Bonding System to avoid galvanic corrosion

[AleCiotti]

Hi guys i'm new here and also new to the boat world, i have a sailboat that has a bonding system to avoid galvanic corrosion and i also think to help with lighting?

But the system seems to be interrupted or not working properly as you can see from the photos below, I'm studying the subject and from what I've read the electrical components should be connected singularly one by one and the general metal components that are in contact with electrolytes (such as salt water) can be all connected together all the way to a sacrificial anode, i think we are using zinc in my boat (as for the keel), but i don't know where is the anode for the general metal components..

Anyway that's me rumbling about the very little that i know, if you have any tips on how to proceed or any information to look at to help solve the issue i would gladly appreciate it!

[Cheechako]

Bonding is a controversy. I suppose it's all about every detail of a particular situation.
I've seen bonded boats with bad corrosion issues. I've had bonded boats with no problem and unbonded boats with no problem.
In my head I tend to think: "anything tied to another thing is just asking for stray current or etc"

[HeinSdL]

Would be keen to understand this topic better mainly because I can only visualize downside to bonding. Stray currents in a marina will prefer the bonded thruhulls, prop, etc so there you go, corrosion. Engine on my boat is fully isolated when not in use, purely to ensure the saildrive doesn't become some kind of cathode/anode immersed in salt water.

So I would be in the camp, don't! But happy to hear arguments for.

[Statistical]

There are two schools of thought when it comes to bonding.

The first is connect every single underwater metal surface together via bonding wire and then also connect that "bonding system" to a sacrificial anode. When done right it does work. The anode rather than protecting a single directly attached component is providing protection to all indirectly wired components. The challenge is that sometimes the bonding wires themselves becomes loose or get corroded. If you don't have a zero low resistant reliable connection between every single underwater metal component and the sacrificial anode it is worthless arguably worse than worthless it could even accelerate corrosion.

The second school of thought regarding bonding is ... don't. This is only possible on fiberglass boats. However if you have a plastic boat and have thruhulls connected by hose there is not a solid connection between any underwater elements. They have a high degree of isolation and attempting a bonding system may just make things worse. Use noble materials where possible for example thruhulls. Provide anode of specific components only which are not noble (propshaft & prop).

The first school of thought is more common in Europe and the second one more common in the US. There are significant exceptions on both sides of the argument though. The one thing which is absolutely true is an incomplete bonding system that is multiple dissimilar metal components connected together and NOT connected to an anode is the worst of both worlds. You have a purpose built system to vastly accelerate corrosion. In essence you are turning your metal components into components of a accidentally built battery.

So how to fix it. You need to do one or the other. It is all or nothing. Either rip out the entire bonding system and attach sacrificial anodes to non-noble components directly OR rebuild the bonding system. If you rebuild it and can't find the intended anode location install a new one. Everything must the bonded to each other and the anode. You may need to replace wire and/or cleanup connection points.

The one thing you can do is leave it in a halfway state that is hyper accelerating any corrosion.

Personally if it were my boat I would just rip out the bonding system, replace any improper materials (i.e. brass thruhulls/valves), put anodes on specific things which need it (i.e. prop shaft). Bonding is IMHO one of those things which looks good on paper but often fails in the real world. It isn't hard to get right but it is easy to get wrong and something a simple a single wire knocked loose and forgotten can render the entire system worthless actually worse than worthless actively harmful.

[Cheechako]

Originally Posted by HeinSdL

Would be keen to understand this topic better mainly because I can only visualize downside to bonding. Stray currents in a marina will prefer the bonded thruhulls, prop, etc so there you go, corrosion. Engine on my boat is fully isolated when not in use, purely to ensure the saildrive doesn't become some kind of cathode/anode immersed in salt water.

So I would be in the camp, don't! But happy to hear arguments for.

That's the dilemma isn't it?
I went to a presentation once years ago. A Valiant 32 had sailed the world and it was fine for years. It came home to Seattle and had a new cutlass bearing, shaft and packing done.
It sat in the marina for several months and a bottom cleaning diver told the owner "you need to haul this boat immediately".
The through hulls and shaft were almost completely corroded apart! The sample of shaft I saw looked like a lace tablecloth!

[AleCiotti]

Originally Posted by Statistical

There are two schools of thought when it comes to bonding.

The first is connect every single underwater metal surface together via bonding wire and then also connect that "bonding system" to a sacrificial anode. When done right it does work. The anode rather than protecting a single directly attached component is providing protection to all indirectly wired components. The challenge is that sometimes the bonding wires themselves becomes loose or get corroded. If you don't have a zero low resistant reliable connection between every single underwater metal component and the sacrificial anode it is worthless arguably worse than worthless it could even accelerate corrosion.

The second school of thought regarding bonding is ... don't. This is only possible on fiberglass boats. However if you have a plastic boat and have thruhulls connected by hose there is not a solid connection between any underwater elements. They have a high degree of isolation and attempting a bonding system may just make things worse. Use noble materials where possible for example thruhulls. Provide anode of specific components only which are not noble (propshaft & prop).

