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Old 14-10-2008, 20:14   #1
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Zinc Question

I have a fiberglass boat. Most of the thru hulls are Maerlon (sp?). The boat has a Max Prop. There are a total of 4 Zincs on the boat distributed as follows: 2- 1" Zincs on the prop shaft, 1 - cone Zinc on the prop itself, and 3- a plate Zinc that I need to custom make every time I replace it that is attached to 2 staniless bolts that come out of the hull above the prop shaft. I don't know what they are connected to inside the boat. The zincs on the shaft are fine. The zinc on the prop is fine. The plate Zinc though was almost completely gone. The Zincs are all the same age (6 months). I have been plugged into shore power. Any idea why this might have happened?
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Old 14-10-2008, 23:07   #2
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[quote=Charlie;215737 a plate Zinc that I need to custom make every time I replace it that is attached to 2 staniless bolts that come out of the hull above the prop shaft. I don't know what they are connected to inside the boat. [/quote]



I would be interested in knowing what the plate is attached to.
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Old 14-10-2008, 23:53   #3
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The two bolts are most likely attached to a bonding system inside the boat. If you have all Marelon thruhulls you shouldn't need the plate.

Normally those plates are on powerboats hooked to the transom just below the waterline.

BTW Those bolts are a common place for water seepage into the boat. They need to be pulled periodically and resealed.
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Old 15-10-2008, 07:48   #4
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Thanks for the info Del. I will see about rebedding those next time I haul. I never would have thought of it otherwise. I don't know what part of the bonding system they are hooked to. I'll investigate some day when I have more time. It will be interesting to see. Can't figure why that Zinc would be so bad and the others to have almost no disinigration at all.
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Old 15-10-2008, 10:38   #5
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IF the plate is connected to a bonding system and the prop shaft is NOT bonded and you have stray current issues.... the dissolving plate would make sense.

But... before you just rip it off, you might be sure you understand how the whole system is connected and works. That big plate MIGHT be protecting the zincs on your shaft..
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Old 15-10-2008, 10:54   #6
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Quote:
Originally Posted by GreatKetch View Post

But... before you just rip it off, you might be sure you understand how the whole system is connected and works. That big plate MIGHT be protecting the zincs on your shaft..
Do you know of a good resource that explains the whole Zinc process in detail? I have a few books, but they seem to all just glaze over it, and I am looking for a serious in depth source that I can really learn from. Any thoughts would be great.
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Old 15-10-2008, 13:24   #7
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IF the plate is connected to a bonding system and the prop shaft is NOT bonded and you have stray current issues.... the dissolving plate would make sense.

But... before you just rip it off, you might be sure you understand how the whole system is connected and works. That big plate MIGHT be protecting the zincs on your shaft..
I wasn't going to ripit off but I just find it strange that at this Marina I should find the plate Zinc deteriorating badly and at the other Marina it was the prop zincs. I wonder if I should attach a wire and Zinc to the bonding circuit and another to the shaft and hang them over the side. Pretty strange stuff this stray electrical current.
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Old 15-10-2008, 13:38   #8
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Quote:
The two bolts are most likely attached to a bonding system inside the boat. If you have all Marelon thruhulls you shouldn't need the plate.
I have a large plate zinc and Marlon through hulls. The Zinc was an origianl and was replaced for the first time by me last fall. As noted it was part of the bonding system but I also had a bonding plate right next to it. You may want to look at Camp Zincs. They make a large plate zinc with slots on it and can fit multiple types of bolt spacings. Mine was an original Vetus bar that was pretty expensive.

If you eat one of those in 6 months I would say there is some stray voltage going around. Might be as far as five or six boats away. Eating that much zinc needs help. It could be your own boat too.
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Old 15-10-2008, 13:54   #9
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I agree there must be stray voltage but am leaving that Marina. The last plate Zinc that I had lasted 18 months and still had 50% left to it. One of those Isolation Transformers look pretty good to me right now If I only had a few thousand bucks to waste/spend. My logic is that it is the Marina since the last one lasted so long and I haven't made changes to the bonding. I'll see how it works at the next Marina.
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