I replace the shaft zinc each time the boat is hauled. Once every 2 years when I paint. I also do a quick haul each spring to clean the bottom and if it looks worn I will replace it then. We are in fresh water so it is probably overkill, but a zinc for the shaft is cheap.

Max-Prop recommends every year for the end cap zinc. I am new to the prop so I don't know how long it will last.

I would be curious to see how often people change the zinc anode in the heat exchanger. I don't put a ton of hours on the boat (approx 85hrs per year).

My heat exchanger pencil zinc wears by half about every 12 months, so I replace it annually.

The prop shaft zinc gets checked every time I dive the bottom for cleaning and replaced about every 10 months.

Wow, consider yourselves lucky. I change the prop shaft and heat exchanger zinc about every 3-4 months. I keep a bag of pencil zincs and a wrench in the aft cabin just so I don't have any excuses not to do it.

-Erik
#1939 (salt water)

Erik,

I too am in salt water, my zincs have been holding up for over a year on my shaft and two years on my pencil zincs. If you need to replace yours every three months my guess is you have an A/C wiring issue or someone around you does. If it is in the area it is called a hot spot and you may want your marina to check it out as it can eat up zincs quickly one and secondly could be an indication of a safety problem if someone is leaking A/C into the surrounding area.

There is some excellent info at this link regarding the subject: [url]www.boatus.com/seaworthy/galvanic/default.asp[/url]

Good points, Steve.

We never plug our boat in at the dock except once a year to exercise the AC unit. (in case anyone is wondering, our large solar panel array take care of our electrical needs). We also don't have anyone else using dock power within at least 100 yards of us, so we avoid the situations you describe.

I am not sure if this was brought up or not in the past. But if your in fresh water one needs to go with a Magnesium zinc instead of a true zinc. You can actually tell the difference with your eyes closed, as the Magnesium is way lighter then regular zinc.

In the past the old zinc's never really changed size or showed pitting. Then after I changed them out to Magnesium you could tell that they were doing there job in protecting the components.

Randy

Caprice is docked at my own dock in my backyard like Duane's. I do not have solar panals so if I don't use my boat for a week I plug it in to charge the batteries with no problem. Howevr, I notice my zinks dissolve faster sometimes when I go on a cruise and stop at some marinas.

Mike,

If you look at the linked article I posted it does cover the point that when you plug in at a marina if you do not have a isolation device in your A/C system, you become part of the electrolysis system of the boats around you pluged in as well.

DC leakage as noted in this article can also cause rapid wasting of zincs. In the plating process, such as chroming the process uses quite low voltages in a chemical/electrolite bath to transfer metal from anodes to the plated material. The plating process takes place over just a few hours. So even if you never plug into AC you can have rapid electrolysis from a DC leak.
After reading this article I am going to inspect the wires going to my bilge pump a bit closer as when it rains I do get water in the bilge. It sounds like a poorly insullated connector dangling in the bilge water is enough to cause problems.

Thanks or the link. I naively assumed that having the shore power cord connected, but having all the AC breakers "off" would somehow break the circuit. This is probably not the case. Perhaps I'll try leaving the cord unplugged as much as possible and see if that reduces the zinc eating.

I do have a galvanic isolator in the AC line, which theoretically, should limit the amount of current. Is there a way to test it? I'm not certain it's doing anything.... :)

-Erik

Steve
Yes, I did read the article which was great. Now I have another question.

Disimilar metals cause corrostion. Why do they put in and aluminum mast and connect it with a copper wire to a stainless steel bolt in a water gathering bilge and the bolt is attached in a lead keel?

That would be a auxilary battery, if you kill the main batteries you can slooooooooooly charge the main batteries using the mast battery. The voltage will increase if you fill the bilge with salt water.