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Old 03-11-2011, 18:04   #1
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Zincs

Quick electrical question. I have a large zinc over the side and clamped to back stay on a Pearson 323. Will the zinc corrode even if not well connected to my boat. Or does zinc corrosion mean it is actually protecting my boat?
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Old 03-11-2011, 18:12   #2
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Re: Zincs

If it's corroding, it's doing its job.
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Old 03-11-2011, 22:09   #3
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Re: Zincs

It is doing nothing if not in direct electrical connection with the item (supposedly) being protected. To what is your backstay wired?
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Old 03-11-2011, 22:24   #4
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Re: Zincs

Unless it's attached to another type of metal under the water, it'll just corrode away naturally. >> Cathodic Protection 101
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Old 04-11-2011, 03:35   #5
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Re: Zincs

So my simple question is,Is corroding good or not??
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Old 04-11-2011, 04:28   #6
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Re: Zincs

Marvelpitt,
The simplest answer would be if the zinc is around the shaft, yes corrosion is good.

In the OP's case, the zinc is in the water, connected with a wire to the backstay.
If the backstay is connected to the grounding circuit of the under water metals on the boat then corrosion of the zinc would also be good (protecting).
If the zinc is not connected to any under water metals, then the zinc will still corrode but will not be protecting the boats underwater metals.

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Old 04-11-2011, 05:56   #7
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The boat wiring diagram from 1982 shows the back stay as part of the bonding system. But I guess the best way to phrase my question is will the zinc corrode anyway Or does it take a circuit and being connected to my boats bonding system. Thanks for all the hits to this thread!
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Old 04-11-2011, 05:59   #8
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Re: Zincs

Corrosion is great. The proper term is a" sacrificial anode". Its supposed to be sacrificed to prevent electrical corrosion of the other metals on your boat. It will not protect the other metals if there isn't proper electrical connection in place. In other words no loose joints.

Check your connections to be safe.
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Old 10-11-2011, 05:55   #9
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Re: Zincs

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If it's corroding, it's doing its job.
Oh not its not!

Why would you connect a zinc to your rig, for God's sake?

Ridiculous!

What you're trying to protect are underwater metals that might corrode through galvanic or self or electrolytic corrosion. Typically in your kind of sailboat this would be the propeller and shaft. A shaft anode is the usual means of protection, although as a fix it is far from perfect (the anode wears out, and loses its bond to the shaft, so stops working).

Get rid of it.
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Old 10-11-2011, 07:06   #10
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Re: Zincs

It will corrode, but not protect, when not connected.

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Old 10-11-2011, 08:14   #11
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Re: Zincs

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Oh not its not!

Why would you connect a zinc to your rig, for God's sake?

Ridiculous!
Because if the rig is bonded to the engine (as is the case in some models), an anode attached to the rig but hanging in the water will provide protection. I do not personally advocate this but in theory, it works.
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Old 10-11-2011, 15:00   #12
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Re: Zincs

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Because if the rig is bonded to the engine (as is the case in some models), an anode attached to the rig but hanging in the water will provide protection. I do not personally advocate this but in theory, it works.
Protection for what? The engine? And in any case why not simply connect the anode to the engine block and be done with it.

No. What we're primarily interested in is the running gear (prop, shaft etc). If you're running a flexible coupling for instance, there will be no connection, and no protection. And relying on the gearbox to provide a proper electrical connection (remember there's insulating oil in there), can be risky. I have known instances of pitting on gear trains through this method.

The ONLY 100% effective and reliable way to provide cathodic protection is to use a shaft strap connected directly to an underwater anode and the vessel's bonding system, if it has one. Even these can be unreliable if not installed and maintained correctly - although those sold by Marina Protection Systems in Australia seem to work OK. I have one as I have a wooden boat, and therefore need to control the amount of cathodic protection very, very carefully. (But that's another can of worms!).
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Old 10-11-2011, 15:43   #13
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Re: Zincs

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Protection for what? The engine? And in any case why not simply connect the anode to the engine block and be done with it.

No. What we're primarily interested in is the running gear (prop, shaft etc). If you're running a flexible coupling for instance, there will be no connection, and no protection. And relying on the gearbox to provide a proper electrical connection (remember there's insulating oil in there), can be risky. I have known instances of pitting on gear trains through this method.

