Zinc - Galvanic isolator

JohnShannon · Jun 12, 2014

Don't think so, the galvanic isolator is inserted in series with the ground wire of the AC line (which you don't have) and prevents currents flowing in the ground wire unless the driving voltage is higher than about 0.6V (as in a safety issue)

dparilla · Jun 12, 2014

JohnShannon said:
Don't think so, the galvanic isolator is inserted in series with the ground wire of the AC line (which you don't have) and prevents currents flowing in the ground wire unless the driving voltage is higher than about 0.6V (as in a safety issue)

True - a galvanic isolator only helps when connected to shore power.

Different bodies of water will act on zincs at different rates, sometimes even different ends of a marina will have different rates of consumption. When I am in Annapolis and the Chesapeake (with varying degrees of salinity), my zincs last only for the 3 months that I am on the bay, by August, they need to be replaced. Then in September when I schlep back to DC on the Potomac which is almost completely fresh water, my zincs will last through the entire winter.

Calif. Ted · Jun 12, 2014

Last time my boat was eating zincs that fast it was because of a leak from the AC supply for the entire dock. Could be another boat or the dockside supply but I would think it indicates an AC leak in the vicinity. My diver alerted me to the problem, they usually know when the zincs are going faster than they should.

fstbttms · Jun 12, 2014

A galvanic isolator will not help you if the boat is not plugged into the shorepower system. And contrary to most boat owner's beliefs, rapid zinc depletion is due most often to a problem aboard your own boat. Look there first for the cause.

Warren Milberg · Jun 12, 2014

While is not uncommon for marinas to have poorly grounded power posts on their docks, I agree with Fstbttms: I'd be looking for a DC leak on your own boat first.

frankies56 · Jun 12, 2014

galvanic zink

just a thought but could there possible be a steel boat close to where you are docking. my boatis always plug to shore power and notice no problems. just a thought

mitiempo · Jun 12, 2014

Richard19068 said:
I'll try to figure out how to test my boat for DC leaks.

Start with any wet wiring - like the bilge pump which is a common culprit or any connections low in the boat, engine possibly.

jibes138 · Jun 13, 2014

Remember the zinc is a sacrificial anode and this is a process like electroplating. The positively charged anode (zinc) gives up atoms that attach themselves to a cathode or negatively charged item. So the current path is from the zinc to a ground somewhere else. The zinc is at a higher electrical potential so this suggests that the previous posts recommending an electrical problem on your own boat as the likely culprit are a high probability of being correct. Acids will also react with metals and tend to dissolve them so you might want to also look at the PH of the water in the marina and see if it could be dissolving them chemically rather than electroplating. In the case of a chemistry issue higher temperatures tend to speed up reactions so you might see them dissolve faster in the summer months.

jibes138 · Jun 13, 2014

Richard19068 said:
Yes, I'll start with the bilge pump and high water alarm circuits since they're the only ones energized while in the slip. Jibes, interesting comment but if it was high PH everyone in the marina would have a similar accelerated burn rate right? I have a feeling I may be sacrificing zinc to the less than well maintained boat next to me but I don't know if that's possible with me not being plugged into the shore power. Thanks again.

It is a question of energy potentials. If.your zinc is at a higher potential then it will give up atoms. Since you are always connected via ground to your battery maybe the battery is discharging causing a higher potential in your zinc?

Charles Erwin · Jun 13, 2014

There is no chance the boat next door will have any effect on your boat. That is only possible if your boat is wired to the one next door.

Does your area have any dock structures/pilings made of steel? Are there any warning signs (Do not Anchor or Tie) on any nearby structures?

If there are no such nearby shore structures - then your zinc decay rate is almost certainly caused by something amiss on your boat.

Measure your boat hull potential and the answer will no longer be a theoretical answer.

As it is now everyone is necessarily guessing.

Charles

Stu Jackson · Jun 13, 2014

Charles is right. In addition to the helpful advice here, why not buy a book and read all about it? Really. It's too long to retype all the details which take up two or three pages and a couple of diagrams and two or more sidebars in Nigel Calder's Boatowners Manual for Mechanical & Electrical Systems. Everybody with a boat big enough to have an inboard engine should have this book anyway. As far as I know, there aren't any particular websites that have as good a description as Nigel's. If there are, I'd like to hear about them, with LINKS, and I'll add them to my Electrical 101 topic on our C34 board.

IH82BL8 · Jun 14, 2014

Does keeping the main battery switch turned off when not in use help slow/prevent zincs being eaten up?

Stu Jackson · Jun 14, 2014

Richard19068 said:
Thanks for the confirmation that an isolator probably won't help in this case.

I'll try to figure out how to test my boat for DC leaks. Lots out there on that but little consistency in the approach and advice.

Thanks again

An hour spent in a chandlery reading Nigel Calder's Boatowners Manual, better yet buying the book, would dispel a lot of the chatter. Really.

Good luck.

Charles Erwin · Jun 14, 2014

Typically the main battery switch involves two batteries (or two groups of batteries called banks) The main switch allows you to select which of the battery (banks) provides power to the boat systems.

Some parts of a boat electrical system may not shut off when the main battery switch is "Off." For example - some people wire a starter motor directly to a battery - just like in your car - or a bilge pump so that the bilge pump will operate even if the main switch is "Off". There are countless other examples of items that receive their DC power directly from the battery and do not pass through the main switch.

So - in order to tell if main switch "Off" means that no DC power can pass through a zinc and return to the battery you need an accurate as built electrical diagram - not a factory diagram. Means you have to do it yourself.

An alternative is to measure your hull potential twice -- compare main "On" to main "Off." Better even - all battery(s) disconnected compared with one or more battery(s) connected. You will see any electrical difference.

Likewise if there is any battery charging source or if shore power is engaged you need to account for these.

Charles

Stu Jackson · Jun 14, 2014

Charles is right again. Another book, by Charlie Wing, covers these switching arrangements on pages 61 & 62. We've also recorded them here:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

Poke around and learn what you have, 'cuz only YOU can tell us.

Another thing, perhaps mentioned earlier, is that bilge pump wiring is, well uhm, in the bilge, and often is found to be the first "usual suspect."

Good luck.

dparilla · Jun 14, 2014

Nigel Calder's books are simply exceptional in the scope of issues they address. Worth every penny, and available in e-book format as well as hard copy. I have 2 editions of the Mech/Electrical and 2 editions of the Marine Diesel Engines. Wing's book is also outstanding to reference.

Zinc - Galvanic isolator

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