anodes on wooden yacht ??

[John O Sullivan]

Hello all, I am new to this site and in the last
2 years have restored a 50 foot Berthon boat co
yacht built in 1949. She is built with Mahogany
on oak frames over a lead keel. Unfortunitly I
have electrolysis with the iorn floors and bolts
that were mild steel at a guess. I have replaced
these with silicon bronze bolts and screws. I also
had to replace 3 oak ribs. To my surprize salt
is building up again on the floors. I have added
two anodes to what was on her to give me a total of 4
and wired all to engine floors etc. I checked with
a meter and have very good contacts.
I have looked back over 30 topics on your site but
could not find advice on this subject...
What is the advice on anodes.

thanks,
John.

[Ian McColgin]

Well, at least you'll save money on batteries.

Seriously, did someone advise you to mix bronze and ferrous metals? And if they did, do they have a way to prevent what appears to be inevitable electrolysis?

I think you have a very serious problem here that may amount to redoing much of what you've done. Tell us more.

[Andrew Craig-Bennett]

Hello, John. Have you tried doing a "search" (button at top left of this web page, above) on "anodes" "electrolysis" and "bonding"?

Here's a sample:

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=003125

plenty more in there!

As I said on the YBW site, I am hesitant to give advice, other than "find a really good wooden boat surveyor!" but, if you will keep in mind that I am not a professional, this is the summary of my experiences:

The late Peter Brown, a really good designer and surveyor, used to recommend bronze bolts and screws on galvanised mild steel fittings above the waterline; he did not recommend this below the waterline. Below the waterline he went with all bronze or all steel.

I have a distinct impression that several Solent yards of high repute, including Moodys and the Berthon, used to use bronze bolts on iron strap floors, certainly in the 30's and I think in the 40's and early 50's as well, and this was found to be a Bad Thing. I suspect that the iron floor bolts you have taken out were perhaps not original, but may have been replacements for bronze!

Back in the old editions of Wooden Boat I recall a truly horrific story about electrolytic action on a Berthon-built boat - a Gauntlet. In fact I fancy the boat was the name boat of the class. She had lived in the States for several years in warm water and had had a bus bar bonding all metal in her installed with copious zinc sacrificial anodes bonded to that. The result was awful because the alkalis and acids produced as the resulting battery fizzed away ate into the timber. It's in the back issues somewhere.

You may find that she is not all mahogany planked but has some lower strakes of teak. The reason for doing this (it was a very common practice at the good East Coast yards, like Tucker Brown, who built a lot of Buchanan boats) is threefold; teak is a tougher wood when saturated than mahogany, it is heavier (so best kept low) and it is less affected by any electrolytic action involving the floors and bolts!

By the way, I think you are the owner of a very distinguished and beautiful ocean racer of her day - don't hesitate to say so, here!

[Bob Cleek]

Not that you want to mix dissimilar metals if you can avoid it, BUT... buck bet it's the "bonding" and all those anodes you've go on there. Sounds like you have wired up one big battery! A bronze keel bolt going through an iron floor shouldn't cause THAT much problem. Remember that to have an electrolysis problem you have to have two dissimilar metals (eg: bronze and iron) IN AN ELECTROLYTE. Salt water is the electrolyte we are talking about here. Unless your bilge is perpetually full of salt water imersing the floors and bolts, the electrolysis should be negligible. If you have "salt" or white alkali powder growing around metal fittings, you are probably "cooking" the wood with an "active" current rather than a passive electrolytic action. For openers, I'd break the "bonding" totally. Get rid of it. All it does is tie all the metal in your boat together so it ALL gets eaten up. Now, I know that the "sacrificial" zinc anodes are supposed to go first, but if you put too many on, or too much of a mass of zinc, to be more exact, you will end up reversing the process. Use zincs most sparingly. Usually, nothing more is required than one on the prop shaft. And, as said, follow the good advice above and have a qualified surveyor look at it. (There is also the possibility that you have a wiring problem aboard, sending current through all that "bonding."... or a hot stray current in your harbor. You got any grounded shore power lines coming aboard that are tied into all that "bonding?" Think about it...)

[Andrew Craig-Bennett]

My guess is the same as Bob's.

My boat, copper and bronze fastened teak on oak, iron keel, iron and steel strap floors, iron and steel bolts, has negligible electrolytic or galvanic action, these days. That's since I "got religion" about battery isolating switches, re-wired her, very carefully, and removed the zinc anodes.

[John O Sullivan]

Thank you for your help. I plan removing the anodes in the spring. Depending on what I find
I may remove the bronze bolts and replace with coach bolts. I did coat the bronze bolts in a black mastic called wurth. think that is what it is called. Will keep ye posted on developments.

happy new year.
John. http://www.imagestation.com/album/?id=4288167351