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Old 10-16-2020, 06:51 AM   #1
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Thru-hull bonding

Just hauled for the winter after 6 mos in the water. All my thru hulls are covered in barnacles and zincs are greatly depleted. Suspect some sort of bonding/electrical issue. Interestingly, I found this article that says NOT to bond thru-hulls. All the thru hulls on my Mainship Pilot are electrically bonded. Seems like there are arguments to be made for both methods. I'm thinking maybe I should un-bond for a season and see what happens. This boat is new to me so I don't have a lot of history, not like this was always fine until this year. Thoughts?

https://www.westmarine.com/WestAdvis...unding-Systems
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Old 10-16-2020, 07:58 AM   #2
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Depending on how much metal you have in the water vs how much zinc, it’s not unusual at all for zincs to have a lot of depletion after 6 months. I’d say mine are about 40% depleted after that amount of time. It’s also possible if you’re plugged in at a marina that nearby boats are exacerbating your zinc usage. IMO all underwater metals should be bonded. Anything that’s not bonded is not protected from galvanic action, at risk if there’s ever stray current and also all metals being bonded Is thought to reduce damage in the event of a lightning strike.
If there’s no anti fouling on your through hulls then you’ll get barnacles. I haven’t heard of any barnacle issues related to galvanic currents.

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Old 10-16-2020, 08:25 AM   #3
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Depending on how much metal you have in the water vs how much zinc, itís not unusual at all for zincs to have a lot of depletion after 6 months. Iíd say mine are about 40% depleted after that amount of time. Itís also possible if youíre plugged in at a marina that nearby boats are exacerbating your zinc usage. IMO all underwater metals should be bonded. Anything thatís not bonded is not protected from galvanic action, at risk if thereís ever stray current and also all metals being bonded Is thought to reduce damage in the event of a lightning strike.
If thereís no anti fouling on your through hulls then youíll get barnacles. I havenít heard of any barnacle issues related to galvanic currents.

Ken
Not sure if you read the link I posted. I'm no expert, but galvanic currents can cause paint to blister on metal, causing them to become fouled. More details on my situation, everything was painted and new zincs at start of the season. I would say my rudder zinc and the transom plate are the worst. Rudder zinc about 80-90% gone. I agree about stray currents at the marina and that's why the article says not to bond thru-hulls. It allows current paths thru your bonding system that wouldn't exist if they are unbonded. For instance, current could be traveling into a thru-hull and out my rudder zinc.
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Old 10-16-2020, 10:43 AM   #4
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My advice, get your bonding system checked by a professional.
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Old 10-16-2020, 11:56 AM   #5
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My advice, get your bonding system checked by a professional.
Thanks, I am doing that but I think you are missing the point. At least if you believe the West Marine article. My bonding system could be 100% intact but if there are stray currents in the water from nearby boats, the bonded thru hulls makes the problem worse instead of better. The path of least resistance would be through my boat instead of the water.
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Old 10-16-2020, 12:08 PM   #6
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Thanks, I am doing that but I think you are missing the point. At least if you believe the West Marine article. My bonding system could be 100% intact but if there are stray currents in the water from nearby boats, the bonded thru hulls makes the problem worse instead of better. The path of least resistance would be through my boat instead of the water.
As I understand it, your bonding system is tied into your large zinc plate and this should protect your boat, including your bronze hull valves.
All your zincs will deteriorate faster than expected.
This is why I encourage you to discuss it with a qualified electrician.
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Old 10-16-2020, 12:32 PM   #7
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I am having a professional look at it. You are still missing the point though and maybe you don't understand what I am getting at. There are 2 schools of thought. One says thru-hulls should be bonded, another says it's better if they are not. That was covered in the article I posted from West Marine recommending against bonding and that was why I started this post to get some feedback and opinions from others.
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Old 10-16-2020, 01:11 PM   #8
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There are many schools of thought... Totally un-bonded (rare) all the way to bond everything.

You didn't say if you were in fresh water or salt, or amount of time spent at the dock.
If you spend a while at the dock, with shore power connected, either you or someone nearby could have an electrical leakage causing wasting of your zincs and putting all nearby boats at risk.

As others have said "Get a pro" or a VOM and a silver half cell probe and find out how much electrical potential your boat has. Walk around the boat and see if it varies. Chances are, it's going to be worse near your stern, since you've reported zinc depletion there.

