electrolytic corrosion

[splax]

I hauled out to paint and have discovered extensive pitting on the iron keel. I had remarked to those pulling the boat how good the shaft zinc looked. It seems the keel is used as the negative bus. Any suggestions for a more appropriate arrangement to stop the keel corrosion?

 

[sail sfbay]

My guess is the keel barrier coat failed. Same thing happened to my Hunter 46 due to lack of maintenance by the seller. Yard sanded the entire keel to remove corrosion products and pitting to bare metal, then applied 5-7 coats of epoxy barrier cost then antifouling paint.

 

[gfrazzle]

Splax,
I'm no expert but here's what I have learned from my experience:

"Sacrificial" zincs are on the bottom of the nobility scale so if installed correctly should be the first to go. The fact that yours is in good condition would indicate that that is not the case. Building a protective system is a complicated issue (Nigel Calder's Boatowner's Mechanical and Electrical Manual has a fairly extensive chapter on this).

I would recommend hiring a marine electrician with a thorough knowledge of galvanic corrosion to check your boat.
I had the same issue that destroyed my 18" 3 blade bronze prop in a couple of weeks. After it was finally cured, I bought a galvanic corrosion meter/ tester and now check my boat monthly. Marine Digital Corrosion Tester - Seaguard International
If you decide to buy this tester, spend the extra for the Pro model or you will be replacing the anode later.

Good Luck!

 

[JamesG161]

Any suggestions for a more appropriate arrangement to stop the keel corrosion?

You cannot mount a Zinc big enough to stop galvanic corrosion on your keel.

You must barrier coat it to prevent the galvanic coupling, but it should still remain the grounding on your boat.

Grounding and Galvanic Corrosion are different things.
Jim...

 

[sail sfbay]

You might the following article helpful in understanding galvanic corrosion of a lead keel and repair plan . My two cents..........maintain an adequate barrier coating between the keel and high copper antifouling paint, keep the keel clean and regularly inspect the antifouling paint over it for signs of paint thinning.

Keels: Minor Maintenance and Repair - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

 

[splax]

You might the following article helpful in understanding galvanic corrosion of a lead keel and repair plan . My two cents..........maintain an adequate barrier coating between the keel and high copper antifouling paint, keep the keel clean and regularly inspect the antifouling paint over it for signs of paint thinning.

Keels: Minor Maintenance and Repair - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com

the 34 has an iron keel

 

[sail sfbay]

Lead............then you might find the last post in this thread helpful.............the owner installed anodes on each side of the keel to mitigate corrosion.

Keel Electrolysis on Bavaria Vision 46

Keel Electrolysis on Bavaria Vision 46

bavariayacht.org

 

[fstbttms]

I hauled out to paint and have discovered extensive pitting on the iron keel.

You sure what you were looking at wasn't simple oxidation aka. rust?