Making zincs

Don S/V ILLusion · Jun 19, 2009

MoonSailer said:
In short if you are using the right anode material for the conditions you can not overprotect. But if you use the wrong anode material you can overprotect. Magnesium in saltwater is overprotection. Zinc in freshwater is under protection. Aluminun alloy offers good protection in both fresh and salt water.

Not quite true - you can "over-protect". I have no idea where BoatUS got this info but as with all generalities, this one too is misleading.

Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed.
The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water.

Aluminum in salt water is essentially useless as it's effective range of influence is inches.

MoonSailer · Jun 19, 2009

Don do you have any references to support your statements???

As I understand it the two metalls generate a voltage difference with one metal losing metal and the other gaining electrons. Different metal combinations generate different voltages. It is like a 12V battery. Hooking up 20 12 volt batteries positive to positive negative to negative gives you 12 volts!!!!! No matter how many batteries you still get 12 volts. More zinc surface means that the zinc lasts longer but the voltage difference is unchanged. You do need X amount of zinc surface to protect X amount of other metals. Don Casey says to start with 1%. If they are electrically bonded with copper wire I don't think that the distance is critical.....though resistence in the wire will reduce the voltage a little. http://www.boatus.com/boattech/casey/23.htm

tsmwebb · Jun 19, 2009

MoonSailer said:
There is a common misconception that you can overprotect your drive by using too many zinc or sacrificial aluminum anodes. This is not true.

I haven't looked at the links, so I'm sorry if I'm off on a tangent, but with wooden boats there is a problem with too much zinc. The wood near the zinc is attacked and gets soft. Maybe this is where the idea of over-zincing entered the boating zeitgeist...

--Tom.

tsmwebb · Jun 19, 2009

Mike Holibar said:
I saw the manufacturing process and observed there are several "secret" ingredients, other than the base metal, that are added during the smelting process.

http://www.boatzincs.com/use_milspec_a18001k.html is sales speak, but does talk a little about the "secret" ingredients (how secret can a mil spec be?) and why they have them.

--Tom

Hermit Scott · Jun 19, 2009

$65 for an anode !?
The PO of my boat bought a witness 35 cat. The engines are rare that came in those and the parts are crazy expensive. He said the zincs for his engine were some rediculous price also.
Instead of smelting, which I hadn't even considered. couldn't you just machine a zinc to fit from a bigger zinc? If I needed penut sized zincs, I would buy a little larger zinc and grind it to shape and then drill and tap it to fit. You could even take the copper ball and spring out and install it on your new zinc.
If you took an afternoon you could make 20 zincs for future use.

txtowman · Jun 19, 2009

The answer is yes. I use polymer clay or modeling clay to make molds for fishing weights and babbitt bearings. I use a coleman gasoline stove, a cast iron pot "small" and a ladle for casting bullets "I do those too" if you are recycling start with a cold pot and add metal slowly, works best with some virgin material in the bottom of the pot. when the metal becomes a liquid, skim the slag off of the top and discard it. then flake some bees wax and carefully put on the surface of the molten metal. then use a ladle to pour. the hard part is getting a good mold that you can reuse. this is just my personal experience and not a suggestion that you try it. the most important things to remember are:
everything is hot and burns!
foriegn material in the pot or mold may cause an explosive boil.
wear protection "full Frontal" apron, gloves, sleeves, face shield.
these should be fire retardant.
starched cotton clothing provides limited fire protection.
don't put water on the hot metal.

tommays · Jun 19, 2009

All the saildrive ones i have seen that bolt onto the gearcase between it and the prop are pretty big and would require a pretty complex mold

And if you have ever seen a saildrive gearcase price ITs NOT were you want to cut corners

Do a google image search on saildrive zinks and look at the missing gear cases

Hermit Scott · Jun 19, 2009

I think the idea is that a zinc can get corrosion in between the zinc and the prop and then becomes non effective. So the copper which doesn't corrode as easily will maintain electrical contact because it is somehow burried in the zinc. They say that the best zincs have these. In my some what ignorant opinion, I believe if you seat a zinc properly the copper ball is irelevant.
sail361-post a pic of your zinc or a link to a site that has it for sale. Maybe we will have some better ideas as how to get around the rediculous priceing of your needed zincs.

tommays · Jun 19, 2009

saved 65 bucks there goes a 5 k gear case

Rich Stidger · Jun 21, 2009

My solution for outrageously priced zincs......

Ed, I share your pain with specialty zincs that carry big prices. I have a AutoStream feathering prop that uses a nose-cone type of zinc that was about $38 plus shipping a few years ago. I was disgusted.

I looked into molding my own zincs but I found that zinc is a "heavy metal" and during melting the vapor was classified as somewhat toxic. I decided not to use that approach.

My prop zinc slides onto a protruding shaft and is held on with a locknut.

Here is what I did:

I have a small metal lathe and I machined a piece of stainless that would slip over the existing protruding shaft and had an outside diameter of 3/4". I attached that machined part with the locking nut to the prop. Now I have a 3/4" shaft at the end of my prop that I simply attach a standard oval shaft zinc that I buy for $6.

See the pictures below for the original zinc, the prop with the machined adapter installed and with the $6 standard zinc attached.

I have used this for over four years with excellent results. And over $120 back in my pocket. I've even considered producing these machined adapters as a side business, but haven't as yet.

Can you do something similar? Is there a close fitting zinc that you can machine (maybe a friend has machining capabilities?) to fit?

sailingdog · Jun 21, 2009

Rich—

One issue I possibly see with this is that you're adding yet another metal to the mix. Bronze, stainless steel and zinc don't play nice in close proximity underwater.

Rich Stidger said:
Ed, I share your pain with specialty zincs that carry big prices. I have a AutoStream feathering prop that uses a nose-cone type of zinc that was about $38 plus shipping a few years ago. I was disgusted.

I looked into molding my own zincs but I found that zinc is a "heavy metal" and during melting the vapor was classified as somewhat toxic. I decided not to use that approach.

My prop zinc slides onto a protruding shaft and is held on with a locknut.

Here is what I did:

I have a small metal lathe and I machined a piece of stainless that would slip over the existing protruding shaft and had an outside diameter of 3/4". I attached that machined part with the locking nut to the prop. Now I have a 3/4" shaft at the end of my prop that I simply attach a standard oval shaft zinc that I buy for $6.

See the pictures below for the original zinc, the prop with the machined adapter installed and with the $6 standard zinc attached.

I have used this for over four years with excellent results. And over $120 back in my pocket. I've even considered producing these machined adapters as a side business, but haven't as yet.

Can you do something similar? Is there a close fitting zinc that you can machine (maybe a friend has machining capabilities?) to fit?

Hermit Scott · Jun 21, 2009

It looks like Rich's prop is stainless anyway.

Rich Stidger · Jun 21, 2009

It is. All stainless.

sailingdog · Jun 21, 2009

Yes, but is the piece you made duplex stainless steel alloy? If not, then you've introduced a third metal to the mix, which was previously not there.

Don S/V ILLusion · Jun 21, 2009

sailingdog said:
Yes, but is the piece you made duplex stainless steel alloy? If not, then you've introduced a third metal to the mix, which was previously not there.

it would all be protected by the anode regardless

Hermit Scott · Jun 21, 2009

Rich-is your hunter 40 good in the open ocean? The hull of your boat is sort of shaped like mine. I was wondering how it treated you in bad weather.

Making zincs

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