To Bond or not to Bond

In the middle of October I bought a 1985 43' Marine Trader Sundeck. During the survey we noticed it had bonding wires from each thru hull valve and to various other components (swim steps rudder bolts). It however didn't have a main zinc off the transom but instead simply had everything grounded to the bots motors. Several of the bonding wires were broken or detached but everything looked good as far as component corrosion only the rear rudder bolts appeared to be corroding.

Upon further inspection the rudder bolts were bonded to the bronze interior rudder struts thus they were corroding.

I have had two Marine Electricians look at it. One said either disconnect everything or attach everything again but no main transom zinc is needed.

The other said either re attach everything again and install a transom zinc with buss bar and run everything to it rather than the engines or disconnect everything and for sure don't have bonding from a bronze strut to a stainless rudder bolt or bolts. This guy put something in the water and did a reading on each engine which showed it was within the criteria for current/corrosion.

I am cutting the connection from the stainless bolts to the bronze immediately but wanted your advice on bonding or not bonding the thru hulls valves.
Leaving them as is or installing a central zinc on the transom.

I am leaning towards cutting everything to the valves and stainless bolts and going the non bonding route since the boat is in good shape and not corroded other than those few strut bolts which have minimal corrosion.

There is no "right" answer.....


You can follow ACYC suggestions or those by well suggested authors...but there is no consensus throughout my readings that all conform to the same advice.


I would read up as much as I could then make the decision.


The only thing that seems universal is the way to check to see if each piece of metal is protected well enough on its own or with zinc but not necessarily the "only" way to do it.

I second psneeld's thoughts above as well as your second electrician's. In fact the second electrician did a corrosion survey and measured the voltage between a reference electrode and your boat's underwater metals.
As psneeld notes there is no consensus among the experts. Most new boat builders do bond everything and use a transom zinc but other experts say that no bonding works just as good.


Since you already have the elements of a full bonding system in place, I would vote to restore that system with a the addition of a transom zinc.


I once read a comprehensive bonding/grounding/SSB ground plate/lightning protection article many years ago on one of these forums (can anyone retrieve it?) and as best I recall it said the same thing that your second electrician said.


David

Steve D'Antonio has written some excellent articles about bonding
Here is a link to one
https://stevedmarineconsulting.com/bonding-systems-and-corrosion-prevention/
Eric

http://www.kastenmarine.com/_pdf/mbqCref.pdf

A good article on the subject.

I agree with everyone that there is no right way technically. However, if you have everything bonded and you develop an electrolysis issue the zink would be a good indicator of a problem.

On my boat I have stainless bolts attaching bronze struts to the boat. You bet everything is bonded to a transom zink.

My current boat was built in 1942, has all thru hulls bonded, and all the original thru hulls are in excellent condition. If a thru hull should loose a zinc, it's still protected thru the bonding.

I've been bonding metal items or operated boats already bonded for about 60 years w/o problems. Why change something that works?

I'll 5th or ???? there is no entirely right answer.
Two books I have are :
Nigel Warren, Metal Corrosion in Boats
Everett Collier, The Boatowners Guide to Corrosion

I also agree that the second electrician is maybe the better of the two.

I will comment though that for no bonding then zincs must be used to protect many metals not only from the seawater but from interactions between metals in contact with each other.

Manganese Br Prop {not a true bronze| and SS shaft. Must be zinced.
Most through hulls since these days one cannot guarantee that all the directly attached metals are the same alloy.

Tiltrider makes a good point with his boat. SS bolts holding a bronze strut. Must be zinced and if not practical then bonded to a transom zinc.

I disagree with your comment QUOTE I am cutting the connection from the stainless bolts to the bronze immediately but wanted your advice on bonding or not bonding the thru hulls valves. END QUOTE
If those two metals. the brz and the SS bolts are in the seawater one of them will pay a price so be carefull. THey may have shown a good voltage BECAUSE they are zinc protected through the bonding. Remove that and the protection will disappear.
The through hulls and the valves should be protected by zincs , if need be by bonding, if the alloys are different.



