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  #1  
Old 11-26-2007
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Guppy Zinc

I have a guppy zinc hung over the side of my sailboat. I have attached it at a point where I measure the highest current between the lead to the zinc and the point of contact. In my case this is about 0.7 to 0.8 volts on a stanchon. Is this the best way to place the extra zinc?

I am not sure if this is helping although since keeping a guppy zinc attached this way I do not seem to have to replace the zincs on the prop shaft as often. Have others found this?

Not entirely clear why the stanchon shows signifcant voltage as I do not see how the connection back to the water is completed. Am I assuming incorrectly that the zinc in this case has to be helping?

Thanks,

Jim
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Old 11-26-2007
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If there is no direct electrical connection to the part for which protection is intended (in your case; the shaft & prop) the guppy zinc will have no effect.
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Old 11-27-2007
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I don't see why your stanchon should have any voltage differential. Where are you measuring the voltage from the stanchon to? I've used the "fish" zinc for a long time but it's connected to a wire lead from my stuffing box (bronze.) Is there any connection to your stanchon to produce the voltage? What's you hull made of? Wood can conduct and if you have voltage at your stanchon you should find the source.
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Old 11-27-2007
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Unless the stanchions are bonded electrically to the engine, prop shaft and other underwater metal on your boat, the guppy isn't really doing anything.

You really do need to find out why the stanchion is "hot". It really shouldn't have nearly a full volt of potential IMHO.
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The sailboat is fiberglass.

I am measuring the voltage from the lead on the zinc with the zinc in the water and the stanchon.

I will investigate further to see if is a connection somewhere to the bonding system and post later.

Jim
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Old 11-27-2007
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Wires are often run in the chase that is the area where the deck connects to the hull. It is also where the stanchons bolt to the deck. I would try and look at your wires. in that chase, you may have a short or a bare wire.
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How likely is it that some or all of the lifelines are electrically connected to that stanchion? My thought is that you're seeing an induced voltage into an "antenna" system. This would not necessarily be an indication of trouble with the stanchion or lifelines but, as above, you are probably not getting any protection this way. Clip the guppy to the prop shaft.
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Old 11-27-2007
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Interesting thought that it could be an antenna effect.

I am not aware of any wiring issues. We live aboard and I am an excessive compulsive checker of systems.

Everything is AOK as of this weekend.

Is there anybenfit to connecting the zinc to a shroud which is in turn connected to the bonded system?
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Old 11-27-2007
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It depends on what you are trying to protect in the sense that the zinc should be in as close proximity to whatever it is to minimize the reisitance. Simple Ohm's Law dictates that in order to increase the efficacy of the zinc, the induced current (NOT VOLTAGE) between the protected metal (prop?) and the anode must be maximized and resistance minimized. As other have already said, it is best to have the shortest unbroken connection between the zinc and prop. If the rest of the boat is bonded, so much the better but it's the underwater stuff which suffers most from lack of protection.
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Old 11-27-2007
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Yeah...connect the guppy to the shrouds or backstay if they are grounded. Doesn't eliminate the absolute need for a shaft zinc but can help.
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