How to diagnose cause of going through anodes too quickly?

[josrulz]

Hi all,
OK, so obviously I'm no electrical guru. Please hang with me while I learn this one. As is obvious from the title of the thread, we're going through anodes (zinc) somewhat quickly. We put 2 zinc on the shaft in spring, and they need to be replaced in less than 2 months. This has been consistent over the last couple of years since we bought the boat. The good news is, the zincs do their job.

A bit about the boat: No battery charger, so we're never hooked up to shore power. I mean never. Like 3 days in 2009 was it. Our electrical system is simple: 2 batteries, one in each "bank", no refrigeration or AC, just lights, stereo, VHF, GPS, and radar. Metal hardware is bonded (was done by Sabre factory)

So while I realize going through zincs in a couple months isn't an emergency, I'd like to know why, in case there's something I can do about it.

Any suggestions on how to diagnose? Specific items I should check? Is it possible this is because of a neighbor, or is that out of the question because we're not connected via shore power?
Thanks,
J

[SlowButSteady]

Your boat could be acting as a "bridge" between two other boats, or between a "hot" boat and some other ground. This can be a problem if your underwater fittings are all bonded together; the electrical path through you boat's bonding system will have less resistance than the surrounding seawater.

You might be able to detect a bit of voltage by using a multimeter and some long probe wires. Put one wire in the water at the bow of the boat, and one in the water at the stern and connected the multimeter between them (using its most sensitive setting). Check for both AC and DC voltage. Try the same thing with the wires on either side of the boat. Alternatively, you can find a convenient place in the bonding system to insert the multimeter and look for voltage that way (but you may just get a reading from the galvanic potential between dissimilar metals in the circuit).

[AdamLein]

I think that for galvanic corrosion to occur you need three things:

1) dissimilar metals
2) immersed in an electrolyte
3) electrically connected

If you have no shore power connection, then the only things that your zincs can be electrically connected to are other parts of your boat.

[Tempest]

Sabres seem to be notorious for eating zincs. I've had the same problem with mine. Last year I put 2 on the shaft and one on the max prop.

Made it through the season with about 1/2 one left on the shaft..but I got in the water late in the season.

[josrulz]

So maybe there's not much I can do about it, if other S34s have similar problems. I don't mind changing the zincs, really, but as we start to add to the electrical system, I'd like what's there to be healthy.

When we add a battery charger, we'll include a decent galvanic isolator along with it, so hopefully, hooking up to shore power won't accelerate the eating of zincs.

We'll see.

Thanks for all the responses, folks.
-J

[tdw]

Originally Posted by josrulz

So maybe there's not much I can do about it, if other S34s have similar problems. I don't mind changing the zincs, really, but as we start to add to the electrical system, I'd like what's there to be healthy.

When we add a battery charger, we'll include a decent galvanic isolator along with it, so hopefully, hooking up to shore power won't accelerate the eating of zincs.

We'll see.

Thanks for all the responses, folks.
-J

Come on now. Going through anodes in two months ? I don't care how hard on anodes Sabres are supposed to be, it is not healthy to be going through them in only a couple of months.

[TropicCat]

This is a mystery. Zincs are purposely placed within a circuit to erode before anything important does. The current in this circuit is the catalyst for the erosion. From what the OP posted, he doesn't have a circuit. A conundrum for sure.

The OP didn't mention if he was in salt water. What if the marina has defective wiring and salt water is conducting the current to his boat? I'd say .. change slips and see what effect this has on the problem.

Just an idea...

[josrulz]

We're in brackish water, more or less. On the South River, just south of the Severn River and Annapolis.

Yes, it could be something about the marina or another boar. So that's why I'm asking how I could diagnose what the problem actually is, especially since I'm not connected to shore power. If it's something about our boat, I'd like to fix it. If it's someone else, then it would at least be good to know.

[tdw]

hmm.. finding the cause is the hard part unless it is an obvious wiring fault in the boat itself. I'm guessing a neighbouring boat or two but thats only a guess.

On Raven we had our forward hull anode (she's steel) start to erode at double time. I never did track down whether it was another boat (there was a bit of a steel clunker nearby) or a piece of stray wiring from the anchor windlass I was rebuilding at the time. When we lifted her again the anode had gone back to normal erosion.

You could of course hang an anode or two over the side when you are berthed. This could/should help preserve your fitted.

[SlowButSteady]

Originally Posted by josrulz

We're in brackish water, more or less. On the South River, just south of the Severn River and Annapolis.

Yes, it could be something about the marina or another boar. So that's why I'm asking how I could diagnose what the problem actually is, especially since I'm not connected to shore power. If it's something about our boat, I'd like to fix it. If it's someone else, then it would at least be good to know.

Try the multimeter trick I posted above. It may, or may not, work (you may need a pretty sensitive meter to get a reading). But, a positive result will at least give you an idea as to the cause. Alternatively, you could ask the marina for a different slip (if one is available). If moving the boat slows the zinc wasting, it's a good bet that you've been the victim of stray current from other boats; if it stays the same, there may well be some problem with dissimilar metals on your boat.