READ THOSE BOOKS.
Another might be Nigel Calders, Boat Owners Mechanical and Electrical Manual as if I remember correctly it does tough on this subject, just not as extensively.

Untill you understand what you have simply clean up what you have, ensure good connections and go from there.

I felt like there was some urgency with the stainless rudder strut bolts starting to corrode since they were directly connected to the bronze struts (no zinc) they would corrode faster since the are less noble. I had an aluminum boat years ago with electrolysis issues so I read a lot about it but it's been too long. I have one of Nigels books on the boat I'll review.

No transom zinc appears to ever have been installed even the swim step which is fairly new has some wires running from the stainless bolts to the engine. It's as if every owner just followed what the previous owner had done without putting a main zinc on the transom, bonding everything to the engines.

All thru hulls look good, most have broken or lose bonding wires and many are very hard to get to to re bond so I thought disconnecting everything would be the best solution but I'll reconsider.

"On my boat I have stainless bolts attaching bronze struts to the boat."

Easily corrected at the next haul out.,,,Hamilton Marine has Silicone bronze strut bolts in most sizes.

FF said:

"On my boat I have stainless bolts attaching bronze struts to the boat."

Easily corrected at the next haul out.,,,Hamilton Marine has Silicone bronze strut bolts in most sizes.

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agree totally. And, don't forget the little guys on the shaft log(s). I had my SS nuts crack here, and they were on the dry (bilge side). It all went to SB.

On my boat except for my prop shaft 100% of the underwater metal is bronze. I put a zinc on the shaft but have not bonded anything else. I do have a question for the bonding advocates.



How do I bond the approximately 5,000 bronze screws that hold my hull planking on?

TDunn said:

On my boat except for my prop shaft 100% of the underwater metal is bronze. I put a zinc on the shaft but have not bonded anything else. I do have a question for the bonding advocates.



How do I bond the approximately 5,000 bronze screws that hold my hull planking on?

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Great question, but isn’t wet wood already somewhat conductive? Are these screws going away?

With many docks converting to the 30ma trip protection you may want to consider a thorough review of vessel's overall grounding and bonding (or not) system.

All the above is why it’s so hard to answer these type questions. I could generalize and say something like don’t bond wood boats and then some one would bring up an exception that needed bonding. Then you have the boat that started off life being non bonded and some one added to it changing the requirements but failing to bond. Even bottom paint choice can be affected by bonding.

My boat is fully bonded. That is what is best for my situation. That does not mean it’s what the next boat should do.

Derik said:

I felt like there was some urgency with the stainless rudder strut bolts starting to corrode since they were directly connected to the bronze struts (no zinc) they would corrode faster since the are less noble. I had an aluminum boat years ago with electrolysis issues so I read a lot about it but it's been too long. I have one of Nigels books on the boat I'll review.

No transom zinc appears to ever have been installed even the swim step which is fairly new has some wires running from the stainless bolts to the engine. It's as if every owner just followed what the previous owner had done without putting a main zinc on the transom, bonding everything to the engines.

All thru hulls look good, most have broken or lose bonding wires and many are very hard to get to to re bond so I thought disconnecting everything would be the best solution but I'll reconsider.

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If the bronze strut is held to the hull by those SS bolts then keep the bonding BUT figure out how to get that attached to a zinc which will protect both.
Without a bonding wire they are already bonded together by direct physical contact so removing the bonding wire will not help. Just a bonding wire between the two will do nothing unless a zinc is attached and that zinc is in the seawater.

Yeah, it sounds like none of the previous owners understood anything about the bonding and zincing. No expert here either.

Bond. James, Bond.

helm said:

Steve D'Antonio has written some excellent articles about bonding
Here is a link to one
https://stevedmarineconsulting.com/bonding-systems-and-corrosion-prevention/
Eric

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Thanks Helm. That's the Reader's Digest version. If you want a more thorough understanding of bonding (or if you have insomnia), here's the long version. https://stevedmarineconsulting.com/wp-content/uploads/2014/03/BondingSystems138_05.pdf

There are two approaches to underwater metal corrosion mitigation, bond and protect (with a sacrificial anode) or isolate. If you you take the latter approach, you are more vulnerable to stray current corrosion should that occur.

