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Old 12-05-2011, 06:08   #46
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Re: What do you Zinc?

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Originally Posted by GordMay View Post
You don’t appear to understand how sacrificial anodes work, and you're absolutely wrong.

The amount of protection a zinc anode provides depends on its surface area. It takes a zinc with about 1% the surface area of the metal it’s protecting.
The longevity of a sacrificial zinc anode is a function of its weight and composition.

As an anode is “consumed”, it loses both mass and surface area, reducing it’s electrical effectiveness.

Sacrificial Anodes: Aluminium Sacrificial Anodes,Zinc Sacrificial Anodes,Magnesium Sacrificial Anodes,Bracelet anodes,Cathodic Protection Systems

Anode - Calculation

http://www.performancemetals.com/ima...m%20Anodes.pdf
I'm with you on this one Gord. This is one of the least understood parts of boating and I've yet to meet anyone who knows for sure a lot of the issues that come up with properly protecting a boat...me included.

What I do know is the way to test to see if there is enough zinc on a piece of metal is to use a multi-meter and a Silver-Silver Chloride electrode. I bought one at WM years ago and test not only my boats but many others as well. This is the science to the arguement whether or not a piece of metal is protected...but how the boat is zinced and wired and futher protected in all situations is still black majic.


When your system works...that's great right up to the point where something changes...then it gets expensive. The only sure fire method is constant vigilance
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Old 12-05-2011, 06:46   #47
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Re: What Do You Zinc ?

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Originally Posted by aboutgone View Post
And zinc's do nothing on the shaft in the engine room!!!!!
This is absolutely NOT the case!!!

In the photo I posted, you can see that the doughnut zinc is nestled up against the SS rotor on my PSS shaft seal, (with a very thin bead of caulk on their faces).

The SS rotor had previously slid up the shaft, because the rotor's set screws had become rounded. This let about a foot of water into the boat, and if we had not been a trimaran, it would've sunk!

After replacing the rotor, I put on the interior zinc as a "back up", to make sure the SS rotor can NOT move again. THIS Zinc has NOTHING to do with the prevention of galvanic corrosion, And I suggest that anyone with a PSS dripless shaft seal, install the backup zinc in this location. It's cheap insurance!

FOR CORROSION PREVENTION:

In the photo, you can see the "shaft brush". This electrically connects the top, "interior" part of the bronze strut, to the shaft, with a section of wire. (Connecting the wire to the engine itself is unreliable, due to "hit & miss" continuity, created by greased transmission bearings). With the Strut now connected to the shaft "electrically", the shaft zinc that is just forward of the prop, protects the prop, shaft, AND strut!

Mark
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Old 12-05-2011, 14:58   #48
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Re: What Do You Zinc ?

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Originally Posted by Mark Johnson View Post
This is absolutely NOT the case!!!

In the photo I posted, you can see that the doughnut zinc is nestled up against the SS rotor on my PSS shaft seal, (with a very thin bead of caulk on their faces).

The SS rotor had previously slid up the shaft, because the rotor's set screws had become rounded. This let about a foot of water into the boat, and if we had not been a trimaran, it would've sunk!

After replacing the rotor, I put on the interior zinc as a "back up", to make sure the SS rotor can NOT move again. THIS Zinc has NOTHING to do with the prevention of galvanic corrosion, And I suggest that anyone with a PSS dripless shaft seal, install the backup zinc in this location. It's cheap insurance!

FOR CORROSION PREVENTION:

In the photo, you can see the "shaft brush". This electrically connects the top, "interior" part of the bronze strut, to the shaft, with a section of wire. (Connecting the wire to the engine itself is unreliable, due to "hit & miss" continuity, created by greased transmission bearings). With the Strut now connected to the shaft "electrically", the shaft zinc that is just forward of the prop, protects the prop, shaft, AND strut!

Mark
good idea on the zinc...tough to keep those PSS set screws in place.
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Old 12-05-2011, 15:25   #49
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Re: What Do You Zinc ?

Psneeld,

In my case, the set screw had not actually backed up, as I had another one behind it in the hole to "lock it".

My mistake was this... I had occasionally used the rotor to "hand turn" the shaft when cleaning up the engine compartment, including the salt crust on the carbon face. WRONG!!!

The shaft is Aquamet 22, which is a VERY hard alloy of SS! It is so much harder than the SS grub screws, that rather than dimple the shaft when I tighten the screws, it was just slightly crushing the end of the screw. NOT very secure, but probably good enough if I hadn't hand turned the shaft with the SS rotor. (There was VERY little force involved here).

The Zinc is VERY secure and really solves the problem nicely. I now turn the shaft by the much more secure Zinc.

Learning what I did about the insecurity of the little set screws, I have also replaced them elsewhere, where they really matter, with tapped threads and a #10 or 1/4" machine screw... (Stanton bases, bimini top frames, etc.)

Mark
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