Sense or Nonsense Hanging Zinc Anode Overboard?

[Goudurix]

Hum

I guess it is the system (anode + cathode) that gets more negative with regard to the reference cell as per net "the system" sheds off postive Zn++ ions at a faster rate than the cathode can shed electrons to form OH-
?

Jan

[sailorchic34]

Originally Posted by Goudurix

Hi Sailorchic34,
I see you're in SF Bay I guess cold water even in summer however it just takes a 3mm wetsuit, a diving mask and fins to have a quick look underwater. The visual inspection is the best inspection and at a fraction of the cost of a haulout. Or find a gentleman on the dock willing to do it

Jan

Ah the broke chic can't even afford $20 for a diver, so a wet suit is out the window too. Plus I have enough positive buoyancy problems without a wetsuit.

Actually the prop and hull are fine. The delta water is warm enough to swim in in the summer. Alas,somebody can't hold her breath and attach a prop zinc at the same time either... Thus my fishy zincy thingy was born. No mucking about getting green bottom paint in the hair or dropping screws, etc, either.

[a64pilot]

SC, while I won't to believe in the fishy zincy thingy myself, I wouldn't rely on it solely, props and shafts can add up quick.
PM me a size and shipping address and I'll send you a shaft zinc, don't worry somebody will help me out when I need it too.

[sailorchic34]

Originally Posted by a64pilot

SC, while I won't to believe in the fishy zincy thingy myself, I wouldn't rely on it solely, props and shafts can add up quick.
PM me a size and shipping address and I'll send you a shaft zinc, don't worry somebody will help me out when I need it too.

What a great guy..

Oh I have two or three prop zincs still in the kitty. So the zinc is not the problem. The boat came with about 10 spare zincs and I've yet to buy one. Also, my prop is only about 1/2" from the hull, so shaft zinc's will not fit on Islander 34's.

I'm limited to a prop zinc only and that only just fits. It's a tight aperture prop. Which is what makes it so much fun to try to put on a zinc while holding ones breath and

I actually have high confidence that the fishy zincy thingy works fine. It's practically the same arrangement shown in the fluke writeup eariler, except rather then a zinc attached to the hull, its on a wire. The principle is the same though.

A prop/ sfaft zinc anode is just one of three ways to protect from galvanic corrosion. There is also the remote zinc, as indicated by fluke and others and as I'm doing now and also impressed current which larger boats/ships use quite a bit.

I may play around with impressed current at some time as the DC source is easy to come by.

[a64pilot]

Impressed current, that's the systems you can buy to protect the boat? Heard a lot about them many years ago, but now that I think about it, I haven't heard anything lately.
Do they work?

[goboatingnow]

Originally Posted by a64pilot

Impressed current, that's the systems you can buy to protect the boat? Heard a lot about them many years ago, but now that I think about it, I haven't heard anything lately.
Do they work?

Tends to be only cost effective for large steel boats and impractical on smaller boats with unsure power supplies. It in essence duplicates the activity of a zinc galvanic cell.


dave

[sailorchic34]

Originally Posted by goboatingnow

Tends to be only cost effective for large steel boats and impractical on smaller boats with unsure power supplies. It in essence duplicates the activity of a zinc galvanic cell.


dave

Quite correct, With a typical zinc to bronze/SS your getting about 250-300 mV between the zinc and bronze due to their natural galvanic values.

With impressed current you still have an anode, but it's not galvanic negitive to the other metals its protecting. A positive impressed current at +12V's DC is run through the anode(s) based on the amount of metal to protect.

Based on one design manual I read, you want ~50 mA per square meter of surface area being protected. For a typical non metal sailboat with solar the load works out to ~ 3 watts. The reason its not made for small boats is its too simple and not enough money in it.

OK, it's a bit more complicated then that from a calculation standpoint, but for a small sailboat <50 feet, there's just not much metal exposed.

Basically you run a wire from the + side of the battery to a metal anode in contact with the water adjacent to the metal being protected. Could be SS, cast iron, really anything. Seawater has a 40 ohm resistance according to the manual I read here Designing Cathodic Protection Systems for Marine Structures and Vehicles - Google Books


As the minus side is most likely already connected to the engine and prop shaft, that's about all there is to it. You could get fancy and add a shunt and DC mA meter and of course a fuse in the circuit would be required . But for the basic sailboat that's it.

3 watts with solar panels is not a problem. I will be playing with this a bit I'm thinking.