As far as screws in a timber hull, they are isolated. I have seen cases of failures in hull fastenings from stray current corrosion, but it's rare because stray current corrosion is in itself pretty rare, and timber hulls are pretty rare as well.

As far as a stainless bolt and a bronze strut are concerned, ideally all underwater fasteners should be silicon bronze, stainless is prone to crevice corrosion (which has no relationship to its contact with the bronze). Having said that, 90% of the struts I encounter are fastened with ordinary 18-8, the most corrosion prone type of stainless steel used for fasteners. The photo of the wasp-waisted cap screw in this article https://stevedmarineconsulting.com/stainless-steel-miracle-metal/ is from a 20 year old strut installation. This is crevice corrosion, it has little of anything to do with bonding, it's the result of stainless steel which is wet and robbed of oxygen.

If you must use stainless for underwater fastenings, it should be AISI 316. Did I say silicon bronze is preferred for underwater fastenings?

While I am not going to make a suggestion to the OP, I will say that owning a wooden, bronze-fastened hull for 29 years on the Pacific and Guf Coast made me a believer in the Electro-Guard system with is single small reference zinc on one side of the boat and its sacrificial zinc on the other side. Bonding must be a religion with such a vessel, especially the multiple shaft wipers. Bronze rudders with ss rudder posts through bronze glands. SS shafts and br props going through four br cultlass bearings and br shaft logs with ss fasteners. NO shaft/prop zincs; NO rudder zincs; just the two EG zincs. Never a problem. Pulling fasteners for the sale in 2015 showed a little bit of thinning at the interface, but nothing I would call serious.

I am a fan of electro-guard. While they are not necessary on a fiberglass boat they can alert you to stray current issues.

As has been said, bonding causes divisions amonmgst owners.

On our Fleming, everything is bonded, and bonded well. 2 main ship's anodes connect to everything. Shafts have zincs as do the stabilisers, bow and stern thrusters, engines, generators and the sea-water stabilser oil coolers.

The key for us is every year to ensure that all connections are well made and that nowhere is the impedence greater than 0.3 ohms between the main zincs and the item being bonded.

In 16 years, no problems. Yo my knowledge, all Flemings are done this way

I never worried about it till I got my steel hulled BR 44. Then I read everything I could find. No one agreed. It turned out the steel boat almost sank when a guy in the next slip dropped an AC line in the water and left it there for a week. His boat DID sink in the slip. Mine was protected by the issolation transformer, but the bronze back plate on the heat exchanger turned to dust and would have sunk the boat except that I was onboard when it failed. I now, no longer use shore power....ever..... On my MS 34 Mk1, from what I can see, nothing is bonded.. BUT, the diver says my zincs are in great condition so I wont be touching anything for now.

greatpapabear said:

As has been said, bonding causes divisions amonmgst owners.

On our Fleming, everything is bonded, and bonded well. 2 main ship's anodes connect to everything. Shafts have zincs as do the stabilisers, bow and stern thrusters, engines, generators and the sea-water stabilser oil coolers.

The key for us is every year to ensure that all connections are well made and that nowhere is the impedence greater than 0.3 ohms between the main zincs and the item being bonded.

In 16 years, no problems. Yo my knowledge, all Flemings are done this way

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Fleming does do a good job of bonding, and the standard you are holding them to is very lofty indeed, the acceptable resistance between anode and protected metal is 1 ohm. Your regular inspections are applauded, too few owners pay attention to bonding system maintenance.

One change Fleming has made at my request in the past few years is the means by which bonding wire ring terminals are connected to the copper bonding bus, they used to use tapping screws (these are prohibited by ABYC guidelines for electrical connections, bonding and otherwise), in the last couple of years they switched to machine screws.

