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b-rad 29-10-2009 04:34

Where to Put Zinc on Prop Shaft?
Im finaly done with my out of the water projects, all I have left is to put a zinc on before the boat goes swiming on friday. Is there a reason Not to put the zinc bewteen the strut and the hull? The zinc I got is about 2.5 inchs long and wont fit between the prop and the strut.

Zanshin 29-10-2009 04:57

There is a good reason to do so - if, for some reason, your prop shaft gets separated from your transmission then a bolted on zinc forward of the strut might just keep the shaft from dropping off the boat.

GordMay 29-10-2009 05:34

1 Attachment(s)
Zinc shaft anodes are often placed forward of the strut, because of the limited exposed shaft distance between the strut bearing & propeller hub (see ĎDí in diagram).
Donít place the zinc hard against the strut, which would block lubricating water flow through the bearing.

Portobello 29-10-2009 05:55

...and if your motor has soft mountings there is considerable movement of the shaft forward and backward as the motor moves. Leave space for this movement.

svHyLyte 29-10-2009 06:19

The zinc should be placed just a few inches forward of the strut, leaving only enough room between the strut and the zinc to allow water flow through your cutlass bearing. The density of zinc's is not uniform and if mounted midway between the strut and shaft log (where the shaft penetrates the hull) may have a tendancy to cause the shaft to vibrate in the manner of an unbalanced tire, particularly if there is a fairly long run between hull and strut. We discovered this on our old Cal 2-29 and found the same to be true on our First 42. Also, ensure that there is a good metal to metal contact between the zinc and the shaft.


GordMay 29-10-2009 07:12


Originally Posted by svHyLyte (Post 353870)
The zinc should be placed just a few inches forward of the strut, leaving only enough room between the strut and the zinc to allow water flow through your cutlass bearing...

Or even less.
I'd think about 1/2 (or even 1/4) shaft diameter to be sufficient.

Cheechako 29-10-2009 08:26

Boy.... I bet it feels good to be down to putting the zinc on and knowing you got it all buttened up correctly......... and of course getting her wet!

sailvayu 29-10-2009 08:37

The others are correct about placement but I will add polish the shaft under the zinc with a scotch pad prior to putting the zinc on and before the final tightening of the screws tap it on both sides with a hammer and then re-tighten the screws.

Enjoy floating again:)

Wayne Canning, AMS

David M 29-10-2009 08:53

Purely from an electrical standpoint, it makes no difference. Mechanically, it can. I put mine a couple inches ahead of the strut to make sure the cutlass bearing has proper water flow.

Solitude 29-10-2009 09:23

You may want to put 2 of those on. How many were on before, how long were they on, and how did they look?

IMHO put two on. If they are too good next haul out you could reduce the number if you wish.

b-rad 29-10-2009 19:36

I had pre installed it about 2 inchs forward of the strut. Will just latch it down there tomorrow before the big splash.
The shaft had no zincs on it when it came out.
The shaft now is new and nice and shiney but ill scothc brite it just for grins, Im nervous about going back in the water, at least on land it cant sink.

LtBrett 29-10-2009 22:01

Lots of folks put a zinc on the shaft inside of the hull as well, not to guard against corrosion, but to act as a last chance stopper should the shaft start backing out.


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