Advice on placement of zincs, please

Hi,

Our E30+ came with 2 oval zincs placed about an inch apart on the drive shaft between the strut and the hull. There is no zinc on the bronze propeller or on the strut, or anywhere else (other than the pencil zinc in the heat exchanger).

Lately, I have seen or heard of sailors placing zincs on the strut itself, on the keel, on the end of the prop, and some only put one zinc on the prop shaft.

My question is: "What is the optimum correct placement of which kind of zinc on a 30 foot Ericson (or similar sailboat) in salt water? An explanation for the different placements mentioned above would also be interesting.

Thanks,
Frank

Frank,
On my 28 I have a zinc on the prop. shaft about 1 -2" before the strut. It works well in the salty warm waters of the Chesapeake.

Best Always,
Frank

Thanks, Frank/Bayhoss

So in our cool British Columbia/Northwest Pacific waters, I have to replace the two prop shaft zincs on our boat every 5 months. I'm guessing that they would wear even more quickly in warm water, like the Chesapeake--how often do you have to replace your single prop shaft zinc?

Frank

Two zinc or to over zinc, that is the question.

Frank, When finally getting our E31 trucked out to SoCal from Port Royal, South Carolina back in June of 1995 and into the local boat yard here, I too wondered about the whole mystery of how much to zinc the boat. There was a collar zinc on the 1" prop shaft and that was it. Another friend who was helping with the bottom paint, etc, suggested that I add two more, a sand dollar zinc on either side of the strut and that I did by drilling a 1/4" hole and mounting them. Fast forward a year or so and when hauling for some reason that's long slipped my memory, I was horrified to discover that two areas of the hull were devoid of bottom paint for a distance of 2 to 3 inches around. They were the strut as it entered the hull and a sintered bronze ground plate forward on the port side and bolted through the bottom of the hanging locker. What in the heck had happened? There was no sign of that when I applied the new bottom paint to the hull back in the summer of 1995. A quick call to my dive service cleared everything up, I was "too hot" with too many zinc's. What in the world did all that mean? I had no idea but bowed to those much wiser than I and took their advice which was to remove one of the sand dollar zinc's. That I did and our boat went back into the drink for another period of time, say...two years. Actually I really can't remember all that clearly how long but suffice it to say, it was longer than an additional year. With the boat again out of the water for reasons again I can't recall, my primary interest was in checking for that burning before anything else. Sure enough, there it was, the burning on both the strut and the ground plate again but to a much lesser degree, let's say only 1" around both. Ok, enough with this little science experiment, I took the other zinc off the strut and went back to what she'd had in the first place, just the one on the shaft. To this day, there is no burning in either place or anywhere else for that matter. What's the lesson her for you though? That's hard to say other than to adopt the philosophy that if it ain't broke, don't fix it. Well, that doesn't exactly apply here because there's noting broken on your boat but you get the idea. How about letting sleeping dogs lie? No that doesn't work either. I know, talk to local a dive service and get their opinion on the subject of being over zinced and the possibility of that burning I experienced from too many of them. Could it be that colder water is more kind to a zinc or are we talking strictly electrolysis in any temperature, etc? Had you considered removing one of the two as is the case now with our boat? Shoot, I don't know if any of what I wrote above has helped but good luck anyhow and please share the result of any answers or opinions you come up with in your research. Glyn Judson, E31 hull #55, Marina del Rey, CA

Zinc's again.

Frank, I didn't see your most recent post about replacing them every five months. That's about in the ball park for our boat, maybe every six months but close enough. I can tell you that my dive service tells me that they should lose only about half their size before they need to be replaced. What do yours look like after five months? Glyn

Glyn,

Thanks for your detailed reply, and your reminder to not fix what isn't broken (I have a bad habit of trying to get everything just right, and sometimes end up causing a problem that I wouldn't have had if I just left everything alone in the first place).

The two zincs on my prop shaft will last 6 months if I push it, but then they only have about 1/3 or even 20% left, and once one of them had fallen off as the area around the bolt had worn away, so I usually replace them at 5 months to ensure I maintain protection. After 5 months there is still quite a bit left, maybe half, but they are clearly wearing.

Although the two zincs wear a bit faster than I would like (Don Casey recommends replacing zincs annually, so clearly he doesn't live in my marina!), I am not experiencing any visible electrolysis on my bronze propeller, strut or through hulls.

I also don't know what the difference would be if I used collar zincs rather than oval zincs--how do people decide?

Frank

Frank, I replace every six months. I use the oval zincs. Seems to be working ok.

Best Always,
Frank

When I had the bottom done about two years ago the yard added a zinc like Glyn described to the strut. I didn't ask them to but I figured, what the heck. Previously it only had the collar zinc on the shaft; now it has both. I don't understand how it is possible to be "over-zinced." If the theory is that the zinc sacrifices itself to protect the other metals, it seems that more zinc would just take longer to erode.

My diver hasn't mentioned anything about unusual deterioration below the waterline and he is usually good about letting me know if something needs attention.

Help, I'm zincing!

Mark, snip>> I don't understand how it is possible to be "over-zinced." Hey, don't ask me, I just know what I saw and when relating it to my dive service on the phone, they zeroed right in on it. In the long run after a period of time measured in years, I was back to what I had in the first place with antifouling paint on every speck of the bottom. Ya 'gotta love it. Glyn

I did a web search and apparently it is possible to "over-zinc" the boat, resulting in the symptoms you described. Who knew...

Hot boat?

Hi Frank,
I'm amazed that you go through zincs that fast! I'm at the Yacht Club right next to where I believe you keep your boat, and shaft zincs easily last a year. I didn't haul last year but my diver scrubbed and checked zinc that was on from the previous year and said it was only about a quarter gone...I put on another one anyway.
Sounds like there might be a lot of "stray current" at the marina?

Hi,

Yes, I'm at the H dock of Townsite marina, and we have several live-aboards which may be contributing to stray current, though I'm not sure of this. I have talked with others, and they also report zincs only lasting about 5 months. I have spoken with the marina manager who is generally good and conscientious, but he denies any problem. As long as it only means more frequent zinc replacement, I can live with that. But I still want to ensure I have the right type and number of zincs.

Can someone explain the difference in oval versus donut-shaped zincs, when to use one or the other, or is this just a matter of availability and habit?

Thanks,
Frank

mherrcat said:

I did a web search and apparently it is possible to "over-zinc" the boat, resulting in the symptoms you described. Who knew...

Click to expand...

I see this all the time but owners often think more is better. Just the other day a guy at the yard had FOUR oval zincs on his Pearson shaft. I mentioned to him that he was running a risk of an over zinc situation but he did not care and has he said (there all gone by July so I need more)..... They're all gone by July for a reason....

He also had them half way between the strut and hull which can cause tremendous vibration potential when they start eroding and wearing unevenly. It's like throwing a tire wheel weigh smack dab in the middle of a jump rope.

One zinc about two fingers from the strut usually optimal for most boats. Keep in mind that there are really only three potentials on boats for underwater metals:

Eroding, Protected & Over Protected. You ideally want to aim for "protected"..

Thanks, Maine Sail.

Based on your recommendation, I'm considering going with one oval zinc placed between the strut and the hull, about two fingers from the strut. Aside from the zinc possibly wearing more quickly than the two zincs I have been using, is there any way to tell if one will be enough--ie. how can one tell if there is enough zinc, too little or too much?

Thanks again for taking the time to reply.

Frank