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Old 20-12-2012, 12:41   #16
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Re: Hanging The Fish Zinc In The Marina Trick

Zinc fish can be useful, but you should also look at your boat's shore-power connection. Adding a diode ground-isolator, or better-yet, an isolation transformer, can greatly reduce your electrolysis issues.

When VALIS was in San Francisco, I was able to keep the batteries charged with my solar panels, so I had no shore-power connection and my Zincs lasted a long time. Since I moved VALIS up to the PNW, I've found I need to run a small heater to keep the condensation from being a problem. This means I need to run shore-power. I installed a diode isolator (this one), and hang a Zinc fish from the backstay chainplate. We shall see how my zincs hold up. I need to make some current measurements -- I don't know if I really need the fish.
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Old 20-12-2012, 19:27   #17
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Re: Hanging The Fish Zinc In The Marina Trick

I try to keep the shorepower unplugged during the daytime when the panels are getting full sun, and anytime we leave the boat for a while. With us onboard at night in the marina we suck down power and I'd rather not cycle the batteries that much.

Here's the one I've seen everywhere:

http://www.defender.com/product.jsp?...9712&id=150598
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Old 21-12-2012, 01:53   #18
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Re: Hanging The Fish Zinc In The Marina Trick

You can make your own. Most boat yards have lots of old zincs lying around.
Some plastic coated SS wire is all that's needed. It is difficult to get a low resistance connection, but if drill a few holes in the zinc thread the wire in and out then use a bolt to squash the bare wire against the zinc or use a prop shaft zinc, but squash the bare wire between the two halves.
Check the resistance of the connection every so often.

It's cheap and green.
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Old 21-12-2012, 08:24   #19
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Re: Hanging The Fish Zinc In The Marina Trick

I fitted an 'over the stern' fish anode 6 months ago, for marina use, at which time the shaft anode was completely intact. The distance between the fish anode and the prop is about 4 feet.The fish was bolted to the pushpit base stud which was in turn permanently attached directly to the battery negative pole and the connections were good. The vessel is GRP, is not bonded and has a single anode. There has been no wear at all in the fish anode during the 6 months. I dived on the shaft anode the other day and it was hanging loose on the shaft well over 50% eroded whereas the last time I inspected it 2 months ago it was still fully intact. In other words the hanging the anode over the side was a waste of time as protection against galvanic corrosion as distinct from electrolysis. Is there any point in an 'over the side anode' in an unbonded vessel?
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Old 21-12-2012, 08:30   #20
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Re: Hanging The Fish Zinc In The Marina Trick

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Originally Posted by Rietsail View Post
I fitted an 'over the stern' fish anode 6 months ago, for marina use, at which time the shaft anode was completely intact. The distance between the fish anode and the prop is about 4 feet.The fish was bolted to the pushpit base stud which was in turn permanently attached directly to the battery negative pole and the connections were good. The vessel is GRP, is not bonded and has a single anode. There has been no wear at all in the fish anode during the 6 months. I dived on the shaft anode the other day and it was hanging loose on the shaft well over 50% eroded whereas the last time I inspected it 2 months ago it was still fully intact. In other words the hanging the anode over the side was a waste of time as protection against galvanic corrosion as distinct from electrolysis. Is there any point in an 'over the side anode' in an unbonded vessel?

Sounds like you made the common mistake of assuming the path between your shaft zinc and external anode is effective. It sounds like it isn't!

There are way too many connections and resistive uncertainties between the two making the external zinc anode useless especially when connected, as many people do, to a convenient location such as a chainplate or shroud.

The most effective method is to either connect the external anode directly to the shaft or when impractical as closely as possible minimizing both the length and number of intermediate connections.
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Old 21-12-2012, 08:33   #21
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Re: Hanging The Fish Zinc In The Marina Trick

The guppy will work, but only if in close proximity to the metal being protected and in almost perfect electrical contact with the metal being protected.

Ours (when I still had it) measured 8" from the prop, and electrically 0.03 Ω from the prop through the negative start battery terminal.
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Old 21-12-2012, 21:18   #22
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Re: Hanging The Fish Zinc In The Marina Trick

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What problems are created with to many zincs?
In wooden vessels it is possible to cause deterioration to the wood in areas such as where through hulls are located. There was an interesting article about this some years ago in (I believe) Wooden Boat magazine.
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