Question about Zincs

#1

Since joining this site, I've been made more aware of the importance of zincs to protect our aluminum hulls.
I've had a 3x6x5/8 zinc bolted to my transom for at least 10 years and have noticed that it's not dissolving like the zincs on my OB motor.
So I checked it to see if it was making contact with the hull surface.
Using an ohm meter, I've discovered that the surface of this old zinc was non-conductive when holding the probes on the surface. It seems as if the zinc had formed an insulating surface on it.
My question is: Is this a common occurrence with zincs in general or a sign of a low quality or incorrect alloy blend zinc?
This is a trailer boat. The brand is Marshall Mfg.

Back view of the zinc

Close up of the surface. Counter bored the back to clear the mtg. stud washer

This how I have it installed. Thru bolted threaded rod which is conducting to the hull with nylon lock nuts with flat washers.

Rejuvenated zinc (cut the top surface to expose fresh zinc and ground all other surfaces)
and used lock washers to dig into the surface and annually check for continuity.

#2

Good job on the zinc repair and thank you for passing on some very useful know how.

Your thru hull looks a little dried out though.

#3

It's a good idea (especially for trailer boats) to give the zinc a good hard wire brush every now and again. Zincs can form a "skin" and loose some effectiveness.

On a boat that remains in saltwater you want to see the zinc dissappearing - means its doing its job! Freshwater and trailer boats can have the same zinc for years and years...

Great photos and solution....

#4

Great Tip Jay!!!!

That goes for the engine zincs as well

#5

welder wrote:Good job on the zinc repair and thank you for passing on some very useful know how.

Your thru hull looks a little dried out though.

It's funny how your pictures get studied by the other members.

You are right about my thru hull. You would not believe how many times I've looked at it and questioned it's strength.
The good thing about it is there isn't any load on it because there's PVC piping glued to the inlet side of it and locked in place, so no movement or side load occurs.

#6

I had heard somewhere not to use wire brushes on Zincs, but instead to use sandpaper because the wire brush has some negative effect on the metal. Can anyone comment on if this is true or not? I guess it is safer just to use sandpaper, but I am curious if anyone knows the science behind this, if there is any.

http://www.youtube.com/user/BLM26CC · #7

I heard.......(why be, there so many mysteries??)

That you use a clean wire brush aka: brand new, and don't use it for anything else but zinc cleaning.

Supposively because you do not want any other metal tid bits being ground into your zinc, from other wire brush tasks that your brush may have encountered.

How true this is the great unknown, but sure sounds like an adequate explaination to me. Cuz I just don't know much about metalergy (

) or is that chemistry (

)

I've also read this, "Clean zincs with a stainless steel wire or bristle brush. Do not use a common mild steel wire brush."

#8

a STAINLESS STEEL wire brush that you dedicate to zinc cleaning only - dat be da' rule!

http://www.youtube.com/user/BLM26CC · #9

Hmmmmmm, heard that somewhere

Ironwood Boats · #10

Hi

You can try dielectric grease on the bolts and a little where the zinc touches the aluminum.

You did the right thing by testing with an ohm meter.

I don't recommend Tef-Gel here because it does not conduct electricity.

Sincerely
John
Ironwood Boats.