LOVING YOUR BOAT TO DEATH – Electro-chemical Destruction / Underwater Rot

LOVING YOUR BOAT TO DEATH – Electro-chemical Destruction / Underwater Rot

The subject of electrochemical destruction and wooden boats has been covered extensively on WW – in fact the Chris McMullen articles are the most referenced stories on the site. At the end of todays story I have listed links to these stories.

Today thanks to Chris McMullen and Baden Pascoe we get to share an article they penned for the 2023 Mahurangi Cruising Club Year Book*, this article succinctly backgrounds the topic and suggests what as a wooden boat owner you should be looking out for and what to do to protect your wooden boat. READ IT. But if you are lazy – let me spell stout for you – DO NOT FIT ANODES or BOND YOUR WOODEN BOAT.

Note: PDF version below for easier viewing for the visually challenged – i.e. most of us 🙂

(*Article reproduction with the permission of the Mahurangi Cruising Club©️)






The Continuing Issue of Electrochemical Damage To Our Wooden Boats – Lady Ellen


The Continuing Issue of Electrochemical Damage To Our Wooden Boats

 I recently received an update from Bruce Mitchinson on the restoration work underway on his 36’,  McGeady built (c.1950) classic launch, Lady Ellen. Unfortunately the old lady has a been struck with a dose of electrolysis.

You can see when the secondary shaft log was removed, electrolysis had destroyed the planking around the plate fastenings. The same problem around the main shaft log, and strut fixings, through structural members, which were all bonded together. The affected timber has been removed and new kauri blocks glued in and around the shaft log, keel bolts and floors.

The to-do list this week includes laminating up pilularis frames insitu, to replace the 15 broken, or electrolysis affected members that have been removed.This will complete the inside structural work, below the waterline, that had been put off until things dried out enough.

Other work has seen the old fuel tank removed and a clean up around the bilge in the engine bay Following this Bruce will be working his way forward with stripping and refastening on the outside of the hull.

The shaft, prop and drive couplings have gone down to Whangaparoa for adjustment, set up, and balancing.

Hats off to Bruce for doing the best of Lady Ellen. To read more on this problem, the causes & remedies – visit Chris McMullen’s WW story – link below. Its the most referenced story on WW.


Read more on her past & current restoration work at the links below.



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.