Disconnect the shore power and do the same walk around the boat checking values. If the potential is different, your boat has electrical current leakage. If not, probably other boats nearby have a problem. Get a long ground wire and test along the dock for the highest potential from the water to the dock pedestial and chances are, you've foud the culprit.

But, this is electricity we're talking about, and unless you've got some history or training, get a pro who does. Some boats have after-market inverters that have a house bond tying neutral to ground and that can cause leakage.

Also, if you have accelerated zinc wasting, check the edges of your prop[s] since the sharp edges will be wasting next, or already. That's a common sign of leakage, when you see a boat with a chewed up feather edge of the prop.
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Old 10-16-2020, 01:28 PM   #9
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There are 2 schools of thought on this subject. I know quite a bit about electrical work on boats but am certainly not an expert on this subject. So I listen to experts like Steve D. He recommends bonding I believe. In the US bonding is the norm, in Europe I think that not bonding is the norm. As said by others get a certified marine electrician to check your boat. Whether to bond or not is up to you. Personally I bond. Last winter I refurbished the port side of my bonding when I had the port engine out. This winter I will refurbish the starboard side of the bonding system after we pull the starboard engine.
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Old 10-16-2020, 01:43 PM   #10
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Galvanic isolator?
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Old 10-16-2020, 03:06 PM   #11
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The PO did a 15 year resto on my 1979 49ft MT RPH. All bonding was removed. Zincs on shafts, rudders and struts lasted about a year. No big deal. Everything else looked good. I went ahead and replaced them all with Aluminum anodes, added a Divers Dream plate and bonded these parts together. I did not bond them to my engine/trans, batteries, electrical system or other thru-hulls. (there is a 50 ohm difference between my transmission and shaft, taking the trans/engine out of the equation).



I am in brackish water on the Potomac. My Silver-Silver Chloride testing anode shows I have about -0.9VDC of protection. Dead center where I want it. Similar readings with all other thru-hulls show 0.0. A bronze or stainless thru hull sitting by itself with a rubber hose connected does not add to the equation in the slightest. If anything, bonding that and adding it into your system could (I said "could") promote more stray current to enter your ground plane.



On the other end, I do have dual galvanic isolators for the electrical coming from the dock, just in case a ground is ever made somewhere by mistake.



I am going to try this route for two years and then re-evaluate if need-be after that. So far so good though. I do wonder about barnacle build-up on my driver dream though.
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Old 10-16-2020, 03:37 PM   #12
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I appreciate everyone's feedback. Some further info. Boat is docked near the mouth of a river, so water is either salt or brackish depending on the tide. The boat is a 2012 and has a transformer. I did a test with a silver chloride anode and the voltage was fine, pretty much right in the the middle of the range and changed very little when plugged into shore or anything else I tried. I think that means that my bonding system is intact and protecting my boat. However, I don't think that tells me much if anything about stray currents. My understanding is that bronze thru-hulls should not suffer from galvanic corrosion, but when they are added to the bonding system can add a path through my boat for stray currents. I'll let the experts figure it out, but I was wondering if anyone else has had similar issues or experience with something like this.
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Old 10-16-2020, 03:44 PM   #13
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Test the voltage at different times of day, days of the week, and with different things on the boat turned on...

Also, are you using zinc, zinc alloy, or aluminum anodes?

Bronze can suffer from dezincification where the current releases the zinc ions from the surface accessible bronze, but that's if you have a stray current problem.

If you've tested everything and your immediate vicinity, over different days and times, and still have no leakage problems, then your know your anode replacement schedule is every 6 months or so.

If your dock neighbor has an electric grill and uses a few times a week, and they have a problem, you have a problem too. Doing the stray current test once is not a once and done thing. I think boats should have a display showing the current differential, simply to warn against ESD, since fresh water is far more deadly with ESD than salt water boats...
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Old 10-16-2020, 03:54 PM   #14
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If your through hulls are covered in barnacles, they're not subject to any stray currents, it would seem. I'd leave everything as it is if your underwater hardware looks ok.
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Old 10-16-2020, 04:21 PM   #15
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Quote:
Originally Posted by backinblue View Post
Not sure if you read the link I posted. I'm no expert, but galvanic currents can cause paint to blister on metal, causing them to become fouled. More details on my situation, everything was painted and new zincs at start of the season. I would say my rudder zinc and the transom plate are the worst. Rudder zinc about 80-90% gone. I agree about stray currents at the marina and that's why the article says not to bond thru-hulls. It allows current paths thru your bonding system that wouldn't exist if they are unbonded. For instance, current could be traveling into a thru-hull and out my rudder zinc.
The article in the link was a reprint of an article by one person, his opinion. Frankly, I’ll stick with the recommendations of acknowledged experts and the ABYC. Every piece of underwater metal in my boat is verified bonded and no issues.

