Zincs

[les harrison]

Wanted to add an extra zinc as first time we pulled boat prop one was completly gone,anyone know where and how to place one.

 

[Don S/V ILLusion]

To protect the expensive underwater metal stuff, you want to make sure you have at least one good zinc down there. This typically involves one or two zinc collars on the prop shaft. Depending on what prop you have, some also require one on the prop hub to ensure it is protected.

"Where and how to place one" should be apparent once you figure out the shaft diameter and buy a replacement. Screw it together tightly, bang with a hammer and screw again. Location anywhere on the shaft is okay as long as you don't block water flow through the strut bearing.

 

[kloudie1]

Kinda like this, Les.. Try to stay close to the strut with the weight (away from the middle of the shaft) so ya don't create excess vibes. (by shifting the shaft first critical speed to a lower frequency.)

 

[stephen Penny]

Please note 3 zincs - 2 on shaft and 1 on the shaft support. This can be done in the water but may be difficult to "hammer" it closed unless the diver is really good.

 

[JustDucky]

I have been told by our yard manager, when placing multiple zincs on the shaft, be sure they are touching eachother.

 

[Don S/V ILLusion]

I have been told by our yard manager, when placing multiple zincs on the shaft, be sure they are touching eachother.

That's a new one!

 

[zeehag]

funny--my divers never hammer mine closed. lol-- they screw closed. no hammer needed. i have mine done in the water...why are folks so in a hurry to hammer on their prop shaft??

 

[les harrison]

What about adding additional zincs to the one on the prop shaft,my old boat had one you pulled out and left hanging in water when you were in the marina. If I remember correctly it was attached to cockpit drain valves

 

[Dan Johnson]

"Fish" zinc...

When in the boat business, the hanging zinc in the molding of a fish on a line was a common addition we made to powerboats when adding a galvanic isolator. It was used to supplement the meager zincs that were attached to the outdrives. It's a much bigger lump of metal than clamp-on shaft zincs.

 

[jtm]

while I can't figure the importance of making sure the 2 zincs touch eachother, I have kept them close to the strut to hopefully minimize vibes and I also rotate by 90degrees the position of the zinc seam- figuring that I might further average any vibes from being in tandem. Don't know if its true, but I haven't thrown a zinc yet. And I surely won't hammer them- the "football" zincs have a small pimple on the shaft side to ensure contact and to help it bend on tightening the screws/nuts

 

[Rich Stidger]

For the last few years the instructions with the CM (Canadian Metals) brand of zincs claimed that hammering wasn't required anymore. Just tighten the screws.

Years ago, the instructions did say to tap in order to seat the copper ball on the inside of the zinc to ensure good contact. But the new zincs claim that they are machined to a tighter fit and no tapping is required.

I have heard or read that the shaft zinc should be placed close to the strut so that the strut is protected by proximity. Since the cutlass bearing is rubber with no conductivity, maybe there is some truth to this advice.

 

[Rick486]

For the last few years the instructions with the CM (Canadian Metals) brand of zincs claimed that hammering wasn't required anymore. Just tighten the screws.

Years ago, the instructions did say to tap in order to seat the copper ball on the inside of the zinc to ensure good contact. But the new zincs claim that they are machined to a tighter fit and no tapping is required.

I have heard or read that the shaft zinc should be placed close to the strut so that the strut is protected by proximity. Since the cutlass bearing is rubber with no conductivity, maybe there is some truth to this advice.

There is of course the need for water to flow into the cutlass bearing and if the zincs are too close to the strut, that flow may be obstructed.

 

[Rich Stidger]

Well I don't really know how close is too close but checking my pictures from the last ten years I have placed my zinc as far as 6" away and as close as 1" away from the strut. My cutlass bearing lasted eleven years.

My "guess" is that as long as the zinc is not right up against the bearing so that growth could clog the entrance to the bearing it should be OK. There is no mechanism for pumping water into the bearing, I think it simply must be wet. I can't imagine that cooling would be an issue with the entire shaft, bearing and strut immersed in 80 degree or colder water. It's not the same as the shaft log bearing that is dry except for the water drips for lubrication and cooling.

IMHO I don't think placement of the zinc very close to the strut is any real issue of concern.

Anyone have info that shows I'm wrong? Please tell me.....

 

[Dan Johnson]

Rich...

the only thing I can think of that would support placing a zinc close to the strut is an imbalance caused by its erosion that could set up a harmonic in the shaft if placed somewhere in the middle of the space between the shaft's exit point on the hull and the strut. Just a thought...

 

[Dubo]

Strut protection via engine bonding

A fresh zinc thread...just what I needed! Does anyone know if you can successfully protect the strut by bonding it to the engine which in turn get its protection from the prop shaft's zinc? My engine has no zincs by design so I was wondering if the zinc on the shaft would provide what the strut would need via bonding. My second choice would be to tap into the strut and attach a zinc physically to it but that invoilve a haul out.

Thanks for any incite.

 

[kloudie1]

Dubo, I did an electrolysis survey using a reference cell per Nygel Calder's articles. I found that the strut either needed a zinc as you say, or it could be bonded to the engine block provided there is electrical continuity between shaft and engine. Some folks have a "soft" coupling and there is no electrical connection between engine and prop shaft. My strut was not factory bonded to engine.. I did that and re-surveyed. Results showed that my strut is being protected by the prop shaft zincs. Much easier to change a shaft zinc in the water instead of a "bolted on" strut zinc.

 

[Dubo]

kloudie1,
Thank you for the confirmation of strut bonding. I will have to seek out Nygel's article.

Happy sailing!