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Larry

"claus" wrote in news:1YOdnS4xRIdBtHLZnZ2dnUVZ_q-
:

The problem is that the 3 small zincs erode rapidly - sometimes within 2
months - and sometimes within 4 months...no regular pattern.

The other zincs (1 and 2) look brand new after 2 years in the water and
obviously do not protect the propellor at all.

I'd bet the screw is electrically isolated from the saildrive, but I don't
see how. The little zincs are then consumed protecting, by themselves, the
metal of the screw, with no help from the big zincs on the shaft/drive
itself.

It would be impossible to test this without hauling the boat out and taking
a meter between screw and shaft.

If the marina or that derelict next door were the problem, it would eat
away ALL the zincs, not just the little ones on the screw.

There has got to be some way the screw is isolated, electrically, from the
other zincs. Does the saildrive have a rubber damper in the hub of the
screw? That would isolate it, right there.

--
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You can tell because none of them ever called Earth.