How many zincs on an exposed shaft?

[Robin]

We need to replace the zincs on our new to us*boat before we relaunch, having had her stored ashore since we purchased last year.* The existing zincs are not really worn enough to replace, but then we hope not to have to lift out again for some time so it would be silly not to use the opportunity to change them.

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My question relates really to the shaft anodes and*we have two shafts each with two anodes fitted at present which are not even half worn away.* I have ordered 4 new anodes (plus all the others needed) but I'm wondering if we should just add an extra new one to each shaft and leave the existing ones in place as well?* Would 3 anodes per shaft cause a problem, or even four if we put all the new ones on?*

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Same with the big flat 12" x 6" anode on the transom, if there is enough bolt space is there any sense in adding the new zinc rather than just replacing it with a new one?

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I hate waste!

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[FF]

Wooden boats can be over zinced , which does cause problems.

A plastic boat would not have this problem.

 

[Robin]

I was more concerned about the extra waterflow disturbance and extra weight on a rotating shaft, maybe causing vibration or something?

 

[skipperdude]

Doesn't sound right to me . As zincs wear away they diminish in size and often wear unevenly. Never heard of an issue in that regard.

You can over zinc. A zinc oxide will form on your under water metal.

I don't think 2 zincs will cause that but one per shaft should be sufficient.

When they loose 1/2 there volume Then replace.

Do you know the history of when they were last replaced. A hot harbor or marina can cause the zincs to deplete rapidly.

SD

 

[Phil Fill]

At least once or twice a year have a diver check/clean the hull, running gear, though hulls and zincs.* Also ask boaters around you how fast their zincs go.* Some marinas you have to replace quite often.* The zincs that usually go the quickest is the small bow thruster zincs, then the shaft/rudder, and then the big main zincs.* Zincs devolope a white coating is shield the zinc.*
*
Most older zinc loops/connection do not protect as they are usually not maintained/clean/repaired.* So if you zincs do not get used is even worse as they are not protecting your boat.* The zinc protection loop, green wire that bonds/protects is one of the most important systems and the least know and repaired.

 

[Robin]

Thanks guys. The existing zincs are only part worn as we bought the boat about 7 months after they were replaced and immediately had it stored ashore as we went back to the UK. We are now having the yard add more bottom paint and we will fit new zincs because we are out of the water now and don't want to do more than diver cleans for a while, especially as I have just signed the order to do this. I'm in the wrong job because I need to be either an investment banker or a an antifouling paint applier!

We have some bubbly paint on the transom by the big anode there which I guess is caused by it, certainly our surveyor said so.

There are currently two barrel shaft anodes on each shaft, well spaced out, so I will replace those with new ones and just keep the part used ones as spares in case sometime we have a diver that hasn't got one when/if we need it.

Our surveyor checked the anode wiring over and apart from one connection pronounced it OK.

All this bonding is far more than we are used to doing in the past in the UK on sailboats, when we normally only protect the prop with a pear shaped anode connected to the engine and thus via the gearbox and shaft to the prop, and only had one on the prop itself if it was a folder rather than a fixed prop.

 

[Phil Fill]

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The bubble paint is cause because there is no connection to the zinc loop so the zinc in the *paint is used up. Its not to concerning but it should be looked at.* Last pull we had three area like that so I clean the bonding wire and make sure there was conductivity.* One was around a through hull that I took out, one was as the bottom of the shoe where the rudder rests, and the other was the gen set through hull.*I also installed a large Drivers Dream Zinc in the bow to protect the*bow thruster as the small zincs where the first to go.* Anyway that is what the yard and my diesel mechanic told me.*

** So I will have the diver keep a look out for areas.*

 

[psneeld]

The right amount of zinc is the right amount of zinc.

Unless you masure the underwater metal potential with a Silver/Silver Chloride half-cell sensor..you are only guessing.

Overzincing a wooden boat is serious...overzincing a glass boat USUALLY only causes bottom paint issues.

VERY common in northeast to see 2-3 zincs on each prop shaft...only usually a problem if one lets loose and takes out the others (not very common but have seen it)

Leaving zincs on that show about 1/3 wasting is penny foolish because on many zincs...the reactive zinc is gone both in what you do and don't see.* In the water you CAN measure to see how much they are protecting with the Silver/Silver Chloride half-cell sensor.

 

[Robin]

Thanks to all. I will replace all now since the opportunity is there and keep the old ones as emergency spares.

 

[FF]

I will replace all now since the opportunity is there and keep the old ones as emergency spares.


If you are spending on zincs , spend enough to avoid the Chinese garbage , if you want them to work.

 

[psneeld]

Robin wrote:
Thanks to all. I will replace all now since the opportunity is there and keep the old ones as emergency spares.

