More Zincs?

[lehighsail]

I was reading about the bag of pennies and have what might be another dumb question.

At the end of last season my prop shaft zinc was almost totally gone. Should I consider having two zincs on the shaft this year. Does it work like that?

Thanks.

 

[Don S/V ILLusion]

Adding zinc is only the proverbial. "Band Aid". In most cases, people put two on just in case one somehow falls off. If you have an electrolysis problem, two will get eaten as quickly as one and in certain cases, can make it worse. There is a long explanation for this in the archives so I won't bother re-typing it.

What I'd suggest you do is identify what is causing the problem; the steps are well covered in the archives but feel free to ask if you don't find the procedure you should try.

 

[Bill Roosa]

You say that like it is a bad thing

I'd point out that they are called sacrificial zincs for a reason. There are many aspects to this that you cannot control so the fact that they rusted off and not your $3000 folding prop is a good thing don't you think?

 

[Witzend]

I keep her in slightly brackish water (only maybe in a dry August) otherwise fresh, on a mooring (w/solar charger). One normal sized shaft zink on a 1" bronze shaft will be ~50% gone in a season. I think the reaction will accelerate if you are in a marina with free electrons in the vicinity due to submerged power cords combined with improper AC wiring aboard. Some of the Zincs have a copper Bee-Bee that provides a better electrical connection to the shaft. This would seem like a good idea, but if you clean the shaft with sandpaper where you install the zinc the Bee-Bee may not really matter.
Other may have more data on the Bee-Bee design as it relates to a bronze or SS drive shaft.

 

[Maine Sail]

Before the zinc in the penny could become "sacrificial" the copper would need to get eaten away first, not likely.. Considering that the copper is a lot less anodic than the zinc in your manganese bronze prop then you won't achieve any anodic benefit..

This certainly has to be a mid-winter joke..?

 

[alexco38]

May be a few feet of lead pipes would work too! How about a bag of used battery plates?

The Anode cost a few bucks at Worst Marine at ransom prices. How much are you saving by using bag of pennies instead?

 

[JVB]

Read this primer on anodes
www.boatzincs.com/corrosion-reference-electrode.html
and these:
www.boatzincs.com/pdfs/Chart_A-Which_Anodes_Should_I_Use.pdf and
www.boatzincs.com/pdfs/Chart_B-Which_Anodes_Should_I_Use.pdf
You will find that zinc is not always the best anode material and that overdoing the amount of anode is bad too.

By the way zinc battery plates will work just as well as anything else made of zinc. It's chemistry not shape or beauty that counts here. If you really want to get into the subject here's a place to start on what is called "the chemical activity of metals":
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch9/activity.php

 

[Liam]

Have a diver repace the zinc mid-season.
I am in a "hot" harbor. A zinc on my boat only lasts about 3 months. I have a diver who is scheduled to change the zinc every 2 months. He charges $25 and does it when he is doing a bottom job for someone else on the dock anyway so it's no big deal.