This has to be galvanic corrosion, correct?

[fstbttms]

Originally Posted by Fishspearit

...do you agree with fstbottoms that it is simple corrosion that occurred in "a few months"?

How long should it take for "simple corrosion" to occur?

[EmeraldCoastSailor]

In my mind my boat isn't bonded; it doesn't have ground wires to/from thru all the hulls and keel bolts. There is a ground wire from a keel bolt to the port chain plate that appears to me to be lightning director. I have a shallow bilge that stays 100% dry 99% of the time so no wet bilge pump wires. I have yellow wires from fuel tank to engine that appear to be static electricity dispersers.

As best I can tell it came on fast a few months ago. When I mentioned galvanic corrosion I was thinking it was a problem caused by stray current. Sorry if my wording wasn't precise.

Shaft and prop look good. Rudder is solid. I frequently don't even connect to shore power as my solar easily keeps the beer in the Engel frig cold and the house bank fully charged. I installed a galvanic isolator a long time ago.

I do have reason to suspect neighbor boats. When the marina installed new electrical system a few years ago, a few old boats were tripping the new interrupt that was installed. My understanding is that they removed the interrupt to solve the problem. I know for sure the boat next to me on starboard side was tripping the interrupt. The boat to port is a liveaboard mess that hasn't moved in a while and has much potential for trouble. I haven't asked if his boat was tripping the interrupt yet.

[boatpoker]

Originally Posted by Fishspearit

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'm now confused. previously you said physical contact was not required and now say there is physical contact through the shore ground. PS. less than 10% of the thousands I've surveyed have galvanic isolators.

Perhaps you'd like to re-word the comment below as a physical (path) contact is required in galvanic corrosion. ...

"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 EmeraldCoastSailor

I do have reason to suspect neighbor boats.

Your neighbors boat isn't causing your keel to rust.

[boatpoker]

Originally Posted by EmeraldCoastSailor

In my mind my boat isn't bonded; it doesn't have ground wires to/from thru all the hulls and keel bolts. There is a ground wire from a keel bolt to the port chain plate that appears to me to be lightning director. I have a shallow bilge that stays 100% dry 99% of the time so no wet bilge pump wires. I have yellow wires from fuel tank to engine that appear to be static electricity dispersers.

As best I can tell it came on fast a few months ago. When I mentioned galvanic corrosion I was thinking it was a problem caused by stray current. Sorry if my wording wasn't precise.

Shaft and prop look good. Rudder is solid. I frequently don't even connect to shore power as my solar easily keeps the beer in the Engel frig cold and the house bank fully charged. I installed a galvanic isolator a long time ago.

I do have reason to suspect neighbor boats. When the marina installed new electrical system a few years ago, a few old boats were tripping the new interrupt that was installed. My understanding is that they removed the interrupt to solve the problem. I know for sure the boat next to me on starboard side was tripping the interrupt. The boat to port is a liveaboard mess that hasn't moved in a while and has much potential for trouble. I haven't asked if his boat was tripping the interrupt yet.

No need to apologize, not everyone is educated on this stuff but the issue can tracked down if you buy the half cell I provided the link to. It's a terrific tool that every owner should have.

[Searles]

Will to bet that there is at least one or more ,so called earth wires on at least one keel bolt,maybe a chain plate to keel connection for so called lighting strike protection ,evedinceis there of a currant leek ,try to trace while the vsl is in the water .⛵️⚓️

[jamhass]

"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."

We were in a marina and found our zincs were eroding rather too fast. Boat for sale next slip over looked a bit dodgey, with a questionable electrical cable etc. Moved to a different slip, problem went away.

So, neighbor boats can well be an issue, as can faulty dock electrical systems.

[boatpoker]

Originally Posted by jamhass

"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."

We were in a marina and found our zincs were eroding rather too fast. Boat for sale next slip over looked a bit dodgey, with a questionable electrical cable etc. Moved to a different slip, problem went away.

So, neighbor boats can well be an issue, as can faulty dock electrical systems.

Did I not say it was possible ?

[T. Lee]

My suggestion would be to drop the keel, blast and rebarriercoat etc if you want to prevent reoccurrence. Not cheap but it will be good for a long time. the existing rust preventer has been compromised at the keel to hull joint. Joint flexing can crack coatings so perhaps your keel bolts have loosened allowing coating failure at the joint.

[OneBoatman]

I would first check with Beneteau to see if they recommend connecting anything other than what was connected at the factory to the keel bolts. I also see that the keel has an integral ground plate so that should be taking care of keeping your rigging at ground potential as for lighting strikes. You shouldn't need anything more. You should also take a look at the breakers which serve your spreader lights, comb light, anchor light, radar dome, and anything else powered aloft to be certain that you haven't developed a short inside the mast which might be making the keel behave anodic.

[gulfislandfred]

When I was with the Port of Port Townsend, Wa, we had a 'hot' dock. Boats on that dock had underwater metal corrosion problems, especially corroded propellers. This happened even when the boats were not connected to shore power.
We hired the best experts we could find, more than one. No one could figure it out, until a new guy in town suggested that we ask the power company to check the wiring on the transformers that supplied the docks.
Sure enough, three out of the four transformers had the legs of the 440V, where they split to 220V, synchronized, so they alternated in synch. The hot dock was out of synch, so there was a small pulse of current induced into the salt water around that dock.
The power company switched the wires to synch the fourth transformer, and the problem disappeared.
(The guy who suggested a look at the transformers had seen the problem and the fix in a different marina. He wasn't an expert. Just had the needed experience)

When I lived aboard in Seattle, in Lake Union, in 1969, there was really bad wiring on lots of docks and boats, but no corrosion of zincs or metal, because it was fresh water. It was so bad that a diver was electrocuted, and died, when he touched a hot wire underwater.

When I moved to Port Townsend, in salt water, there were many issues. Problems from individual boats, problems from nearby boats affecting other boats, problems from the marina electrical systems. Immerse a bunch of vessels in an electrolyte, hook most of them to shore power, and have owner maintenance; there will be stray current.

[kubota]

you mentioned a wire from a keel bolt to a chainplate.
this goes up your rig to the mast.
you most likely have a non isolated vhf antenna at top
of mast. this establishes a contact to the outer braid of coax. outer braid goes to vhf radio where it is common with electrical system negative which is common with engine shaft and prop to water sitting
in a conductive fluid (electrolyte) with your keel.
congrats. a complete electric circuit through your keel.

almost all boats display this path.
effects are varied depending on other wiring but
any current induced corrosion is particularly evident on iron keels.

degree of issue is measurable with a milliammeter and some skill. fix is isolate antenna with teflon washers or put a coaxial isolator inline.

something to check.

i can hear the flames starting already.
the topic of corrosion generates so much
bad information and inflamed "experts"
i just dont reply anymore, but i had an iron keel once and feel your pain.

i developed a procedure for measuring and locating stray current after looking at many boats over many years.. DM me if you are interested.

[Kit_L]

Some gold in this thread: bookmarked.

[Peeew]

Keep in mind that some of these French boats keep the Negative side of the AC system separate from the DC system. I’m that case it is easy for something to be installed with the neg side on the wrong buss. This can lead to DC current running to the AC side. This can eat metal pretty fast.

[kubota]

ps:
antenna issue is a vector for both galvanic
and stray current corrosion.

takes a few inexpensive instruments to figure which you have, or if like one poster said its strictly
chemical and just rust. without measurement
data, its all speculation.

good luck.
at least when you go aground it doesnt deform.