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Cherp · 22-02-2011, 14:51

Hello. My sailboat has shed the zinc anode from the prop shaft. I have rigged a copper wire onto a zinc anode and put the anode over the side. The inboard end is attached to the prop shaft inside the boat. Is that the right place to put it?

Mark Johnson · 22-02-2011, 15:05

In theory that might work, but in practice not likely. The wire connection at the zinc will probably deteriorate, and it would be better if it was ON the shaft, or... closer than 4 or 5' away. I would change out the zinc or get a diver to do it, within a week or so. It is money well spent. Why gamble? Mark

Hydra · 23-02-2011, 13:13

You could even do it yourself, you just need a dive mask. I did it twice.

On my boat, the anode on the propeller is held with a single screw. Then, it's easy to take a big gulp of air and dive with the anode and the screw in one hand, the wrench in the other.

For the anode on the shaft, it's trickier, since there are 2 halves, 2 screws and 2 nuts. After one unsuccessful attempt (lost one half-anode), I took the precaution to tie a thin safety line to both parts of the anode, held by somebody on deck. This time, I was successful. I just had to dive twice, to fasten the 2 screws.

Alain

Blue Stocking · 23-02-2011, 13:41

For shaft zinc replacement, before getting wet, I remove one screw, and replace it with a zip-tie to hold the 2 pieces together. This will hold the zinc on the shaft while you tighten the other screw. Remove tie, and insert 2nd screw.

Cherp · 23-02-2011, 15:02

Hi....I spoke to a local electrician the other day and he said the "zinc over the side" plan will actually work. He says quite a few wooden boats in this area use it as their only means of electrolysis protection. Nonetheless, I've booked to put her on the hard tomorrow to replace the shaft zinc - but I'll put two on this time. The shaft zincs are a bit problematic. By their nature they will erode, thereby loosening their grip on the shaft. It's a pretty poor setup really. I might try to work out a better plan, although nothing hits me between the eyes just yet. Replacing them underwater from time to time is actually feasible, by means expressed by people on this thread, but a bit desperate. If I have a flash of brilliance I will report it.

**Cotemar** · 23-02-2011, 15:20

Cherp,

If you have room. Put three zinks on the shaft. Make sure to stager them.
They always wear from the outside in, so they should alway remain tight on the shaft.
We used to go 2 years with these 3 zinks as shown in the picture. Once they get to 50% then its time to change them.
I always clean the shaft with 3M scotch bright pads and then put electrical contact grease on the shaft and zink to make a good contact.

Mark

Cherp · 23-02-2011, 17:15

Mark...that looks good. That's what I will do. There is room for three.

Wand · 23-02-2011, 17:37

Quote:

Originally Posted by Cherp

Mark...that looks good. That's what I will do. There is room for three.

Ah, but that raises the hoary old chesnut of whether you can have too much zinc. The steely community endlessly chew the cud on this, but one prominent thought is that you definitely can have too much.

The argument goes that you need to measure the voltage potential between the steel and the zinc and, if it's below or above a defined range, then you need to add or remove some zinc.

From memory, if the reading is too low then more zinc is needed to counter the galvanic action. Or if the reading's too high, tiny hydrogen bubbles will form under the paint and lift it so you should remove some zinc.

I don't know if any of this has relevance to shaft-only zincs on non-steel vessels. But may be worth a little thought.

amarinesurveyor · 23-02-2011, 17:49

A galvanic isolator (zinc saver) will probably solve your problem. Easy to install in the shore power ground, which is where stray DC current can get into your boat and erodes your zincs. It prevents low voltage DC current from entering the boat, but allows current from the boat in the direction towards shore from your boat if it is needed.
I wouldn't put three zincs on; I'm not even sure if two would be too much.
Good luck, Brian

Mark Johnson · 23-02-2011, 17:49

Changing your zinc in the water, With just a mask, fins, and snorkel, is a piece of cake, (if the water isn't too cold). I've done it hundreds of times. In the sailing season, I wipe off my hulls with a gloved hand to knock off the slime, every time I go out, and buff off the zinc too.

You need the zinc, a hex key, scotchbrite, and a very small hammer, or something to tap with.

First breath, you go down and scotchbrite the shiny spot on the shaft for good contact. Next breath you go down and put the two haves together over the shaft with the slit vertical, and the screws horizontal, and press FIRMLY. (30 sec max) If it feels stable, it will hang there. Catch your breath... On the third dive, take the hex key and loosely snug the screws. Come up for air... fourth time, snug really snug, but be sure that one side is not closer to touching than the other. One last trip down, and tap both halves together with a hammer, screwdriver handle, whatever. (just a few good taps), Then snug with the hex key one more time.

The triple zinc idea does give a safety in theory, but not unless it slings one. This should not happen if you put it on right, like I described. Also, I suggest that you always change it when it is about half way gone, LONG before it is likely to fall off. This way the electrical contact can be counted on.

Multiple zincs do not protect any better, but might last longer... at a price. It makes the prop less efficient, and if the prop is not painted, the additional current that it creates, will attract barnacles to the prop more. The dissimilar metals, in salt water, create a battery, and the more current, the happier the critters are.

One other thought, especially during warm enough weather to be diving on the boat, You should dive over and gently scrape the scale, slime, cement like coating off of the zinc, with the blade of a small putty knife. The contact with water keeps them working, and frequent diving to look, gives you peace of mind that all is well.

Hope this helps, Mark... (another one)

Cherp · 23-02-2011, 17:51

At Sea...I went into this a bit. The too-much/not enough zinc calibration is important on steel and aluminium boats, but not glass ones. Apparently if you have too much zinc on a steel/aluminium it will start spitting off paint. There's another question for Mark - I looked up dielectric grease, and discovered that it is non-conductive. Would that not prevent the anodes from working? If it is non-conductive and lasts a long time in water, it must surely prevent the progression of the zinc atoms along their path, which is what prevents the corrosion of the parts you are trying to protect in the first place? Maybe no grease, or a bit of vaseline? Not sure if vaseline is a conductor either. Maybe nothing.

Cherp · 23-02-2011, 17:56

Mark Johnson...how do you get back on Delphys from way down there?

Cherp · 23-02-2011, 17:57

Current thinking is two zincs, no grease and a bit more spine to jump in once every few months with the appropriate tools. Mind you, the water is cold in my part of the world.