Pencil Zinc life/degradation rate

[Mark Sutherland]

I just replaced my pencil zinc the other day.  The old zinc was a YEAR OLD and when I pulled it out, about 90% of the material was still intact.  (*Note, I waited a year because every 3 months that I checked it, it was good...).  In the past, my zincs have lasted 3 to 6 months.  I put about 50 hours on the engine last year.  Why would this zinc last so long?  Are there different kinds of zincs?  Did I use the wrong one?   

[Kevin Henderson]

HI Mark,

Have you moved within your marina at all?  or have others moved away from your slip.  I noticed this as well.  Last year when I was at another marina, I had noticed several of my neighbors were pretty bad at allowing their electrical shore cable to dip into the water.  Where I'm at now, no one around me allows their cables getting wet.  Additionally, If your neighbors are as routinely changing their zincs, your zinc is not the only one around that will be sacrificed.
 
I'm certain others here can give a much better explanation about zincs and the fact that a marina is essetnailly one giant battery as explained by Don Casy here:

http://www.boatus.com/boattech/casey/sacrificial-zincs.asp

That being said, when you changed your zinc last year I hope you did NOT put teflon tape on the threads for a seal.... Metal to metal is absolutely imperative.