Anodes on a wooden boat

[gary3029]

Due to a post in another forum without much clarification thought I would try here. My boat was moored elsewhere and the anode was not coupled up...no problems. Have now moved boat and noted pitting a a ss nut. Have now connected the engine, shaft and keel to anode. However have been warned using anodes on wooden boat can cause problem to the wood. Can anyone fully explain why this is. Also how many wooden boat owners have anodes on their boat and have they had any problems.
Thanks

 

[john_morris_uk]

Pitting on a stainless nut is much more likely to be due to crevice corrosion.

The reason that anodes on wooden boats are often NOT suggested is that the electrolytic action induced by the anode destroys the wood in the areas immediately surrounding the anode. (I know as I had a wooden boat and had to replace a strake which had been destroyed by such action. I even have a bit of the strake which I kept and can post a picture if you want! From memory, its the alkali's caused by the electrotytic action which destroys the lignum in the wood fibres, but I'm raking the memory cells a bit for that info.)

Provided you use good quality bronze undewater fittings and don't connect them together electrically, most such fittings will survive many many years before they have to be replaced. Many boats don't have any of their seacocks connected to the cathodic protection, and they survive very well indeed.

 

[Rowana]

Go to the MG Duff website here -

http://www.mgduff.com/technical-downloads/

Then download the "Anode fitting instructions for Wooden & GRP hulled vessels"

That should tell you what you need to know.

 

[johnlilley]

Hi there, in my experience fitting an anode and then wiring it up to create a circuit on timber boats can, as you rightly note, cause extensive damage to the timber parts surrounding the metal parts it protects. As the circuit operates with the minimal currents created, the anode erodes as expected but due to concentrated chemicals which are formed around the connections, due to the forced eletrolysis, both at the anode and the wired & protected parts, particularly internal stern tubes the chemical effectively destroys the timber, The damage always occurs in the internal skin where, it seems to me, the lack of any flowing water to dilute the damaging chemicals results in concentrated solutions which can be evidenced in a white crud building up around the point of anode fastenings and wire termionation points on stern tubes & rudder tubes internally. If this crud is noticed, this is a sign that damage has already started to occur, and the only way to stop this damage is, in many cases, by cutting the wire and breaking the electrical connection. The stern deadwood is an expensive item to replace, and this would, in my opinion , take precedence over corroding props etc.

Washing the area with vinegar several times and then with clean fresh water will netralise the chemical, but in some cases the damage will have to be repaired. There is no guarantee that the lack of anode will be as serious on a good timber boat as some might fear, provided care is taken over isoltaing electrical equipment and batteries when not aboard.

This is in my experience, and others may well have differing views.

John Lilley

 

[Malcolm Warnes]

Alkali salts and wooden boats

Hi there, in my experience fitting an anode and then wiring it up to create a circuit on timber boats can, as you rightly note, cause extensive damage to the timber parts surrounding the metal parts it protects. As the circuit operates with the minimal currents created, the anode erodes as expected but due to concentrated chemicals which are formed around the connections, due to the forced eletrolysis, both at the anode and the wired & protected parts, particularly internal stern tubes the chemical effectively destroys the timber, The damage always occurs in the internal skin where, it seems to me, the lack of any flowing water to dilute the damaging chemicals results in concentrated solutions which can be evidenced in a white crud building up around the point of anode fastenings and wire termionation points on stern tubes & rudder tubes internally. If this crud is noticed, this is a sign that damage has already started to occur, and the only way to stop this damage is, in many cases, by cutting the wire and breaking the electrical connection. The stern deadwood is an expensive item to replace, and this would, in my opinion , take precedence over corroding props etc.

Washing the area with vinegar several times and then with clean fresh water will netralise the chemical, but in some cases the damage will have to be repaired. There is no guarantee that the lack of anode will be as serious on a good timber boat as some might fear, provided care is taken over isoltaing electrical equipment and batteries when not aboard.

This is in my experience, and others may well have differing views.

John Lilley

Hi, I have a similiar issue on my 40 year old 33ft wooden displacement launch (lapstrake construction) and your answer helps alot. However I have further questions and wonder what you can advise. My set up is bronze rudder stock, bronze propeller, bronze propeller skeg housing cutless bearing for SS propeller shaft, bronze tube at the top with cutless bearing, Ford diesel with Lees Marine Heat Exchanger driving hydraulic gearbox (with a heat exchanger for oil cooling linked to the raw water feed to engine). She has full keel and is in great condition. Currently I have an anode sitting on the keel just forward of the skeg and bonded to the skeg. In the bilge the skeg is wired to the rudder stock and to the bronze propeller tube. In the bilge I have alkali salts forming on the four bolts attaching skeg to keelson and likewise on the bolts in the rudder stock. The propeller tube does not have salts. The only other place where alkali salts are forming is on four bolts which are part of the gearbox heat exchanger unit so are in contact with raw water to engine. It appears to me that I should dump the anode. My questions are:
1) what about protection to the engine, it has several different metals and is contact with salt water, the electrolyte so will corrosion occur somewhere?
2) can you explain why wooden boats don't need anode protection given there are metals in electrical contact (the engine and components) and linked to the salt water via the heat exchanger cooling?
Appreciate any suggestions.