water. Best to put it back in the same slip to test.

[boatpoker]

Originally Posted by smac999

I have… Problem could be your boat or another. Could be ac or dc current. Both cause damage. But hard to check with your boat out of water. Best to put it back in the same slip to test.

AC can cause stray current corrosion and does in pipelines ... a totally different environment and life expectancy. In salt or fresh water the process is so slow you would not notice it in your nor your kids and probably your grand kids lifetimes.

[Fishspearit]

Wish I were closer to Panama City, I'm an ABYC Corrosion and Electrical tech and could help you but I'm about 8 hours away.

It will take more than just those pictures to figure out what is going on. I suspect galvanic corrosion. Stray current corrosion is FAST, if that happened in a matter of days than I would suspect SC, but if it's taken months...

A knowledgeable person needs to look at your wiring/bonding system and check your fittings with a reference electrode when you're back in the water.

[fstbttms]

Originally Posted by Fishspearit

I suspect galvanic corrosion.

I suspect that you don’t understand what galvanic corrosion is. Perhaps you can elaborate upon which two dissimilar metals are in contact with each other in this situation.

[Fishspearit]

Originally Posted by fstbttms

Perhaps you can elaborate upon which two dissimilar metals are in contact with each other in this situation.

I haven't been in the boat, I have no idea what is bonded to the keel bolts in it. 14 years is plenty of time for owners to do all kinds of strange partial bonding. That's why these things need in person inspection, not diagnosis from a photo.

The metals don't have to be in physical contact for galvanic corrosion, just electrical contact and in the presence of an electrolytic solution.

[fstbttms]

Originally Posted by Fishspearit

I haven't been in the boat, I have no idea what is bonded to the keel bolts in it. 14 years is plenty of time for owners to do all kinds of strange partial bonding. That's why these things need in person inspection, not diagnosis from a photo.

The metals don't have to be in physical contact for galvanic corrosion, just electrical contact and in the presence of an electrolytic solution.

This is rust. It is an iron keel that is rusting. It is not galvanic corrosion. It is not electrolytic corrosion. It is rust.

[boatpoker]

Originally Posted by Fishspearit

I haven't been in the boat, I have no idea what is bonded to the keel bolts in it. 14 years is plenty of time for owners to do all kinds of strange partial bonding. That's why these things need in person inspection, not diagnosis from a photo.

The metals don't have to be in physical contact for galvanic corrosion, just electrical contact and in the presence of an electrolytic solution.

Please describe how the current moves (+ & -) without a physical contact.
One path is through the electrolyte. I don't understand how the other path could occur without a physical/electrical path.

[Fishspearit]

Originally Posted by boatpoker

Please describe how the current moves (+ & -) without a physical contact.
One path is through the electrolyte. I don't understand how the other path could occur without a physical/electrical path.

Re-read my quote that you posted. I said it needs electrical contact, not necessarily physical contact. That seems to be the same thing you are saying.

It's why we use galvanic isolators. You're boat is not in physical contact with the boat next to it, but they 'can' be in electrical contact through the AC grounding conductor.

I should ask though since you are an experienced surveyor, do you agree with fstbottoms that it is simple corrosion that occurred in "a few months"?