A question for timber boat owners re: grounding plates

I love this thread

Might as well jump in. A few points:

1. any professional in the field will be VERY cautious in saying anything about this because of liability concerns. Electrolysis is very clear in theory, but in practice more akin to witchcraft. In Theory, theory and practice are the same. In Practice, they're not. Every boat is different.

2. Someone already pointed out that wood in salt water can provide a current path, which deteriorates the wood. If you monitor it frequently, you can spot this before it's too late. the wood near metal fittings, throughulls, etc. will get white fuzzy. This is based on owning several wooden sail boats.

3. Excess sacrificial anodes can drive excess currents...not a good thing. I protect every piece of underwater metal with either an attached or a bonded sacrificial anode, but keep monitoring for signs of excess current leakage, now on a glass hull.

4. I agree that underwater plates are about grounding electronics and/or lightning strikes, not electrolysis, but they are subject to electrolysis like any other piece of metal.

Good luck.

I suspect the bolts sheared as the timber changed shape. I've never been a believer in the sintered bronze theory. However, stainless is less than ideal when continuously submerged, especially if the back side is trapping stagnant water, that's a recipe for crevice corrosion. If you must have a ground plate, for grounding and not corrosion purposes, it should be solid copper.

Ideally, timber vessels should not be bonded, as alkaline is produced around cathodes, i.e. bonded metals, which can lead to delignficiation. Better to isolate and protect under water metals individually for timber vessels.

MichaelD said:

Might as well jump in. A few points:

1. any professional in the field will be VERY cautious in saying anything about this because of liability concerns. Electrolysis is very clear in theory, but in practice more akin to witchcraft. In Theory, theory and practice are the same. In Practice, they're not. Every boat is different.

2. Someone already pointed out that wood in salt water can provide a current path, which deteriorates the wood. If you monitor it frequently, you can spot this before it's too late. the wood near metal fittings, throughulls, etc. will get white fuzzy. This is based on owning several wooden sail boats.

3. Excess sacrificial anodes can drive excess currents...not a good thing. I protect every piece of underwater metal with either an attached or a bonded sacrificial anode, but keep monitoring for signs of excess current leakage, now on a glass hull.

4. I agree that underwater plates are about grounding electronics and/or lightning strikes, not electrolysis, but they are subject to electrolysis like any other piece of metal.

Good luck.

Click to expand...

Respectfully disagree with #1, corrosion is all about electricity and physics, there is no witchcraft or black art involved. Those who don't fully understand the mechanisms by which it occurs often claim this is the case because they are unable to explain why it is occurring. If they can't 'follow the electrons' (and if they don't know electrons flow in metal, ions in water, that's a big red flag), then they aren't sufficiently schooled in corrosion analysis, and they should not be making pronouncements regarding your vessel's corrosion issues.

With rare exceptions, you should not entrust corrosion analysis to anyone who has not at least passed the ABYC Corrosion Certification, with a grade of 90 or higher.

Also, in the industry we eschew the word "electrolysis" as it is more accurately applied to hair removal. Here's what ABYC has to say on ths subject, "Electrolysis - the breakdown of an electrolyte resulting from current flowing in an electrochemical cell that includes that electrolyte, e.g., the breakdown of water into hydrogen and oxygen gases in a supplied-current electrochemical cell.
NOTE: The term “electrolysis” is often used loosely to describe corrosion in general, or the operation of supplied-current cells in particular. Its use in this respect is often confusing and is discouraged."

Most corrosion is either simple, galvanic or stray current, with sub-varieties. https://stevedmarineconsulting.com/unraveling-the-corrosion-mystery/

Reference cell testing is extremely valuable to identify issue, with little or no guess work https://stevedmarineconsulting.com/...rosion-protection-level-editorial-old-vs-new/