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  #1  
Old 05-21-2009
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Another zinc question

Hi,

I'm a brand spanking new boat owner with very limited experience operating a boat.

I understand (I think) what a zinc does and why. My question is where a zinc should be connected to the boat when in the slip. Currently my boat has a "guppy" zinc that is attached to the backstay attachment on the transom with a clamp. Does that allow the zinc to do it's "job"? Should the zinc be connected to the engine?

Thanks.
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  #2  
Old 05-21-2009
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Your boat should have already installed zincs in two or more places. One on the drive shaft and one in the heat exchanger. From your post it appears that you are referring to an external zinc that you drop overboard. If it makes you happy, use them but make sure the installed ones are good first.
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Old 05-21-2009
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Hi Dave,

You will need to bond the zinc to the propeller assuming that is what you are protecting. It is unusual (though not impossible) that the rigging is connected electrically to the underwater components. You could check that with a multimeter. Assuming the guppy is on a wire with a clip at the end, then clip that to the engine, or drive shaft, or any component that you know to be in electrical contact with the underwater components to be protected. If you know that your rigging is bonded to common ground then you can leave it as is.

As Dwayne mentions, these anodes are usually less effective because of poor electrical contact than the proper zincs that are installed in hard contact on the propeller shaft, or on the engine, but they fall under the "can't hurt" category.

Wayne

Last edited by wwilson; 05-21-2009 at 09:25 PM.
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Old 05-22-2009
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There is a collar zinc on the prop shaft. The guppy is in addition. The row of slips I am in at present is reputed to be "hot" according to a local.

I was thinking it would be better for the guppy to go to the engine/prop shaft in order to provide protection there.

Thanks for the help.
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Old 05-22-2009
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My $0.02... Electrically speaking, the over-the-side guppy zincs are pretty close to ornamental. Give it to someone to display on shore. Properly attached zincs will work 10x better, and you won't have that "Irish Pennant" over the side.
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Old 05-22-2009
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Be somewhat cautious regarding advice as this may seem like a simple issue lots of folks talk about, it gets more complicated once you start adding zincs indiscriminately.


Keep in mind that the zinc will CREATE electrolysis (favorable electrolysis since the zinc is being eaten up). Putting zincs where they were not needed will still cause the zincs to erode away since they create the battery situation where none may have existed.
The range of protection a zinc can supply to other metals bonded to it is limited by the conductivity of the water. In salt water you get coverage for a radius of about 4 to 6 feet. A zinc on the stern of a 14 ft boat where everything is bonded is only protecting half the boat. This range gets even less in fresh water and may reduce to only inches. Often magnesium is substituted for zinc in fresh water to provide an even higher voltage to push through the fresh water.

Generally, electrolysis problems are created by the shore power connection. You could theoretically disconnect the ground connection in the shore power and avoid electrolysis (and in some cases this is a solution). Alternatively, the use of a galvanic isolator can often cure an electrolysis problem induced by shore power issues.
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Old 05-23-2009
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The term hot slip refers to a shore power electrical problem where the boat may be hot from improper grounding. Isolation transformers can be used to prevent this from occuring and to help isolate your boat from their problem. Additional zinc can help if it is attached through a gounding grid to the engine/prop shaft to complete the circuit. The lower the resistive path the better.
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Old 05-28-2009
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SailAK - I think you'll find the attachment point where the guppy is clamped on the transom is grounded internally to the engine.



Dave
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Old 05-29-2009
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Be aware that connecting a zinc to the engine via the stainless steel backstay and chain plates is going to compromise its effectiveness, as the stainless steel is a fairly poor conductor of electricity.
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Old 05-29-2009
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Good point. I just wanted an out-of-the-boat connection point for the guppy. I could have probably done better.

Thanks.
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