Zincs on aluminum hulls

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Ferg2721
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Zincs on aluminum hulls

#1

Post by Ferg2721 » Mon Feb 27, 2017 3:01 pm

Hello there! New member here with a question about zincs. Outboard motors always have zincs in electrical contact with the aluminum components. So it seems odd to me that my aluminum boat didn't come with zinc anodes either on the outside or inside of the hull. Is there a reason for this? Should I consider installing one or more? If so, what should the fasteners be made of? Thanks in advance.

kmorin
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Re: Zincs on aluminum hulls

#2

Post by kmorin » Mon Feb 27, 2017 4:18 pm

Ferg2721, welcome to the AAB.com Forum.

outboard engines generate current by all sorts of means. That charge or voltage potential is dissipated/conducted to the water at the zinc. Hulls don't all have power systems so hey don't have charges on/in them. When you install a power system other than an engine on a metal boat you should provide stray current protection by installing sacrificial anodes.

In a riveted skiff like a Lund, Star-craft, Gregor or equivalent- unless there is a battery and some other electrical gear installed (?) there's no source of a charge in that hull to need sacrificial anodes. If you add an battery system to an originally 'bare' boat; you should add anodes of the correct alloy (not all are zinc) and size for the boat and the amount of power you're protecting the boat from.

Mounting an anode can be done with bolts the main focus is the metal of the mount and the anode be in close contact without insulation. Many boaters rely on SS to mount their anodes. Galvanized bolts work fine if the threads are coated too- some of these fasteners come with bare steel threads and are a problem underwater in contact with any aluminum part.

Depending on the hull material and design of the boat some anodes come with weld-on tabs. These are usually the ends of a flat bar of aluminum that has been cast into the anode material protruding at the ends. These bar ends are held flat to the hull material and welded directly the plate hulls providing both a good electrical connection and a strong mechanical connection. This type of connection is usually used on larger welded boats.

Cheers,
Kevin Morin
Kenai, AK
kmorin

Ferg2721
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Re: Zincs on aluminum hulls

#3

Post by Ferg2721 » Mon Feb 27, 2017 6:04 pm

Thanks for the prompt response! As it turns out, I do have a solar panel and regulator that keeps the battery charged. Sounds like it would be a good idea to add some protection with stainless steel bolts on a patch of bare aluminum.

kmorin
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Re: Zincs on aluminum hulls

#4

Post by kmorin » Mon Feb 27, 2017 7:14 pm

Ferg2721, its considered best practice to weld on a spare tab or bracket of aluminum so the bolts don't have to penetrate the hull in any way in order to mount the anode(s).

Cheers,
Kevin Morin
Kenai, AK
kmorin

Chaps
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Re: Zincs on aluminum hulls

#5

Post by Chaps » Mon Feb 27, 2017 9:36 pm

Depending on the boat and how much time it spends in the water you may find that the anode on the engine is sufficient to protect the entire boat though it's always a good idea for the hull to have a dedicated anode particularly if it's used in saltwater as the engine anodes are really only engineered to protect the engine. BTW aluminum boats are better protected utilizing aluminum anodes that are alloyed to be slightly more active (sacrificial) than zinc anodes. Your engine would typically already be equipped with an aluminum anode if it was sourced from a dealer that sells your brand of engine. As far as install you would be served by posting up a picture of the transom on your boat to get some input on appropriate anode attachment possibilities. You may have a flange or tab that is always underwater thus enabling a conventional bolt-on anode. Weld-on anodes are very good but changing them is a pain unless you have ready access to a shop that welds aluminum.
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Ferg2721
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Re: Zincs on aluminum hulls

#6

Post by Ferg2721 » Wed Mar 01, 2017 9:33 am

Thanks, Chaps! There is a nice little 1 inch extension of the hull planning surface at the transom that would make for a mounting location that doesn't pierce the hull.

What are your thoughts regarding zincs in the bilge? I keep the boat on a trailer with bow up and the drain plug out, but salt water is in there for up to a week or so on longer trips.

pjay9
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Re: Zincs on aluminum hulls

#7

Post by pjay9 » Wed Mar 01, 2017 2:03 pm

I did not know that there were ALUMINUM anodes. Interesting.
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Chaps
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Re: Zincs on aluminum hulls

#8

Post by Chaps » Wed Mar 01, 2017 4:35 pm

Ferg2721 wrote:
Wed Mar 01, 2017 9:33 am
Thanks, Chaps! There is a nice little 1 inch extension of the hull planning surface at the transom that would make for a mounting location that doesn't pierce the hull.

What are your thoughts regarding zincs in the bilge? I keep the boat on a trailer with bow up and the drain plug out, but salt water is in there for up to a week or so on longer trips.
This mercury outboard anode could be bolted to your flange using two of the holes along an edge, it would stick out a bit but would provide needed protection. I wouldn't worry about installing anodes in the bilge.

http://www.boatzincs.com/MER818298A.html

Yup Capt PJ, aluminum anodes for aluminum boats is the way to go. Can't tell you how many zinc anodes I remove from aluminum boats that show no sign of activity yet the hulls they are supposed to be protecting show pitting and paint failure.
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