Bonding,Zincs

[casual]

In refitting my new to me boat I,removed all the thru hul fittings and found some with wires attached some not.In the stern of the boat there are two what I,will call zincs thru bolted to the outside it seems as though wires were running to these two zinc's I,removed them also.Do,I,need to reinstall these as I,have no plans to run all those wires back to the thru hull fittings as most were laying loose anway,Do those zincs serve a purpoase other than bonding the Thru hull fittings.In retrospect all the thru hull fitings removed were good.
Thanks for your time Guy's

[Blue Stocking]

To bond, or not to bond, that is the question : Shakespeare.
I guess you know that the purpose of linking the thruhulls with cable is to equalise any electrical potential between the different alloys of bronze. The connection to the zincs is so that it may be sacrificed, instead of the bronze.
Wars have taken place over which is correct.
I bond , because I have a corrosion meter and have seen the evidence, therefore I believe.

[casual]

As I,guessed,In 30 plus years of sailboat ownership I,had never bonded frankly never paid much attetion to it,Never had a thru hull problem,I just removed all on this boat they were as new.Now I Got to Think,You make a valid point If I,dont bond I,have 6 holes to fill.What's a corrosion meeter and how do u install ?
Thanks for the relply

[Blue Stocking]

The corrosion meter is not a permanent installation, but a piece of test equipment for measuring the difference in potential between the bronze fittings and a known potential test cell.
The cell is immersed, and each disconnected thru hull is measured against it. It will show you where in the 1 1/2 volts of a simple cell that thruhull rates against the known standard.
Thats the abreviated explanation. It can get involved.

[GordMay]

See ➥ Using a Corrosion Test Meter

And ➥ Corrosion Testing

[casual]

GordMay,I,addhear to your philosiphy 100%So I,want to do it right the first time.At my dock I,have kept sailboats for 30 years .I,have never experienced other than normal zinc corrosion,any corrosion .I,will study the articles you provided.Being that as it may should I,bond?PS I,am not tech minded.
Thank you folks so much for the input.

[Saltyhog]

On my CR38, it's not just the thru-hulls that are bonded to, and therefore protected by, those 2 zinc plates. Also bonded are the shaft-log/tail-piece and the rudder shaft. When I replace the thru-hulls next winter, I plan to keep the bonding of all to those zinc plates. If the bonding is done correctly, it can only help and not hurt anything. The only time bonded thru-hulls can be a problem is in certain "hot" marina problems, and this should be dealt with in other ways (best way is an isolation transformer for shore power). Hope it helps.

[chris07732]

Are AG/AGCl electrodes available as a "consumer/handyman" tool. I can only find them as a laboratory item, certified accurate, etc. for +/- $200. We DIY boaters don't really need that kind of accuracy. Has anyone been able to purchase one? Is there a work around that anyone has used?

[delmarrey]

The problem arises when one has different metals in contact with each other under water. e.g. bronze prop/SS prop shaft. This is why shaft zinks are so important. As for thru hulls, if they are all bronze w/bronze fittings attached then they will only corrode in relation to time vs size. Plastic fittings will have no affect.

The bonding process protects the least of these, the smallest fitting, to last as long as the rest.
If you were a fisherman that spends lots of time at sea and had a lot of thruhulls, then bonding would definitely justify itself. Or if a boat spends it's time sitting in a HOT marina.
In the wooden boat days, it was important b/c a bad thruhull would damage the surrounding wood. I remember having to goto larger thruhulls to avoid replacing wood planks.

It's a choice for the life style of the boat.

Here's some reading material: http://newboatbuilders.com/docs/CorrosionOnBoats.pdf

[Vyndance]

When you say my dock, are you reffering to a private dock? If so this could be why you have never had any problems. If you are in a marina you have been lucky.

Put 2 dissimilar metals in an electrolyte solution and you have a battery. That is what is going on under your boat. The zinc is the anode(positive) and the bronze, your prop, thru hulls is the (cathode). Of your 2 dissimilar metals 1 is less noble than the one you want to protect.Electrons are going to flow from the positive to the negetive in your battery, from the anode to the cathode and take little bits of metal away from the anode in the process. This is why the zinc erodes over time protecting your prop. If the zincs dissapear the bronze now becomes the anode because it is less noble than stainless steel(the prop shaft, strut bolts) and the prop and thru hulls start to dissolve. The process is going to happen. You can't stop it. Bonding completes the circuit, allows all the bronze to become one so nothing is singled out in the circuit. The boat needs to be bonded from the grounded and grounding conductor to everything that contacts the water to the plate zinc.

[Vyndance]

Originally Posted by chris07732

Are AG/AGCl electrodes available as a "consumer/handyman" tool. I can only find them as a laboratory item, certified accurate, etc. for +/- $200. We DIY boaters don't really need that kind of accuracy. Has anyone been able to purchase one? Is there a work around that anyone has used?

Yep!

[casual]

Thanks al I,am learing,My boat is Kept at MY home.I,usually have shore power connected,for battery maintence.This New to me Cabo Is a Learing curve after 22 years with my last boat Its a Big Curve'
Saltyhog you mention that the 2 zincs thru bolted P&S aft connect to the Rudder Shaft Log,&Tail piece,do the rest of your thru hull wires connect there also?When I,removed these, the wires were connected to the zincs laying loose on the other end.I.had no idea where they went.You Have helped me a lot Thank You and all others.

[David M]

If there is no corrosion then there is no need for an anode. That's what it boils down to.

[rtbates]

BOND them... The only reason folks have no issue with NO BONDING is they happen to be in a 'clean' marina. By 'clean, I mean, no stray currents in the water from boats with suspect wiring. Dock beside one and your zinc can go away in months, IF bonded. IF NOT BONDED it'll be your thru hulls that go away.

[Matt Johnson]

Here is Westmarine's article about bonding (click here)

"
Bonding and Electrolytic Corrosion Due to Hot Marinas

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.

Your zinc is only intended to protect against the modest galvanic potentials and therefore currents that are caused by the dissimilar metals that are immersed and electrically connected together on your own boat. Your zinc is incapable of supplying enough galvanic potential to protect against substantial DC currents that may be flowing in the water. These DC currents in the water will cause electrolytic corrosion to your bonded thru-hulls or metal parts.

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."