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jerlim
Master Marine Consultant

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USA
1484 Posts
Initially Posted - 03/05/2007 :  19:01:51  Show Profile
I've read through the posts about where to install them on a swing keel, and how to drill and tap holes. I'm wondering about the wisdom of drilling holes into the keel, doesn't that just give rust a place to get deeper into the casting?

Does anyone simply epoxy zincs onto the keel?

Thanks!
Jerry
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Leon Sisson
Master Marine Consultant

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USA
1893 Posts
Response Posted - 03/05/2007 :  19:50:14  Show Profile  Visit Leon Sisson's Homepage
Gluing zincs on defeats the whole purpose. There must be a <b>*very*</b> good electrical connection between the sacrificial anode and the metal part being protected from corrosion.

As for "<i>...drilling holes into the keel, doesn't that just give rust a place to get deeper into the casting?</i>" I understand your concern. I use a narrow ring of sealant around the hole in the keel (but out a bit from the hole) before attaching the zinc. Obviously it's important to not use so much sealant so close to the hole that it interferes with the contact between the zinc, bolt, and keel. (My keel is fiberglass encapsulated, so there wasn't going to be any electrical contact beyond the bolt anyway.) I've been doing this for several haulout cycles in warm saltwater. Each time, the zincs are eaten up, as they should be, and there's no sign of rust in the bolt holes. So far, so good!

-- Leon Sisson
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crcalhoon
Captain

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USA
303 Posts
Response Posted - 03/05/2007 :  20:17:56  Show Profile
There used to be a guy in my marina in New Orleans who hung a zinc over the rail suspended by a wire from a shroud. He removed it to sail, then re-hung it when he came in. It did get eaten up properly- well, the water there was only brackish, so what's proper? But I don't know about the absolute efficacy. I have heard or read that that is common on naval warships, but don't know if that's true either. Still, I don't see what it could hurt.
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Dave Bristle
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Djibouti
10005 Posts
Response Posted - 03/05/2007 :  21:47:51  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by crcalhoon</i>
<br />There used to be a guy in my marina in New Orleans who hung a zinc over the rail suspended by a wire from a shroud.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
It won't hurt, but will only help things that are electrically connected to the zinc. If he has a cast iron keel and has grounded the rig to it, then it'll help the keel--although stainless steel is not a very good conductor, so that approach is not optimal.
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jerlim
Master Marine Consultant

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USA
1484 Posts
Response Posted - 03/06/2007 :  10:49:19  Show Profile
I didn't understand the electrical connection concept. As always MANY THANKS GUYS!!!
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OLarryR
Master Marine Consultant

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USA
3521 Posts
Response Posted - 03/07/2007 :  05:39:39  Show Profile  Visit OLarryR's Homepage
The way the zinc works is thru the flow of electrons, etc and that means that the surfaces/matls be able to conduct electricity. It is not that the zinc is electronically charged or hooked up electronically, it is just the nature of the zinc acting as the matl that corrodes, it is a sacrificial galvanic anode. On warships, etc it is used in some areas (tanks, etc) for cathodic protection. Actually, the difference in electrical potential between two areas causes current to flow from the cathodic to the anodic area through the metal and then from the anodic to the cathodic area through the electrolyte to complete the circuit. Salt water is an electrolyte.

An electricity can also be used to generate cathodic protection but the use of zincs is more the way the metals interact galvanically.
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.