*Irf you are going to take them off...they aren't spares...they are now recyclables, trash. or possibly fishing weights.

If you need spares...but another set that will actually do something.

The first time you loose a $400 prop or worse due to galvanic corrosion for the want of a $10 zinc you'll wonder.

Not saying there's not a lot more to preventing galvanic corrosion but underwater metal with zinc on it at least has the first line of defense.

 

[Robin]

psneeld wrote:Robin wrote:
Thanks to all. I will replace all now since the opportunity is there and keep the old ones as emergency spares.

*Irf you are going to take them off...they aren't spares...they are now recyclables, trash. or possibly fishing weights.

If you need spares...but another set that will actually do something.

The first time you loose a $400 prop or worse due to galvanic corrosion for the want of a $10 zinc you'll wonder.

Not saying there's not a lot more to preventing galvanic corrosion but underwater metal with zinc on it at least has the first line of defense.

Understood, but these are really very little depleted. I spoke with the previous owners last night and they told me the zincs were just 5 months old.* The only reason the question arises is because we had the boat stored ashore immediately after our purchase survey whilst we returned to the UK, now we are getting back to the boat soon*and since she is out of the water it makes sense to do any underwater work before launching, including replacing the zincs.* We very probably don't need to put on more bottom paint either since it had two coats of Micron 66*5 months back.* However we are having the yard put two more coats of Micron 66*paint on plus I have already ordered a complete set of zincs.* It is just that it seems wasteful to just ditch the others!* We will be living on board and will not lift out again for some time if we can avoid it and just diver clean in between.

 

[skipperdude]

If the zincs are only 5 months old I would say keep them on .

If you are going to hire a diver to clean the hull it is not that big a deal to have them checked and replaced with the new ones when needed.

That way you won't be wasting the ones you say are practically new.

SD

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[psneeld]

Robin wrote:psneeld wrote:Robin wrote:
Thanks to all. I will replace all now since the opportunity is there and keep the old ones as emergency spares.

*Irf you are going to take them off...they aren't spares...they are now recyclables, trash. or possibly fishing weights.

If you need spares...but another set that will actually do something.

The first time you loose a $400 prop or worse due to galvanic corrosion for the want of a $10 zinc you'll wonder.

Not saying there's not a lot more to preventing galvanic corrosion but underwater metal with zinc on it at least has the first line of defense.

Understood, but these are really very little depleted. I spoke with the previous owners last night and they told me the zincs were just 5 months old.* The only reason the question arises is because we had the boat stored ashore immediately after our purchase survey whilst we returned to the UK, now we are getting back to the boat soon*and since she is out of the water it makes sense to do any underwater work before launching, including replacing the zincs.* We very probably don't need to put on more bottom paint either since it had two coats of Micron 66*5 months back.* However we are having the yard put two more coats of Micron 66*paint on plus I have already ordered a complete set of zincs.* It is just that it seems wasteful to just ditch the others!* We will be living on board and will not lift out again for some time if we can avoid it and just diver clean in between.

*

*If living aboard and having a diver check and replace zincs ...then I guess in your situation it would be OK...but you are as likely to need the diver for cleaning about the same time to change zincs...either the new ones or old ones...seems you may have jumped the gun...if you have no idea of zinc consumption...you are just guessing about a lot anyhow.

Some boaters*will tie a wire into the bonding system and hang a zinc over the side to lengthen the change interval.

 

[C lectric]

If you want spares then get new ones. The old ones will be good for weights in crab or prawn traps.
I put three on my shaft but I haul every two years. Next haulout They are still there but what is left isn't worth keeping except for weights somewhere.

Make sure they are installed properly or not only won't they do the job you expect but they will loosen and come off.
Mount them so the parting line from zinc to zinc is ~120o [for 3 zincs] lightly snug them, then hammer each half, snug up and hammer again a few good raps, untill no more slack is realized. Install them no closer to the cutless bearing than about a fist width or two zinc lengths..

Clean them. The contact surface of both the zinc and the shaft must be clean. I've mounted zincs and then tested after and found no contact untill I learned to sand. Lots of people don't do that including some pros.

Which reminds me, after installation check for continuity. You will at least be assured they will work at that time.

 

[skipperdude]

C lectric wrote:
Make sure they are installed properly or not only won't they do the job you expect but they will loosen and come off.
Mount them so the parting line from zinc to zinc is ~120o [for 3 zincs]

*Have you ever run into an issue of to much zincs. I had an issue with a boat next to me in a hot harbor and developed a zinc oxide coating on my prop and shaft.

He had more zincs than a battle ship he was of the mind that to much is not enough.

I actually had a white coating on my bronze propellar that would not come off. Looked like someone sprayed it with white spray paint.

SD