Want to see what electrolysis does to a wooden boat?


 What Is Electrolysis?
I have published Chris McMullen’s comments below for 3 reasons:
1. Out of the blue, today I was sent the above 2 photos by a woody owner who has just discovered they have a time bomb ticking away. Bomb is a good analogy to use as the green wires in the bottom photo are the detonator 😦
2. The subject of electrolysis & wooden boats is topical at the moment
3. I’m passionate about saving our old wooden ladies.

You can read more on the subject here https://waitematawoodys.com/2016/04/28/electro-chemical-damage-in-wooden-boats/
To quote the dictionary – Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water. Electrolysis of salt water or Brine – electrolysis turns NaCl + H2O in electrolysis will produce separated hydrogen gas, chlorine gas and sodium hydroxide*. *Sodium Hydroxide is also called Caustic Soda. It is used for pulping wood in the paper industry and on a boat it forms around any anode protected metal (Cathode) and softens the wood.
Lets check again in the dictionary – “The cause of Electrolysis?”
Electrolysis is due to an electric current being passed through the water or Brine. Surely, the way to prevent electrolysis on a wood boat is by eliminating any electric current passing through the wet wood.
There are two sources of electrical current on most boats.
1. The DC battery used for starting the engine and services. Stray currents are common,(can be very damaging) and hard to find on wooden boats. Any connected dissimilar underwater metals including anodes will create a galvanic current 24 hours a day. There should be no connected dissimilar metals underwater and keep the ships DC system isolated from any metal connected to the sea.
2. Bonding makes a circuit and encourages stray and galvanic currents; the result will be electrolysis and degradation of the wood around metal hardware.
Protecting marine metals (bronze or copper) with an anode is pointless and sets up a current and causes electrolysis that again produces sodium hydroxide that pulps the timber in a wooden hull. If you have brass or manganese bronze underwater, an anode may help protect the metal but set up a galvanic current with resultant damage to the wood surrounding the cathode or protected metal.      

See on Google – graphic descriptions of exactly what happens on our boats if we create an anode and a cathode. Chlorine gas is produced at the anode and hydrogen gas at the cathode.


Whether we like it or not, the brine around any cathode or protected metal converts to sodium hydroxide (caustic soda) and this is fatal to a wooden boat.

The solution is very simple – you should not use anodes on a wooden boat.
Anodes are necessary / desirable on steel structures where there is no wood. To use them on a wooden boat is a relatively new idea or myth designed as a solution looking for a problem. On wooden boats it has been proved worldwide to be a disaster but some in the NZ marine industry refuse to admit they have been wrong and continue to promote this profitable business.

The Logan’s, Baileys and Colin Wild never used anodes or bonding and neither should anyone who cares for their wooden boat.

 Read http://mgduff.co.uk/support/knowledge-base/questions/what-is-electrochemical-decay-in-wooden-vessels  

If you would like some more technical evidence read. http://www.mcclavemarine.com/text%20pdfs/Corrosion.and.Corrosion.Protection.Wooden.Boats.pdf

P.S. Chris would like to advise that he has had no input or involvement in any organised discussions on the topic of electrolysis & wooden boats.

13 thoughts on “Want to see what electrolysis does to a wooden boat?

  1. Pingback: LOVING YOUR BOAT TO DEATH – Electro-chemical Destruction / Underwater Rot | waitematawoodys.com #1 for classic wooden boat stories, info, advice & news – updated daily

  2. My uncle has a large 1940’s wooden launch, it has never had anodes and no corrosion of metals. Also no delignification in sight.


  3. sounds like you should be looking for stray current, either poz or neg. bronze and stainless are very close on the galvanic scale and something must be setting off the fizz. Thousands of boats have props and shafts co-existing with no fizz.


  4. A bronze prop on a s/s shaft are 2 different metals, so some galvanic current has to exist! Same current as fitting a zinc anode to the shaft. So much out there “fit an anode..” another the opposite. Trouble is, no one makes 3 bladed props for in board engines in stainless steel, closest is kiwiprop which folds, not fixed, so everyone like me with a 2GM Yanmar is now stuck with bronze. Our first prop all but disolved. Now with a one of Bobs anodes on it, the anode disolves but of course fizzing is now occuring around the inboard propshaft bronze collar so I have now been told to earth the prop shaft through the flexi coupling to the gearbox flange! Hang on, everyone is saying dont bond!? Dont zinc shafts. So its probably cheaper to have the prop leach out than the shaft log collar!? Theres no end to this!??


  5. Thank. you Chris and Murray for your reply and thus your warning to us ..classic and modern classic.


  6. Simon I can confirm that “modern” glued double diagonal and glassed construction has all the same issues as Chris has pointed out, having seen two Townsons and a Stewart where the well meaning owners or their advisers had bonded all fittings and caused a rip roaring battery -where previously the boat had been fine -and was again once disconnected.


  7. Steve, I’m sure it was a fantastic presentation but it upsets me that only 11 people attended, there are over 200 wooden classic’s in the CYA fleet & probably 3x this who are not members. Apathy is alive & well in the wooden boating movement.
    Image an invite to a function that would help reduce/stop cancer – go would need to hire Eden Park 🙂
    Hopefully it was lack of awareness re the event & or the fee of $50, rather than apathy 😉
    As an aside – Chris McMullen’s post on ww re this issue is the single highest viewed story on the ww site.

    Alan H


  8. Alan H – Note : The below refers to a function last night organized by the NZTBBS.

    A fantastic presentation last night by Colin Pawson on behalf of the New Zealand Traditional Boat Building School. The 11 attendees went away with a thorough understanding of the science and theory of electrolysis on old wooden boats including some active demonstrations. The conclusion confirmed our long held view that generally speaking our classics don’t require bonding or zinc and explained the reasons why and also the potential damage caused by zinc. The presentation also covered such topics as stray electrical leaks from old wiring and tired electrical equipment and the pitfalls and problems associated with connecting to shore power at a marina. A great night and the first in what we intend to be a series of talks on useful topics for boaties.

    Steve Cranch


  9. A good question. You may think your modern construction is dry but around all the metal through hull fittings and stern and rudder tube will most likely be wet. If these metals are bonded to an anode or/and the electrical system you will make Sodium Hydroxide around the cathode or protected metal. If the wood is sealed perfectly with resin you may get away with it. Paint is useless as Caustic Soda is an effective Paint remover.
    I have seen Townson boats with these problems so be aware.


  10. i have read that this wood electrolysis refers to planked hulls only,. the article suggested that the modern say 2 skin glued wooden hulls (ala townson ) would not be prone to this wood disintergration. is this correct .?


  11. No anodes on Lucinda. All old bronze and new AB2, only ss is new 316 rudder. Isolated prop shaft from engine, isolated battery negative from engine.


  12. That’s serious. Recently returned Ngatira to the water without an anode. I will be watching with an eagle eye the results.


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