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sailorchic34 21-07-2012 15:56

The Blonde Zinc Replacement
So here I was floating in the California delta, and I decided to check my prop zinc. I have one of those cone zincs that go on the end of the prop shaft.

So I dove and looked / felt and what do you know, No zinc. To make matters worst no screw that holds the zinc on either.

Now I hate not being able to do all the boat chores, and paying a diver to change the zinc is, well, I'd rather find a way to do it myself. After a few dives I learned that this girl does not work well underwater, that whole lack of air thingy really gets to me.

So being an engineer and blonde, I started thinking out of the box again. So not a good thing sometimes.

On my boat I have a really large sea strainer. Well Large for my dinky little diesel. Something like 1-1/2” size which is 4” in diameter and 12” high in brass and glass construction. Its connected to the seacock with a 2” diameter copper standpipe, which places the top close the the water line.

So I take the cover off, and pull the basket out. Wow, the Size C prop cone zinc easily fits within the basket strainer and leaves room all around. Nice So I drilled out the zinc shaft hole to match the 1/4” copper rod the holds the cover of the strainer down. I slid the zinc inside the basket, and its a really tight friction fit on the brass rod. Cool.

Then I got some #12 wire out and a few terminal ends to fit the " rod. I attach the wire to the rod between the cap and wing nut and attach the other end to the aft engine mount. Just to make sure, I measure continuity between the prop shaft and wire at the engine mount and at the copper standpipe. Neet... zero ohms. We have continuity..Life is good.

Oh I'll probably upsize the wire to the strainer, but it will be a week or so before I hit a dock / location where I can get some.

As we all know, its rather important that the zinc be electrically connected to the prop shaft. Normally the zinc is mechanically connected on the prop shaft, but that's way too messy for this girl anyway.. Plus the cone zincs have a nasty habit of falling off, when the mount hole gets bigger from zinc loss. So annoying.

I'm thinking that based on the engineering text I read that the blonde zinc replacement might just work fine. The zinc is located inside the basket strainer so any little bits of zinc that break off will be trapped in the basket

So now I have an easy way, in theory anyway to check and replace my prop zinc without getting wet. I'm going to check it over the next few weeks to make sure its hum sacrificing itself.

Now I know there will be a few guys here who will say this will not work. Its Cruisers Forum after all. But I'm just going to give it a try and see what happens. The engineer in me says this will work and the blonde says hey, hair and makeup are good to go. Sort of a blonde win win...

Jd1 21-07-2012 16:16

Re: The Blonde Zinc Replacement
Color me confused ....
Sure you got a zinc floating in salt water but are you thinking that you have perfect connectivity from the zinc to the engine out the driveshaft (through a coupler) and into the prop ? What about the path through the water back to the zinc ?

I think there is more blondness than engineering in that solution ....

Therapy 21-07-2012 16:26

Re: The Blonde Zinc Replacement
That sound OK I guess but somewhere I read that the zinc has to be in close proximity to the prop itself. Physical proximity. Not just electrically by ohm meter. I don't know where I read it though.

Good luck. I hope the test does not cost you a prop.

fstbttms 21-07-2012 16:38

Re: The Blonde Zinc Replacement
Jeezus- all to save the cost of a diver for 15 minutes? :rolleyes:

BTW- the longer the electrical path between the anode and the item (theoretically) being protected, the less protection is provided. And that's assuming (as previously mentioned) that you have good electrical contact between the zinc, shaft & prop. Reinventing the wheel rarely results in a better (or even adequate) solution.

barnakiel 21-07-2012 17:14

Re: The Blonde Zinc Replacement
On our ship there is no anode on the prop. There is one on the shaft. This one can be replaced without lifting the boat but it is easier in a calm anchorage on a calm day.

Maybe there is some space on your prop shaft where you could place an anode too?

Just guessing.


sailorchic34 21-07-2012 17:45

Re: The Blonde Zinc Replacement
My shaft extends all of 1/4" from the hull to the back of the prop. So no room for a shaft zinc. There's barely enough space behind the prop to get the zinc on between it and the rudder. It's a very tight aperture prop opening.

My basis is anodes for underground pipelines. Where there is wire bonded from the anode to the pipe protecting hundred's or thousands of feet of pipe line My shaft is all of 48" long. The wire from the rear transmission mount to the sea strainer is less then 24".

