Thru-hulls, to bond or not to bond...

[rwthomas1]

I started this new thread to discuss thru-hull bonding instead of highjacking the Forespar Seacocks thread.

The way I understand it the bonding does create a battery but this is a good thing. The less noble metal in the bonding chain, the sacrificial zinc, is consumed instead of anything else. Simply having the thru-hulls unbonded is not the solution IMHO. The thru-hulls are still immersed in the electrolyte (seawater) and still subject to electrolysis because of that.

Additionally, the seacocks I have looked at, Groco, Algonquin, Apollo, etc. all have either stainless or chrome plated balls and bronze bodies. Is this not the definition of a battery, two dissimilar metals in an electrolyte? Bonding should protect the assembly from this?

I am not trying to be disagreeable/arguementative just want to see if this can be answered definitively. I am trying to find the Calder book..... FWIW, I have not yet bonded my Groco's but that is the plan for this year. RT

 

[treilley]

What happens when we throw lightning into the mix? Your mast gets hit, if your thru-hulls are bonded, do you not risk having them destroyed?

 

[Howard Keiper]

If you go to Google, Marine Grounding Systems, you will find a West Marine Advisor reprint of a paper by Stan Honey, originally published in The Practical Sailor, October 15th, 1996. There is more information in that particular paper re Grounding / Bonding than you're likely to find anywhere. And it's not a good idea to argue the point with Mr. Honey, either.

Bottom line...don't EVER bond your thru-hulls.

howard keiper
Sea Quest
Berkeley

 

[gareth harris]

West Marine Advisor reprint of a paper by Stan Honey

howard keiper
Sea Quest
Berkeley

'Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

It's worth understanding the reason. In an increasing number of marinas, there are substantial DC electric currents running through the water. If your bits of immersed metal are bonded, the electric current will take the lower resistance path offered by your boat in preference to the water near your boat, and the current will flow into one of your bits of metal, through your bonding wires, and then out another bit of metal. The anodic bit of metal or thru-hull that has the misfortune to be on the "out current" side of the current running through your bonding system will also become "out metal" and will disappear, sometimes rapidly.'

Thanks, Howard, I had not thought of that before but it makes perfect sense.

 

[rwthomas1]

I found the Calder book and he makes no specific recommendation on thru-hulls. Sometimes they are bonded, sometimes they can be unbonded. He does however recommend bonding in the traditional way, as I expected, for the rest of the large metal bits of the boat. So what to do? Do you go around snipping your bonding wires based on what Mr. Honey claims? Or do you stick with the traditional bonding system already installed and as recommended by Calder? Me, I'm sticking with Calder. My boats on a mooring, rarely at a dock and there are no nor has there ever been any indication that I should be worried where I have the boat currently. I will however be checking things out with the multimeter next season. RT

 

[gareth harris]

Me, I'm sticking with Calder. My boats on a mooring,

I, too, have read the same by Nigel Calder, and am surprised he made no mention of stray marina current, since it is in general far, far more destructive than galvanic action. But in your case, on a mooring, that would not be an issue.

On the question of lightning, I have never read anything that had a lot of hard evidence on the likelyhood of a strike getting into bonding wires, but there have been cases where people grounded the mast to a through hull, and the boat went down. My own opinion is that I would not have any wires connected to through hulls on a boat in Florida.

Gareth
Freyja E35 #241 1972

 

[Howard Keiper]

What Gareth says.
I also like a statement, again from Honey's paper, that sums up the thru hull issue for me:
"An isolated bronze thru-hull doesn't need protection because it is not in electrical contact with another immersed dissimilar metal. If electrically isolated, high quality marine bronze, is electrochemically stable in seawater; nothing good can come from connecting wires to it.".
howard keiper
Sea Quest
Berkeley

 

[rwthomas1]

What Gareth says.
I also like a statement, again from Honey's paper, that sums up the thru hull issue for me:
"An isolated bronze thru-hull doesn't need protection because it is not in electrical contact with another immersed dissimilar metal. If electrically isolated, high quality marine bronze, is electrochemically stable in seawater; nothing good can come from connecting wires to it.".
howard keiper
Sea Quest
Berkeley

This was my original question "Additionally, the seacocks I have looked at, Groco, Algonquin, Apollo, etc. all have either stainless or chrome plated balls and bronze bodies. Is this not the definition of a battery, two dissimilar metals in an electrolyte? Bonding should protect the assembly from this?" There are in fact TWO dissimilar metals in all seacocks. Check for yourself. RT

 

[Howard Keiper]

Somehow, I knew you'd pick up on that.
Regardless, I'm in a marina all year, plugged in, and with a professional opinion to tout. I've decided to err, if at all, on the side of overwhelming evidence against bonding my thru hulls...a judgement call, I guess.
howard

 

[Emerald]

Hi,

regarding the different metals in the seacock, I think only a call to Groco will answer the question. Is it possible that the seat for the ball and the bushing around the shaft may insulate the materials from each other? Here's where a call to Groco will get a real answer.

.

 

[rwthomas1]

Yes, calling Groco likely will provide the answer. Actually there may be another solution to the issue of dissimilar metals in seacocks. Would be possible to attach a small zinc to each seacock? I am not advocating this as a practical exercise, rather an academic one. If in fact the issue of stray DC voltage is such a problem for some and if one also wanted to provide maximum protection for the seacocks, would attaching a small zinc to each work? Not practical since no manufacturer designs for this. Curious.

Howard, I understand now why thru-hulls should not be bonded and the reasons certainly have merit. I am not planning to bond mine however I don't plan on de-bonding the rest of my boat either. We keep a pretty close eye on her, there have been no issues in the past, so I plan on just testing in the spring. If it is working, why mess with it? RT

 

[NateHanson]

When I've peered into a seacock, I think I've seen a nylon seat surrounding the stainless ball. I don't think there's any metal-on-metal contact. I believe there's a nylon bushing around the shaft too.

 

[Emerald]

[snip] If in fact the issue of stray DC voltage is such a problem for some and if one also wanted to provide maximum protection for the seacocks, would attaching a small zinc to each work? [snip] RT

Actually, I've read about doing just that - each seacock with its own zinc. It's been awhile, but I think it probably was being discussed regarding wooden boats, as electrolysis in the thru-hulls will take out the wood, a real disaster. Wood boats are also, perhaps, the one type where bonding comes back with an overwhelming yes, and again it's to protect the wood, not the bronze. Of course, someone will find exception to this now I've said it, but it's what my wood boat friends tell me.

Now, what would be really cool is if we could harness all this stray current to charge our batteries instead of using a solar panel while our seacocks and thru-hulls dissolve


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