Prop zinc missing!

[selkirksghost]

Underway for a month. Replaced the prop zinc before leaving. Dove on the hull at the other end to find the prop zinc gone. Don't remember a big thunk of it getting thrown. It was a CMP "D", and the retaining Allen screw was still in place.
???

[sammyo]

Check to see if there is some serious current electrolysis that dissolved it.

[sammyo]

Or nasty evil ninja divers stealing boat zincs in your area...

[JPA Cate]

If the zinc goes away where the screw is, then the rest of the zinc just falls off. Have once or twice lost them that way.

Those are very expensive zincs, shame it's gone; hope you're somewhere you can get another. It might be interesting to have a chat with the manufacturer, though.

Ann

[weavis]

Originally Posted by Ann T. Cate

If the zinc goes away where the screw is, then the rest of the zinc just falls off. Have once or twice lost them that way.

Those are very expensive zincs, shame it's gone; hope you're somewhere you can get another. It might be interesting to have a chat with the manufacturer, though.

Ann

Yes. I have experienced this but not in a month though.
Better check your electrics as some serious action would appear to be going on, especially as you say you were on the move.

[model 10]

Perhaps you over tightened the Allen screw and cracked the zink? I don't think the odds are so good for hearing the parts hit the hull.

[sailorchic34]

A little trick is to paint a dab of nail polish or paint of choice, on the recessed hole where the screw bears on the zinc. The inside contact area remains unpainted so the zinc is still in circuit. The nail polish/paint stops the electrolysis around the attachment screw head and lets the zinc last longer, while still being effective.

[Jim Cate]

Originally Posted by sailorchic34

A little trick is to paint a dab of nail polish or paint of choice, on the recessed hole where the screw bears on the zinc. The inside contact area remains unpainted so the zinc is still in circuit. The nail polish/paint stops the electrolysis around the attachment screw head and lets the zinc last longer, while still being effective.

Interesting idea, SC. I suppose that using a nylon washer under the bolt head would do if one was short on nail polish.

Actually, we keep a bottle of nail polish around for lots of small marking jobs. Good for marking halyards at reef points and such. Never thought of using it as electric isolation material... good one!

Jim

[MeLindaB]

The Ashley river in Charleston eats zincs super fast

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[selkirksghost]

Originally Posted by Guy

Perhaps you over tightened the Allen screw and cracked the zink? I don't think the odds are so good for hearing the parts hit the hull.

Yes, that might be an issue. Did it in the water with a pair of vise grips. (Allen wrench wouldn't fit in the aperture.)
Corrosion seems a bit unlikely, considering we weren't inport very long, and our DC electrical system is rather small. My wife (and myself) left the fingernail polish at home, but I'll keep it in mind. Its hard shell-like finish is handy for many unorthodox uses. The full kit IS advertised with a nylon washer.
But I'm starting the crew on continuous night watches for evil ninja divers.

[markpierce]

Originally Posted by sailorchic34

A little trick is to paint a dab of nail polish or paint of choice, on the recessed hole where the screw bears on the zinc. The inside contact area remains unpainted so the zinc is still in circuit. The nail polish/paint stops the electrolysis around the attachment screw head and lets the zinc last longer, while still being effective.

Brilliant!

[OceanSeaSpray]

Originally Posted by sailorchic34

A little trick is to paint a dab of nail polish or paint of choice, on the recessed hole where the screw bears on the zinc. The inside contact area remains unpainted so the zinc is still in circuit. The nail polish/paint stops the electrolysis around the attachment screw head and lets the zinc last longer, while still being effective.

YES! It is an absolute must do. You can use polyurethane sealant, tallow, lanolin, anything that won't wash off and will keep the water from getting between the stainless fasteners and the zinc.
I normally use a sealant and I put it around the screws etc as I assemble the anode onto the shaft and then fill the recesses around the nuts / heads.

In your case here, it might have fallen off for a mechanical reason, or you have an electrical issue, because one month is way too quick for corrosion around the fasteners only.

[Greg4cocokai]

I've lost a prop zinc once and now tighten the screws often as they seem to get loose from the zinc wearing. I also put 3-4 coats of nail polish outside the screws. They last twice as long!