The first school of thought is more common in Europe and the second one more common in the US. There are significant exceptions on both sides of the argument though. The one thing which is absolutely true is an incomplete bonding system that is multiple dissimilar metal components connected together and NOT connected to an anode is the worst of both worlds. You have a purpose built system to vastly accelerate corrosion. In essence you are turning your metal components into components of a accidentally built battery.

So how to fix it. You need to do one or the other. It is all or nothing. Either rip out the entire bonding system and attach sacrificial anodes to non-noble components directly OR rebuild the bonding system. If you rebuild it and can't find the intended anode location install a new one. Everything must the bonded to each other and the anode. You may need to replace wire and/or cleanup connection points.

The one thing you can do is leave it in a halfway state that is hyper accelerating any corrosion.

Personally if it were my boat I would just rip out the bonding system, replace any improper materials (i.e. brass thruhulls/valves), put anodes on specific things which need it (i.e. prop shaft). Bonding is IMHO one of those things which looks good on paper but often fails in the real world. It isn't hard to get right but it is easy to get wrong and something a simple a single wire knocked loose and forgotten can render the entire system worthless actually worse than worthless actively harmful.

Got it, thanks a lot for the detailed answer, I'm thinking of trying to follow the bonding cable around until I "hopefully" find the sacrificial anode, and then redoing all the bonding with new cables.. on this matter which cables should I use? is there a guide you know of to do this?
Thanks!

[Bowdrie]

Bonding, per se, isn't anything new, nor is it always bad or always good,
I spent an extensive period of time renovating a 55' Chris-Craft motoryacht built in 1959.
It had a factory installed bonding system consisting of a fairly heavy gage copper strip which ran thru the length of the bilge and everything that was metallic had feeder wires running down to that strip, that strip being connected to an external ground plate, (not a zinc).
Of course, when it was built the AC on board consisted of a battery charger, a water heater, and a few scattered outlets.
Things like screwing brass fittings into galvanized fuel tanks, (or giant gate valves for engine intakes,) weren't the greatest, but it had lasted for, (at the time,) ~55 years.
But that was in fresh water, a poor electrolyte compared to salt water.
We've learned that isolated bronze seacocks/thru hulls do NOT need any bonding to prevent their "going away", left alone they do just fine, and any zinc connected to them results in "overprotection".
It used to be common for good quality boats to have ALL underwater metals in bronze; seacocks/thru hulls, fastenings, shafts, props, rudder shafts, struts, swim step supports, even the housings for the depth sounder transducer and speed log.
And the fuel tanks were of Monel, the water tanks of copper.
And a sailboat would have a lead keel with bronze bolts.
Things changed when various metals were thrown together.
Iron keels, stainless bolts, aluminum outdrives, stainless bobstay fittings and stainless rudder shafts/prop shafts, and inferior bronze alloys, (DZR,) became common.
Now things started "going away" underwater, the answer became lots of bonding and lots of zinc.
If bonding has shown us anything, it is that any and all steps necessary to prevent any electrons from the positive side of a DC circuit entering that bonding system MUST be done.
There is also the related issues of AC protection and lightning protection, but those are other stories not germane to the thread title.
Ya know, on second thought, most of what I've typed has little to do with "Galvanic corrosion", being more geared towards "Stray current corrosion".
Oh well.

[boatpoker]

As a retired Certified Marine Corrosion tech I won't even attempt to get into this discussion, It is far too complex to explain in a few paragraphs but I will send you off in the right direction ...

1. Install a galvanic isolator (Failsafe type) on your boat.

2. Learn the difference between Galvanic Corrosion and Stray Current Corrosion.

3. Learn the difference between bonding, lightning protection, grounded and grounding conductor.

3. Buy a silver/silver chloride half cell and learn how to use it. This one comes with a well written instruction booklet but there are others.
https://boatzincs.com/cre/

4. I haven't seen anyone use it in this thread yet but someone somewhere will talk about "electrolysis". Never take marine electrical advice from anyone using that term.

[AleCiotti]

Originally Posted by boatpoker

As a retired Certified Marine Corrosion tech I won't even attempt to get into this discussion, It is far too complex to explain in a few paragraphs but I will send you off in the right direction ...

1. Install a galvanic isolator (Failsafe type) on your boat.

2. Learn the difference between Galvanic Corrosion and Stray Current Corrosion.

3. Learn the difference between bonding, lightning protection, grounded and grounding conductor.

3. Buy a silver/silver chloride half cell and learn how to use it. This one comes with a well written instruction booklet but there are others.
https://boatzincs.com/cre/

4. I haven't seen anyone use it in this thread yet but someone somewhere will talk about "electrolysis". Never take marine electrical advice from anyone using that term.

That's Awesome, thanks for all the resources, I will start studying them!