Anode Protection

[fstbttms]

Originally Posted by Cherp

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.

This is absolutely, 100% incorrect. You can absolutley overzinc a fiberglass boat and I see examples of this all the time. I don't know where you're getting your dope, but it's bad.

[Mark Johnson]

Cherp...

I never suggested the use of any form of grease with zincs. (not at all recommended)

In "another thread" I was mentioning the use of an "electrically conductive" grease, (NOT dielectric), when installing my most important cables, like the battery and lightning grounds. As you point out, "electrically conductive" is the opposite of dielectric, which means electrically NON-conductive.

The electrically "conductive" grease that I use, is both to fill the voids where air and moisture could cause corrosion, AND with the fine copper powder that it is loaded with, it increases conductivity a bit at the cable and battery lug's contact points. It is also very useful on really low amp contact points, like a small dab on LED light bulb contacts... They need the best connection possible.

The stuff is:

Jet-Lube SS-30 Out of Houston Texas. Phone # (713-674-7617)

It is sold in small 1/2 pound jars with an applicator brush. It leaves a nasty stain on clothing, so if it is out where you can brush against the excess, I suggest that you clean the excess with mineral spirits.

I board with our 6' boarding ladder that is folded in half, hinged at the top, and always ready to deploy. When sailing, like the photo, It is held up with a break away plastic hook, as a fuse. If I fell in and can get to the ladder, I could reach up and grab it, the hook would break, and the ladder come down. Good point though!

Yes, Here in NC, it is too cold for me to be getting in the water, even with my thin wet suite. Maybe in 6 weeks... Most marinas have divers that come and scrub boat bottoms periodically. (less so in winter) IF you could time it when the guy was going to be in the water anyway, he might only charge $20 to change the zinc. (He will have a good drysuite).

If none of this works, do the dangle over the side thing that you originally mentioned. It can't hurt, might work, and you are only talking a couple of months while waiting for the water to warm up. If your marina slip is electrically neutral, you should be OK for that length of time.

As mentioned elsewhere, ALL boats should have a Galvanic Isolator, so the green wire doesn't connect you to every boat in the marina!

Best, Mark

[Mark Johnson]

Originally Posted by fstbttms

This is absolutely, 100% incorrect. You can absolutley overzinc a fiberglass boat and I see examples of this all the time. I don't know where you're getting your dope, but it's bad.

Ditto that... M.

[GordMay]

Originally Posted by At sea

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...

Indeed.

[Cherp]

Geez....this gets complex. Do you have to dart about with a volt=meter on your anode and hull? Moast people don't do that. Do they just slap on an anode and hope for the best? How do yu know on a glass boat if you even need an anode on the prop shaft? Maybe you're just attaching trouble.

[Wand]

Originally Posted by Cherp

Geez....this gets complex. Do you have to dart about with a volt=meter on your anode and hull? Moast people don't do that. Do they just slap on an anode and hope for the best? How do yu know on a glass boat if you even need an anode on the prop shaft? Maybe you're just attaching trouble.

You'll have dissimilar metals in the underwater parts of your power plant setup, so there will be galvanic action happening (you are in salt water, no?).

I'd suggest putting just one zinc on the shaft to protect the important bits, then keep and eye on it without worrying too much. But perhaps Fstbttms with his (doubtless superior) knowledge of glass craft and electrolysis can advise better.

And you're right Cherp that most people don't dart about with a voltmeter; the rules of thumb about zincs seem to work okay for most. But the voltmeter helps if you're interested in what's really going on down there.

[Bill S]

If it is posssible to over zinc a glass boat, what is the harm? What will happen to a glass boat with too much zinc?

[GordMay]

Metals are receiving cathodic protection, when their measured potentials are more negative than their natural corrosion potentials, and are generally completely protected from corrosion when their potentials measure .20V (200mV) to .25V (250mV) more negative than the values listed in the Galvanic Series charts.

Lower potentials indicate metal erosion - ADD Zinc.
Higher potentials indicate over-protection - Remove Zinc.

For more information on corrosion testing, check out:

Corrosion Testing (Fluke) ➥ http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

And ➥ http://www.cruisersforum.com/forums/...all-10632.html

And ➥ http://www.cruisersforum.com/forums/...sion-2469.html

➥ http://www.performancemetals.com/ima...ard%202010.pdf

[fstbttms]

Originally Posted by Cherp

How do yu know on a glass boat if you even need an anode on the prop shaft? Maybe you're just attaching trouble.

If you have metal underwater, it needs protecting.

[fstbttms]

Originally Posted by Bill S

If it is posssible to over zinc a glass boat, what is the harm? What will happen to a glass boat with too much zinc?

You will damage the anti fouling paint.

[ColinR]

I found that my shaft zincs were eroding around the fasteners and coming loose prematurely. I now dab a bit of paint on the surface of the zincs in the area of the fasteners, and they seem to stay attached longer.

[Cherp]

The plan now - one zinc on the shaft. Dive on it to check it's behaving each six months. I put her on the hard each year, so can keep an annual inspection that way. I also like the sound of the galvanic isolator, and will talk to my local sparky about one of those. I won't venture into the reading noted by GordMay. It sounds like a PhD in its own right. Fstbttms, have you seen the result of over=zincing glass boats? What does it look like? I read a learned paper which more or less said over zincing was not a problem on glass boats, but obviously it was crap.

[fstbttms]

Originally Posted by Cherp

Fstbttms, have you seen the result of over=zincing glass boats? What does it look like?

Typically you would notice "scortching" around thru-hulls and other metal fittings, where the paint would appear to be burned off the hull in a circular pattern around the fitting.