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Old 02-02-2022, 07:02 PM   #21
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A question for timber boat owners re: grounding plates

As explained to me it has to do with the properties of wood. The lignin in the wood fibers acts as a type of capacitance when interacting with saltwater. Excessive zincs cause a current flow through the wood and leeches the lignin out of the fibers and causes eventual failure. Fiberglass doesn’t have that issue.
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Old 02-02-2022, 11:56 PM   #22
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As explained to me it has to do with the properties of wood. The lignin in the wood fibers acts as a type of capacitance when interacting with saltwater. Excessive zincs cause a current flow through the wood and leeches the lignin out of the fibers and causes eventual failure. Fiberglass doesn’t have that issue.
I have read something similar to that too. But really am not sure since we have not owned a wooden boat since the 70s and then it was in fresh water.
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Old 02-03-2022, 12:39 AM   #23
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I have sold Tidahapah now but in the 26 years I had her the only earthing was between the outer stern tube bearing and an anode attached to the hull. About 14 years ago I had an electrical guy come on board and test for current and his recommendation was to get rid of half my existing anodes, I did this and the boat was good, the anodes worked well and I would get 2 years out of them. One was on the rudder (steel) the others were attached to the steel shoe on the keel.
All skin fittings were in good condition and never any electrolysis problems.
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Old 02-03-2022, 01:30 AM   #24
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I have sold Tidahapah now but in the 26 years I had her the only earthing was between the outer stern tube bearing and an anode attached to the hull. About 14 years ago I had an electrical guy come on board and test for current and his recommendation was to get rid of half my existing anodes, I did this and the boat was good, the anodes worked well and I would get 2 years out of them. One was on the rudder (steel) the others were attached to the steel shoe on the keel.
All skin fittings were in good condition and never any electrolysis problems.
Yep, think I'll keep winding back the anodes
1 on the old "Grounding Plate"
2 on the nozzle vs 6
And 3 on the shoe vs 12.

Less is more (-;
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Old 02-03-2022, 02:22 PM   #25
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Re the grounding plate. I always had that as it was connected to my HF radio that I still had in service. But that was the only thing that was ever connected to it.
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Old 02-03-2022, 03:00 PM   #26
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Old 02-03-2022, 11:34 PM   #27
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Re the grounding plate. I always had that as it was connected to my HF radio that I still had in service. But that was the only thing that was ever connected to it.
Was that a sintered bronze or just an anode grounding plate?

Wondering if the anode grounding plate on ours was a leftover from when she had HF as a work boat.
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Old 02-04-2022, 12:50 AM   #28
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Was that a sintered bronze or just an anode grounding plate?

Wondering if the anode grounding plate on ours was a leftover from when she had HF as a work boat.
Usually for the HF radios it was sintered bronze because they look huge, electrically, compared to any regular metal. There is some dispute about how well they work and the claims as to how big they look electrically. Who knows.
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Old 02-04-2022, 02:28 AM   #29
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Before SSB radios, we had AM sets. Not a radio tech but was told AM radios needed a ground to push against when transmitting. Back then most boats were wood and had a large copper plate on the bottom, usually about 3'x5'. It was also used as a lightening ground.

Like many fishing tuna, kept my AM radio because with a booster it had extreme range. At the right time of day, I could talk to people in the South Pacific, Gulf of Mexico and even Chile.
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Old 02-06-2022, 04:02 PM   #30
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Was that a sintered bronze or just an anode grounding plate?

Wondering if the anode grounding plate on ours was a leftover from when she had HF as a work boat.
It was a wave style sintered bronze earth/grounding plate. They were wave form to increase the surface area.
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Old 02-07-2022, 01:10 PM   #31
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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.
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Old 02-07-2022, 02:07 PM   #32
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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.
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Old 02-07-2022, 02:19 PM   #33
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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.
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/u...osion-mystery/

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