BTW The zinc in the sea strainer is less then 24" physically from the prop.

Measured ohms from the front of the shaft ( I have a Vdrive) to the sea strainer is 0.00 ohms. Based on the science it should work.

As far as the diver goes. We'll I'm not at a dock, but on the hook. So its a bit more then 15 minutes for a diver to get to me. I'll be at a dock probably in a week or so. I plan on checking the zinc over the next two weeks. If it works I'll keep it. If there is no measureable loss on the zinc, Then I'll get a diver to replace it. Just no diver around where I'm at....

fstbttms 21-07-2012 17:51

Re: The Blonde Zinc Replacement
How long do you plan to keep the boat in the Delta? Something else to consider- zinc anodes are not really suitable for freshwater or brackish environments. Zero depletion in two weeks may merely mean that your anode should be aluminum or magnesium, not zinc.

sabray 21-07-2012 17:57

Not sure what the screw is that's missing. I'm a guy so need pictures. Usually it's a collar that gets around the shaft. Then their are zincs that thread onto the shaft on threads that are also. Holding the prop in place. Are you saying there is no thread left to attach a cone. Is something eating up the zinc stray current etc... Replacing the zinc is good but what is going in that caused the failure. Don't degenerate yourself by playing girl and put down men by categorically thinking we can't be helpful. Your bright with your solution.why the proper install failed is something to look at.

fstbttms 21-07-2012 18:05

Re: The Blonde Zinc Replacement

Originally Posted by sabray (Post 995725)
Not sure what the screw is that's missing. I'm a guy so need pictures.


Originally Posted by sabray (Post 995725)
why the proper install failed is something to look at.

What makes you think there was a failure? Anodes are supposed to deplete and go away. That's how they work.

sabray 21-07-2012 18:12

Cause usually there is something left of the anode.To loose the whole kit suggests something isn't right. Bad install or stray current. Come on man you know this.

fstbttms 21-07-2012 18:15

Re: The Blonde Zinc Replacement

Originally Posted by sabray (Post 995735)
To loose the whole kit suggests something isn't right.

No it doesn't. It means that the zinc depleted to the point that the screw wasn't under tension anymore and backed out.

sailorchic34 21-07-2012 18:17

Re: The Blonde Zinc Replacement
Well I am sitting in fresh water, so Magnesium would be better, though all I have is zinc. Zinc will work, better then aluminum though not quite as good as magnesium.

Though I do move around a bit and make it back to the central bay too now and then.

Well It has been about a year since the last zinc replacement. The problem with the cone type zincs that mount to the end of the prop shaft is they tend to loosen around the single screw that holds them in. Then they fall off usually while moving.

Plus I'm missing the screw that attaches it, which is the second time that has happened too.

I don't expect much resistance loss in the 1.125 shaft and I measure ohms from the center of the shaft to the sea-strainer and copper standpipe. I do think a thicker wire will help too as we're dealing with millivolts here and the ohm losses involved can't really be measured with the cheap VO meter that I have. Probably will upsize to #4 or larger wire size.

I just know that my ohm reading is as good as I can get it at this time. Figure its better then no zinc at all anyway... which is my other option at the moment...

fstbttms 21-07-2012 18:20

Re: The Blonde Zinc Replacement

Originally Posted by sailorchic34 (Post 995737)
Zinc will work, better then aluminum...

No it won't.

sabray 21-07-2012 18:29


Originally Posted by fstbttms
No it doesn't. It means that the zinc depleted to the point that the screw wasn't under tension anymore and backed out.

I disagree unless the boat is not maintained. If the zinc depletes it should have no effect as the screws are not tensioned by zinc.Collar zincs have a sleeve that has the load. Not sure how cone zincs work but think they also have a load sleeve. Either way best to get the zinc back in its proper place. We agree on that yes.

sailorchic34 21-07-2012 18:35

Re: The Blonde Zinc Replacement
HUM. on the galvanic chart, aluminum is more noble (Ie lower voltage potential) then zinc, IE less current inductance, so zinc protects aluminum. Or more exact the induced current is lower in aluminum then in zinc. See chart below

I'm not sure how a aluminum anode would protect a bronze prop from zinc in the bronze leaching due to micro galvanic action. The galvanic potential does not seem to work between the two...

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