Zinc question...

Chris Miller

Chris Miller

Sustaining Member
Hey all... Quick question from my Father in law about zincs: Will doubling up on zincs on the prop shaft last longer than a single? Or will 2 dissolve (or give up material) as fast as a single?
He's concerned about the longevity of his zinc since the boat was commissioned (first time) in August and when pulled in Nov had very little left. I haven't seen it, just relaying a question.
Thanks!
Chris

ps. He's going to have the dealer go over the electrical system to check for stray voltage.
 
E

Emerald

Moderator
Hi,


I will give you a 95% confidence level that, yes, two zincs will give you greater protection. I have also had several folks over the years advise me to use two zincs, one in front and one aft of the strut as a last resort safety catch if for some reason your coupling on the prop shaft goes, hopefully the leading zinc will keep the whole thing from shooting out the strut leaving a hole with lots of water coming in. The caution with putting a zinc in front of the strut is to make sure you have it far enough (let's say 4 inches or so) ahead of the strut bearing so you don't interfear with water flow into the strut bearing, which would cause overheating of the bearing.


-David
Independence 31
Emerald
 
G

Glyn Judson

Moderator
Moderator
Doubling up zincs

Just to keep things lively by opposing David's thoughts, I'd like to share with you my long-term experience with doubling up zincs and more. When I had my E31 to the west coast from South Carolina, it had a single collar zinc on the prop shaft forward of the strut (good idea David). A friend helping me paint the bottom suggested that I drill a 1/4" hole in the strut and add to dollar zincs. It sounded good to me so that's what I did. Hey, what do I know? I can't tel you the difference between an amp and an ohm. Fast forward to the next haul-out a couple of years later and all the bottom paint was burned off the hull right down to the gel coat around the strut base and a cintered bronze ground plate forward on the port side under the hanging locker. The area of exposed gel coat was about 3-4" in every direction away from the strut and plate. A quick, panicked phone consultation with my bottom service guys revealed that what I was looking at was the result of over zincing, what they called a "hot zinc" condition. They recomended removing one of the dollar zincs, reducing the count from three to two and observing the result. I did that, primed and repainted the burned areas and put the boat back in the water. A year later I had to haul out again. The burning was still there but about half of what it was with the three zincs. I removed the second dollar zinc, repainted, etc. and a year later there was no hint of burning. I'm now back to just the collar zinc on the prop shaft and all's well witht the world. Glyn
 
E

Emerald

Moderator
Hi Glyn,

This is really interesting. There's got to be a way to get scientific on this. We've got loads of stray voltage at our marina. I can take any piece of metal on the pier, put a meter on it, dangle the other end in the water and get a reading. I am trying to track down the offenders right now, but our dockmaster isn't interested, but that's another issue. So, what I found when I hauled my previous E-27, which was at the other end of the marina from my current slip, was "normal" zinc deterioration. This year when I hauled, and Emerald is now in what seems to be the "high voltage" section of our pier (I am now surrounded by folks who never ever move their boats or unplug shore power -true dock queens), there was barely enough material left on both zincs for them to even stay attached - I was able to rip one off by hand without touching the clamp screws.

So, someone must have some way to gauge the right amount of zinc other than the trial and error you and I have gone through.

I wish we didn't get so many blasted jelly fish in the Chesapeake so I could go anchor on a cove mid season and dive on her and see what was up :mad: - hate those jelly fish.....


-David
Independence 31
Emerald
 
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NateHanson

Sustaining Member
Do the jellies you guys get sting? We occasionally get a ton of moon jellies around us but they're non-stinging/non-tentacled.

You should be able to map your marina with a meter and an electrode (doesn't have to be zinc, just measure the voltage potential between the shorepower ground hole and the water). BE VERY CAREFUL WHEN STICKING A METER PROBE IN AN OUTLET!
 
N

NateHanson

Sustaining Member
Hmm. I just did some looking, and found that moon jellies DO sting, although I couldn't find out how irritating their stings are. I must admit I've never been tempted to jump in the water at our slip when the water is filled with these (or any other day for that matter), but I'd gotten the impression that they weren't really a hazard.
 
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NateHanson

Sustaining Member
Here, I found info backing up the general mildness of the moon jellies
Usually you can handle one without getting a sting (although some people do experience a short burning sensation).
Click to expand...

That's about our Moon jellies though.

From your link it sounds like you've got it worse with the Seanettles:
The jellyfish for which Chesapeake Bay is widely known in the summer is the Sea Nettle, Chrysaora quinquecirrha. It occurs from Cape Cod south along the U.S. East Coast, Caribbean and Gulf of Mexico, yet it abounds in Chesapeake Bay in numbers unequaled elsewhere. It occurs most abundantly in the tributaries of the middle Bay (salinities 10 - 20 ppt), where it is white in color. In the southern Bay, it often has red/maroon markings on the long central tentacles and on the swimming bell.

The Moon Jelly, Aurelia aurita, with its very mild sting that poses not threat to swimmers, also occurs in the southern portion of the Chesapeake Bay during the summer.
Click to expand...
 
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