Electrolysis - or something else?

Hello All:

Please see the attached pics and cast your opinion. I appear to have some pock markings on various places of our boat (port lead car track aft end, but not on starboard, boom, base of mast). Is this electrolysis or something else? I have asked some of the local people here in St. Thomas and opinions vary.

What type of a professional would I approach for help with diagnosis and treatment? Marine electrician, general handyman, rigger? Of note, our boat took a near lightening strike last September and sustained significant damage to navagation and electrical equipment. We replaced a lot of our equipment.

Initially, I thought this might be just 'wear and tear' on the boat, but now I am not so sure.

Thoughts or comments from Europe?

Cheers,

P Milo

s/v The Last of the Normal People

Swan 47/048

Starboard aft end of lead car with no damage.

Milo

Boom Vang with pock markings.

Milo

Base of mast.

Milo

Base of mast.

Milo,

I think it is corrosion.

I cleaned all aluminium parts on the boat mast, boom, blocks, toothrail etc. with bleacher, degraeser etc. several times to make the eloxed aluminium clean as possible.

After this procedure I used german brand "nanocoat cleaner" and all parts are like new. You have to make the sealing with nanocoat cleaner several times.

(www.nanocoat.de). It is a new technology and more better than all other products,

fair winds

Jan

Swan8/85 "Kalliope"

Hello Jan:

I am always impressed and thankful that Europeans have such a strong command of the English language and often speak a third and fourth language. Meanwhile, I speak only English....well, a little bit of jive, too!  :)

I hope I do not offend you by asking for clarification of your choice of words. In particular, 'corrosion'. As I read your helpful response, the implication was that corrosion was different to electrolysis. Do you understand corrosion and electrolysis to be different? Is this particular metal on my boat prone to corrosion and that the cleaning process you described a means of stopping the corrosion?

The website you hyperlinked looks like a great product (Nanocoat). Unfortunately, the website is in German. I am trying to find an equivalent product over here (and in English). It may be easier for me to sail over and buy some.

I look forward to your response.

Milo

Dear all

I would suggest the first picture shows the effects of some very strong chemicals, maybe a teak conditioner, which has destroyed the anodizing layer locally, and left the aluminum surface bare. White aluminum oxide will then form on the surface. The unprotected metal corrodes very slowly due to the presense of seawater.

Another type of corrosion is denoted galvanic and may occur for example in the toe rail around the stainless bolts. The nobler metal is stainless, and when both are immersed in seawater the aluminum will work as a sacrificial anode, and is eaten away while the stainless remains unchanged. If the two metals are not  in electrical contact with each other galvanic corrosion does not occur. For this reason newer Swans have plastic washers under the toe rail bolts. These washers can be bought from Nautor spareparts, but they are intended for Allen head bolts and not slot head bolts, the geometry is different. There is another way to prevent galvanic corrosion between the two metals - introduce a third one which is less noble than aluminium, for example zinc. By putting in zinc anodes for each bolt the aluminium will not suffer but the zincs.

The third main group of corrosion is called electrolytic, and is caused by leaks in the electrical system om board. The effects may be reversed or same as the galvanic depending on which one is connected to the positive or negative pole.

I stop here in fear of the time limit expiring

Lars

Lars,

Thanks for adding some clarity to "corrosion"

Now, would your opinion of the first picture change, with the additional information that at the time we noted the corrosion, the rail had been in and out of the water for hours, and when we pulled out a voltmeter, we noted 12v differential b/t toe rail and lead car track.  couldn't find any obvious electrical leak, but voltage disappeared when we turned off one of the breakers on the main control board (theoretically, none of the electrical work recently done on the boat had involved anything on that circuit)

When we checked for voltage later between the two, with and without the breaker on, it was no longer there.

SOOOOO..... if electrolysis--how do we track down the source??

forgive any misuse of electrical terms--clearly this is not my area of expertise!!

thanks for any help

jill

Jill,
a 12V difference between toe rail and lead car track is quite bad news indeed.
Next time it happens, you should note which is the positive part; all metal parts of the boat are supposed to be connected to the negative terminal of the battery so a positive voltage will narrow the search of the culprit and make the solution easier.

Daniel

Dear Jill