https://stevedmarineconsulting.com/w...tems138_05.pdf

https://newboatbuilders.com/pages/electricity14.html

Ken
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Old 10-16-2020, 05:42 PM   #16
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When I bought my boat, it had the "plastic" through hull valves. No need for bonding. Well, those valves were almost 10 years old and I am 'old fashion'. I had them changed to bronze and bonded to the plate on the stern along with the normal stuff.
Every time I have the bottom painted, I have the through hull valves serviced too.
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Old 10-20-2020, 09:45 AM   #17
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My last boat had no bonding system. I had it professionally built and I argued this with the builder for a while. He was a very experienced guy who had access to some great minds. It was a cold-molded wooden boat and he stuck with the wooden boat view that you electrically isolate underwater metals and don't bond. I think the argument was bonding caused de-lingification of wood and was more likely to hurt the boat than galvanic corrosion of under water metals. It seemed to work and over the years I've payed close attention to discussions like this and am now convinced he was correct. The key is "you can avoid bonding IF you can electrically isolate metals".

I did have protection on my shaft for obvious reasons.

Regarding the de-zincification of bronze comment above: I thought bronze had so little zinc (depending on the alloy, possibly 0 zinc) that this wasn't an issue. If you had enough zinc for de-zincification to be a problem, then you wouldn't have bronze, it would technically be brass (which DOES suffer from de-zincification and that's why it's not used below the waterline).

Am I mistaken on that point?
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Old 10-20-2020, 01:47 PM   #18
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Not sure if you read the link I posted. I'm no expert, but galvanic currents can cause paint to blister on metal, causing them to become fouled. More details on my situation, everything was painted and new zincs at start of the season. I would say my rudder zinc and the transom plate are the worst. Rudder zinc about 80-90% gone. I agree about stray currents at the marina and that's why the article says not to bond thru-hulls. It allows current paths thru your bonding system that wouldn't exist if they are unbonded. For instance, current could be traveling into a thru-hull and out my rudder zinc.
If you have a Galvanic Isolator you cannot suffer from DC stray current from other boats.
AC current can cause corrosion but not enough that you're likely to notice it in your lifetime.
Sound to me like you anodes are doing what they are supposed to do.

As a Certified Marine Corrosion Analyst I could spend all day picking out misinformation and contradictions in that article and I'm surprised that WestMarine published it.

Check out this website on the issue. He is a retired nuc sub commander and consultant to BoatUS and USCG on ESD and corrosion. http://qualitymarineservices.net/
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Old 10-20-2020, 02:03 PM   #19
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Agree that A/C doesnít cause much if any corrosion. On a previous boat I was in the engine room and put my hand in the bilge water and got a shock while I was touching the engine. Measured the water and had something like 48 VAC. Started checking and found that the PO had changed the shore power inlet and swapped the ground and neutral. Also he used 14 gauge wire. The white neutral wire was scorched brown. I replaced the shore power inlet since when I looked closely it was starting to melt. I used 10 gauge wire and wired it properly. Checked the bilge water and the 48 VAC was gone. It had been like that for at least 2 years and we had no corrosion on any of the thru hull fittings. Now DC can do major damage in a few hours.
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Old 10-20-2020, 02:11 PM   #20
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Agree that A/C doesn’t cause much if any corrosion. On a previous boat I was in the engine room and put my hand in the bilge water and got a shock while I was touching the engine. Measured the water and had something like 48 VAC. Started checking and found that the PO had changed the shore power inlet and swapped the ground and neutral. Also he used 14 gauge wire. The white neutral wire was scorched brown. I replaced the shore power inlet since when I looked closely it was starting to melt. I used 10 gauge wire and wired it properly. Checked the bilge water and the 48 VAC was gone. It had been like that for at least 2 years and we had no corrosion on any of the thru hull fittings. Now DC can do major damage in a few hours.
The perfect scenario for an ESD fatality.
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