Ian Mabbett Talk – Marine Corrosion
Many thanks to our fellow Club member and Berth Holder Professor Ian Mabbett who gave a very informative presentation on the subject of Corrosion and the use of Galvanic Isolators at the most recent Berth Holders SGM held in the Clubhouse on the 19th of June. Ian’s presentation drew forth a number of questions from the audience who were very appreciative of the information provided.
A truly staggering statistic is that the annual global cost of corrosion is $2.5 trillion, equivalent to roughly 3.4% of the world’s gross domestic product. Implementing corrosion prevention best practices could result in savings of 15-35% of that cost, or $375-$875 billion. Whilst there is little we can do individually to help address this global problem, we can do things to help reduce the effect of corrosion on our vessels. Even carbon fibre boats are not immune as carbon is a conductor. Corrosion is inevitable for all vessels, but we can help stem its advance. Galvanic isolators can protect vessels which are connected to shore power; their use isn’t mandatory within SYSAC Marina, but please be aware that this can be a mandatory requirement elsewhere in other marinas. If your vessel doesn’t already have a galvanic isolator fitted, a simple ‘plug in’ device to be attached to your short power lead can cost less than £100.
As for the Salinity levels in SYSAC Marina, in all probability the conditions will be that of medium salinity, in which case Aluminium Anodes will work best. But please be aware that if you change location, the salinity levels may alter.
What about salinity?
1. Saltwater (High Salinity)
- Zinc anodes are traditionally used in saltwater, offering reliable protection.
- Aluminium anodes are becoming more popular because they last longer and provide better efficiency.
- Best choice: Aluminium or Zinc, depending on longevity and cost considerations.
2. Brackish Water (Medium Salinity)
- Aluminium anodes work well in mixed salinity conditions.
- Magnesium anodes may be too reactive, leading to excessive wear.
- Best choice: Aluminium, as it balances protection without degrading too quickly.
3. Freshwater (Low Salinity)
- Magnesium anodes are ideal because they have a higher electrochemical potential, making them
effective in low-conductivity environments. - Zinc and aluminium anodes are less effective in freshwater. Zinc may even passivate!
- Best choice: Magnesium, ensuring proper cathodic protection.
So …
- Corrosion is complex
- Galvanic corrosion will happen when we get dissimilar metals electrically connected and in contact with electrolyte
- We can try and isolate one or more parts of that system
- We can also protect with sacrificial anodes
- Stray current could spread through shore power earth
- Galvanic isolators or isolating transformers can stop this
- We can measure and monitor with Ag/AgCl reference electrodes
- But we slow rather than stop and we can still get localised effects