Newbie Question About Zincs

[off-the-grid]

I recently had someone tell me that the purpose of zincs was to protect you from stray current in marinas. And that you really don't need to worry about changing them when staying on the hook.

Is there any truth to this?

Up until I heard that, I was under the impression that they protect you anytime you're in the water...especially salt water, because there's always going to be a little current, at least enough to deteriorate the metal in heat exchangers, props, etc.

[bstreep]

Unless there's a problem with YOUR boat, your zincs will generally last way longer on the hook than at a marina. However, that's no reason to ignore them. Ours last about 1.5 years in the marina. We have friends on the next pier over that have to change theirs every couple of months.

[S/V_Surya]

Wish it were true. Cause is galvanic action between disimilar metals. Marina can make it worse but being on hook will not stop it.

[Tellie]

Zincs are intended to be sacrificial in an environment of dis-similar metals in water, especially salt water. You will go through zincs on the hook as well. Stray current in marinas can eat a zinc a lot faster that on the hook. Even on the hook if your ship has electrical problems you can still eat up the zincs fairly quick. Always check your zincs regardless of whether tied to the dock or on the hook.

[markpierce]

Originally Posted by bstreep

We have friends on the next pier over that have to change theirs every couple of months.

Sheesh! Have they considered installing bigger/additional zincs?

[David M]

Actually, this is two different topics which frequently get confused. This is because the source of the cause of the corrosion is very different although the damage can be identical.

The anodes on your boat protect the galvanically weakest metal on your boat by the zinc anode becoming the galvanically weakest metal on your boat. The zinc literally becomes the sacrificial anode. This protective effect occurs whether or not you are tied to the dock or at anchor.

The effect of being tied to shore power or having stray currents in your marina dissolving the metals on your boat is different. There are a number of ways to prevent this damage from occurring. It is a very involved discussion. The solution to this problem really depends on if and how your boat is being affected by internal or external electrical sources.

[off-the-grid]

Originally Posted by markpierce

Sheesh! Have they considered installing bigger/additional zincs?

I heard of a guy at my last marina who was going through them even more frequently than that. Like monthly.

David can't that second one really be out of you hands, depending on the marina, and the problem potentially being with their ****** electric or coming from a another boat near by? Not that I'll have to worry about that again, for at least 6 months.

[RainDog]

Originally Posted by grunzster

you really don't need to worry about changing them when staying on the hook.

"Damage" to the Zinc prevents "damage" to other metals on your boat. If you do not need them, they will never decrease in size, so will not need to be changed anyway. If they are decreasing in size, that means they are actually protecting your boat, so are indeed needed.

[hummingway]

Originally Posted by grunzster

I heard of a guy at my last marina who was going through them even more frequently than that. Like monthly.

David can't that second one really be out of you hands, depending on the marina, and the problem potentially being with their ****** electric or coming from a another boat near by? Not that I'll have to worry about that again, for at least 6 months.

That's what I hear. I have often see people allowing there shorepower to dip into the water. Given the field around any electric wire I wouldn't do it and I presume when someone does it effects everyone. Given that most dock don't seem especially well maintained it would seem likely that their wires are draping as well as the boards drooping. More power in the sea. I gave up the marina at the beginning of the summer so I guess I'll see what difference it makes.

[fstbttms]

Originally Posted by RainDog

If you do not need them, they will never decrease in size, so will not need to be changed anyway.

Not neccessarily true. Zincs that are not making good electrical contact with the item (theoretically) being protected may not deplete. Never assume they are doing their job. "Eyes on" is the only way top be sure.

[osirissail]

For marina electrical problems they invented galvanic isolators for your "ground" lead on your shore power cord. Or if you are really serious, a full isolation transformer totally keeps your boat's electrical system isolated from the marina's.
- - For above average galvanic problems in the boat, larger zincs work fine to increase the time between zinc replacements. Also the zincs in your heat exchangers are very critical to the health and longevity of your engine. Some heat exchangers are electrically isolated from the main engine block by gaskets and rubber mounts so I use a small jumper grounding strap to be sure the heat exchanger is electrically tied to the main engine block which is then electrically tied to the main zincs.