Galvanic action

[ChristopherShaw]

When I bought my 1944 Admiralty MFV the surveyor recomended various bonding of hull fittings and connection to anodes. Four years later there's been a gradual build up of salt like crystals around the three under the heads and I think some deterioration of the 70 year old larch around the fittings. The fittings are salt water in, foul water out from the loo and grey water out from the washbasin. On the other side of the (wooden) hull the corresponding hull fittings under the galley are fine having not been bonded. Where the problem lies they are bronze hull fittings with ss sea cocks screwed in and the bonding (done by the seller) goes from each bronze hull fitting to a single s/steel valve and then one wire to the anode. It seems to me that (all the other connections to the fittings being plastic) this has actually created a galvanic cell which didn't exist before. Any ideas would be welcome.

 

[savageseadog]

Which goes to show that there is no easy solution to these problems. My own view is that small fittings under the waterline such as skin fittings are best left electrically floating ie not bonded. The prop shaft and prop are best directly protected as the engine is connected to the battery negative and there is often a mixture of metals as well. Iron keels are best off with their own anode as well.
These are my own opinions and the technology is difficult and not totally foolproof. There is no, one, solution.

 

[chrisross]

I agree with Christopher Shaw. I had a 1965 Westerly 30 with no anodes at all and all the fittings seemed fine. The MG Duff surveyor advised fitting anodes whcih I did (But a think some anodes have "MG Duff" cast on them) By joining the fitting and anode a cell is created with the zinc wasting. I only fitted the anodic protection to the propellor and engine.

 

[Gordonmc]

I have always gone on the theory that bonding results in acidification of the wood fibre content around a fitting. For that reason I have fitted anodes to galvanised mild steel items, like the rudder pintles and bilge plates but left through-hull bronze alone.
There is one large anode wired to the engine and nothing else. I am thinking of removing the bonding and using a pear anode to hang over the side, earthed to the engine.
I don't think it does a wood hull much good to be part of a galvantic circuit, especially in a marina environment with lots of stray current.

 

[johnlilley]

Hi There
anodes and timber boats can be a very destructive setup, even more so if they are wired to stern tubes, rudder tubes and skin fittings as, as they work the currents produced cause chemical changes in the solution surrounding the metal parts being protected, these chemicals destroy the timber, the first sign being a sludgy crud similar to battery terminal furring around the anode fastenings internally and any internal damp, protected metal assembly. Anywhere this crud is visible you can be certain that the timber is being destroyed. Occasionally the damage can be so severe that complete sections of deadwood, planking and associated structure have to be replaced. Occasionally many thousands of pounds because of incorrectly given advice by some.
I would suggest removing the wiring, however the final choice is up to you!!!!

My own web site/s have further info, but just recently I have noted two extensive areas of damage of two separate timber vessels, one repair being quoted at over £20,000

John Lilley

 

[Mirelle]

Good!

A comment from a surveyor, which is just what we need.

Needless to say, I agree.

 

[fisherman]

[ QUOTE ]
The prop shaft and prop are best directly protected as the engine is connected to the battery negative

[/ QUOTE ]

It is a cheap and simple mod to fit insulated return on starter and alternator. Lucas CAV can do it. Saves a lot of damage. You would need dipole senders as well.

 

[Mirelle]

I absolutely agree.

Reduces risks from stray current electrolysis.

 

[ChristopherShaw]

Many thank chaps, that's very helpful. I did disconnect the bonding a couple of weeks ago but that seems to make things worse and I imagine that it's becuase the anode is only a few inches away from the fittings and there will be a galvanic flow through the water. I guess the short term solution is to re-connect and then, when she's out of the water, remove the anode and do away with the bonding. I'll see if I'm brave enough!