T&T: Underwater Camera / Proper Shaft Zinc Installation

[Albin43SDtr]

John,

>I recently had a diver replace the zinc on my prop shaft. I
>would like to know if it is still on as they seem to have a
>habit of falling off.

If a shaft zinc falls off before being "eaten up", it was improperly installed.

Shaft zincs are made slightly smaller in diameter than the shaft, so 
that it naturally "grips" the shaft. Inside the two haves, (a 
quality) zinc will have small bronze buttons. These buttons serve to 
make good electrical contact with the shaft. When the mounting screws 
are first tightened, the buttons are not necessarily well seated, and 
the zinc probably is not up to the shaft all around. Several blows 
with a hammer on each side of the zinc will properly seat them. This 
pushes the entire zinc up against the shaft, and the bronze button up 
into the zinc after it hits the shaft, while the zinc conforms to the 
shape and size of the shaft. (Often, boat yards use sanders to remove 
old bottom paint/epoxy and or marine growth. This can make slight 
imperfections in the "roundness" of the the shaft.) The zinc's screws 
can then be tightened some more - often a lot. A couple more blows 
and a check to be sure that the screws are still tight will confirm 
proper mounting. The size of the shaft (and zincs) determines how 
hard the hammer blows have to be. The object is not to beat the 
zinc/shaft to death, but to simply seat it properly.

I routinely re-zinc my boats in the water, as well as when hauled. I 
have never lost a shaft or other zinc.


Take care and be safe.

Wayne
M/V Celestial
Albin43 Sundeck