Electrolysis

[Burge]

Hi,

I am interested in purchasing a carvel plank 40ft yacht but have recently found out that there is some instances of damage to the hull being caused by electrolysis and would like to know more about the subject including how easy it is to fix the problem and what the scope of work is going to be including cost before I put an expert on board to have a look.

The boat is over 40 years old so I am guessing this problem has only developed recently and think it might be related to the engine recently being replaced as the problem areas are close to the engine. There are several internal hull fittings near the engine which appear to have problems as the paint inside and outside of the hull has stripped including antifoul and there is build up of corrosion on the fittings, On one fitting in particular the adjoining planks appear to have been fried or rotted out and are still hard under a hammer but seem to have become permeable to sea water and are acting as a sponge in addition a section of connecting timber frame is rotted and can be crumbled by hand.

When I viewed the boat out of the water there were areas of major weed growth which corresponded to the problem areas on the inside.

A marine sparky has had a go at the problem and has installed earthing cables and carried out protection test with apparently good results but something is still happening.

My understanding is that there are two possibilities either galvanic corrosion due to differing nobility metals being linked or insufficient anode protection or stray current. If its galvanic corrosion is it just a case of removing unnecessary link wires and beefing up anodes and if its stray current is it just case of finding the short and fixing the problem?

I would appreciate any advice on the subject, I have attached a photo showing patch of outside hull which had major growth top left and the other photos show other areas which had a lot of growth and loss of paint layers etc.

Thanks in advance.

[Mirar]

Hi there, I had a wood vessel that we launched new in the late 70's and cruised extensively for 3 decades so we saw it all as far as issues. I think what you may be seeing is hydrolysis, a chemical reaction with the wood fibres and the various metals in the hull and salt water. When you mentioned that someone has had a go at bonding all the thru-hulls, my senses perked up. I recently had someone call me about the same issue and they determined that most of the signs of wood deteriation began with the bonding.
Google "hydrolysis in wood boats" for lots of info. We found that by painting on some vinegar then after that treating the wood with a pine tar and linseed oil mix it seemed to stop it. We also disconnected our bonding system.
Here is one link for you to start with. https://books.google.ca/books?id=39_...0boats&f=false.
Greg

[Lepke]

I'm 67 and been around wood boats and ships a long time. I was a shipwright, etc. You bond metals together so they don't react with each other when in the water. Usually each metal object has it's own zinc. The only times I found wood damage around a fitting from electrolysis was from improper wiring giving off higher current. Usually some radio wired backwards that passed current thru even when turned off. Enough so it would drain a battery bank in a few days if not on a charger. I saw a 36" prop that wasted it's blades in a month.
Your pictures look to me like a paint bond failure. It didn't stick well to the old paint and left areas for colonization. Once there is no paint, marine organisms are entering the wood. The paint appears to be thick and probably for many years the bottom was just washed between coats of bottom paint. It probably needed a good sanding. On commercial wood boats, we sanded between coats and usually stripped to bare wood about every 10 years. And before the EPA we had better paint and wood preservatives.
You're looking at a 40 year old boat. It's going to have some rot, somewhere. The only perfect 40 year old wood boats just went thru a major rebuild and haven't hit the water yet. Rot organisms travels thru wood and can contaminate other woods they touch. There are products, I don't use, that can be poured or injected into soft wood to make it hard again. They don't restore the strength. You deal with it by cutting out the rot and replacing the wood.
Should you buy this boat, the old way of extending the life of wood boats was to keep rock salt loose in the bilges. I still do. Salt is a preservative. Also, boats and ship built before 1930 usually had salt boxes built into the sides, between the ribs, right under the deck. On a properly curved deck, water that collected under the deck or dripped thru the deck ran to the sides and thru the salt box and down the sides preserving the ribs, planks and bilge. Don't dry out the hull.
My boat will be 73 years old soon. It had poor care for 20 years before I bought it, but had a copper sheathed bottom, and lived in salt water. The hull is in excellent shape. There's one sister rib and almost all the original planking. Topside is another story.

[Terra Nova]

RUN away!

[Burge]

Hi Greg,


Thanks very much for your post it appears Hydrolysis fits the bill. I have done a bit of research and the description of the cellulose fibre break down in the timber appears to be an exact match for the porous planks and also the frame in contact which has completely shredded.


Its a real shame as I love the boat and have been after it for about 5 years so I would like to know if this condition just affects the immediate areas around the fittings or can the build up of high alkaline water affect anything it comes in to contact with i.e. the whole bilge?


Also I suppose its a three stage problem as in you have to fix the electrolytic problem to begin with either the cathodic system or stray current and then treat the Hydrolysis and then repair the damage its done to the timber.


My only worry would be what if this is going on in areas you can't access from the inside of the boat like behind tanks?


Anthony

[Burge]

Thanks Lepke,


I appreciate the benefit for your considerable experience.


By the sound of it the bonding which has been installed the hulls fittings is adding to the problem.


Faced with these issues would you run away from this boat or can these problems be fixed and further treatment prevent from happening in the future?


Anthony

[Terra Nova]

Originally Posted by Burge

...I am interested in purchasing a carvel plank 40ft yacht... over 40 years old...

Originally Posted by Burge

...I love the boat and have been after it for about 5 years...
My only worry would be what if this is going on in areas you can't access from the inside of the boat like behind tanks? ...

Well, that might change the complexion of things. As long as you know what you're getting into.

The affected planks can be individually replaced. Same with any sick hardware. Access behind tanks (which probably need replacing) is easy--remove a plank or 2. But a 40-year-old wooden yacht is ready for a major refit, the cost for which could exceed the price of a new boat, if you had to hire it out.