Many, the majority of, boat builders use tapping screws for bonding connections, it nearly always results in high resistance because the connection loosens over time. These connections should be checked regularly, and where they can't be tightened, a bus bar, or at the very least a through bolt, installed in their place. The bonding article I shared earlier covers this subject.

Steve DAntonio said:

Fleming does do a good job of bonding, and the standard you are holding them to is very lofty indeed, the acceptable resistance between anode and protected metal is 1 ohm. Your regular inspections are applauded, too few owners pay attention to bonding system maintenance.

One change Fleming has made at my request in the past few years is the means by which bonding wire ring terminals are connected to the copper bonding bus, they used to use tapping screws (these are prohibited by ABYC guidelines for electrical connections, bonding and otherwise), in the last couple of years they switched to machine screws.

Many, the majority of, boat builders use tapping screws for bonding connections, it nearly always results in high resistance because the connection loosens over time. These connections should be checked regularly, and where they can't be tightened, a bus bar, or at the very least a through bolt, installed in their place. The bonding article I shared earlier covers this subject.

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Hi Steve, thank you. You are so right about the self tapping screws. I've changed so many after finding they'd become loose or corroded, I've lost count. I've also found some 'flexible' earthing wires to be only a few cores and therefore inflexible when used on moving parts such as the rudder bar.

However, it's all in a day's maintenance. Mind you, I say that, but a full engine (2 x main & 2 x generator) and general service takes me a good 8 days. leaving many aches and pains which take the rest of the year to get over!

jimisbell said:

I never worried about it till I got my steel hulled BR 44. Then I read everything I could find. No one agreed. It turned out the steel boat almost sank when a guy in the next slip dropped an AC line in the water and left it there for a week. His boat DID sink in the slip. Mine was protected by the issolation transformer, but the bronze back plate on the heat exchanger turned to dust and would have sunk the boat except that I was onboard when it failed. I now, no longer use shore power....ever..... On my MS 34 Mk1, from what I can see, nothing is bonded.. BUT, the diver says my zincs are in great condition so I wont be touching anything for now.

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I'm an advocate of isolation transformers (especially on metal boats but all hulls benefit), they are invaluable for a variety of reasons, detailed here http://stevedmarineconsulting.com/wp-content/uploads/2014/03/Transformers.pdf

While I don't doubt what you experienced, it's worth pointing out that the incidence of AC (shore power) induced corrosion is extremely low, and when it does occur it usually is harmful primarily to aluminum (hulls, and stern drives typically). Stray AC leakage is very common in marinas, it's why you shouldn't swim there, but it's not a corrosion risk per se.

Also, stray AC (or DC for that matter) current outside your boat, especially a steel hull, almost never causes corrosion on an internal component like a heat exchanger, because they are considered to be in 'different bodies of water', the current will not travel past the steel hull, up a long, narrow hose and to the heat exchanger. Also, if you had properly wired isolation transformer, the circuit between the boat with the leaky shore power and your heat exchanger could not be completed in any event. This is also why the pencil anodes in a heat changer don't protect your prop and shaft, and why running gear and hull anodes don't protect heat exchangers, they are in different bodies of water.

Again, I don't doubt you experienced these failures, but I do question the claimed means by which they occurred.

This article details the two most common types of corrosion, explaining how they occur https://stevedmarineconsulting.com/unraveling-the-corrosion-mystery/

This one covers aluminum specifically https://stevedmarineconsulting.com/understanding-and-preventing-aluminum-corrosion/

Steve DAntonio said:

I'm an advocate of isolation transformers (especially on metal boats but all ,,,,

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Me too. Plus, any xfmr i buy will have a 208v primary tap.

BTW, if your zincs last too long, something is probably wrong, they should erode. If they aren't eroding (they are actually corroding), or if they are getting marine growth on them, they probably are not connected to the bonding system, or underwater hardware, properly, with a low resistance connection. Again, one ohm is the maximum allowable resistance between anode and protected metal.

Does a grounding plate perform the same function as a transom zinc?

albinalaska said:

Does a grounding plate perform the same function as a transom zinc?

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No. It is not sacrificial.