The ONLY 100% effective and reliable way to provide cathodic protection is to use a shaft strap connected directly to an underwater anode and the vessel's bonding system, if it has one. Even these can be unreliable if not installed and maintained correctly - although those sold by Marina Protection Systems in Australia seem to work OK. I have one as I have a wooden boat, and therefore need to control the amount of cathodic protection very, very carefully. (But that's another can of worms!).
As the old saying goes...there's more than one way to skin a cat. ANY cathodic protection will work if you measure the potential and it's withing recmmendations.. With the right tool it's not that hard and you can see if your underwater metal is properly protected. But saying one way is the only way is just rubbish.
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Old 10-11-2011, 16:16   #14
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Re: Zincs

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As the old saying goes...there's more than one way to skin a cat. ANY cathodic protection will work if you measure the potential and it's withing recmmendations.. With the right tool it's not that hard and you can see if your underwater metal is properly protected. But saying one way is the only way is just rubbish.
I didn't say it was the only way to provide protection, of sorts. Just after decades of experience providing advice on cathodic protection, its the ONLY one that appears to offer reliability and effectiveness. Shaft anodes aren't bad - but I can send you photos of a prop shaft I removed from a boat that was almost completely wasted, with several shaft anodes still hanging off it. The problem is they corrode from the INSIDE as well as the outside, lose connection with the metal they are supposed to be protecting, and stop working. Sometimes you can hear them rattling on the shaft when motoring...

Bonding via the engine block and gearbox I covered in an earlier post, so that's not a reliable option.

I do have 'the right tool' - a silver/silver choride half cell tester for measuring impressed voltage - but I don't know anyone else who does. Or knows how to interpret the measurements. I've seen many wooden boats stuffed through over-protection than under-protection, for example. Excess zinc in a glass boat will merely result in the paint blowing off the protected surfaces. In a wood boat it can cause alkali delignification, which causes massive damage to the wood surrounding the protected metal, which can be very expensive to fix - sometimes resulting in the premature demise of the entire yacht. In fact zinc will ALWAYS overprotect a wooden boat, and there are other alloys that work more safely.

So it's not simply a matter of hanging a zinc any which way. Proper mechanical and electrical design is imperative to correct operation. If you can tell me a way other than a shaft strap that offers complete reliability for cathodic protection for underwater running gear, then I'll eat my shorts...
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Old 10-11-2011, 16:24   #15
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Re: Zincs

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Originally Posted by centralyachts View Post
I didn't say it was the only way to provide protection, of sorts. Just after decades of experience providing advice on cathodic protection, its the ONLY one that appears to offer reliability and effectiveness. Shaft anodes aren't bad - but I can send you photos of a prop shaft I removed from a boat that was almost completely wasted, with several shaft anodes still hanging off it. The problem is they corrode from the INSIDE as well as the outside, lose connection with the metal they are supposed to be protecting, and stop working. Sometimes you can hear them rattling on the shaft when motoring...

Bonding via the engine block and gearbox I covered in an earlier post, so that's not a reliable option.

I do have 'the right tool' - a silver/silver choride half cell tester for measuring impressed voltage - but I don't know anyone else who does. Or knows how to interpret the measurements. I've seen many wooden boats stuffed through over-protection than under-protection, for example. Excess zinc in a glass boat will merely result in the paint blowing off the protected surfaces. In a wood boat it can cause alkali delignification, which causes massive damage to the wood surrounding the protected metal, which can be very expensive to fix - sometimes resulting in the premature demise of the entire yacht. In fact zinc will ALWAYS overprotect a wooden boat, and there are other alloys that work more safely.

So it's not simply a matter of hanging a zinc any which way. Proper mechanical and electrical design is imperative to correct operation. If you can tell me a way other than a shaft strap that offers complete reliability for cathodic protection for underwater running gear, then I'll eat my shorts...

Eat away...plus I have a silver/silver choride half cell tester too...and have been giving advice and resolving zinc protection problems for decades too.

Again...you can hang zinc from the shrouds IF you have continuity and the potential is correct...a BIG if I do admit...I just don't agree with many in the marine business that are always saying "their" way is the correct way...too many variables...and very few exerts including me.
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