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Old 27-11-2006, 05:12   #1
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Sacrificial Anodes

I am now keeping my sailboat about 10 miles up the CT river. So it is moored in fresh water but sailed in salt water. What type of anode should I use in my heat exchanger and on the outside of the boat?
Zink, Alum or Mag??? I am very confused on this.
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Old 27-11-2006, 06:35   #2
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Continue to use the same type of anodes you have been using if they have been working effectively for you. It is not the water you are in (except for protecting aluminum outdrives) but the type of metal you are protecting that matters.

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Old 27-11-2006, 06:37   #3
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Mike, a zinc or magnesium anode would be best, as they are more "sacrificial" than Aluminum. I'd choose zinc because of its availability. Just go by a West Marine (or into that store they have up at that marina you're at) and buy a "zinc fish." It's a large annode designed to last the winter. Connect this properly to your electrical system (ground/bonding) and toss it over the side for the winter. Periodically check the "fish" to see if it's still there during the winter. It will slowly deteriorate as it is used up.

Also, be sure your prop shaft has the proper zincs on it. Your heat exchanger won't be so critical as you probably aren't running water through it much this winter?

The good news is that up in the fresh water, there will be very little galvanic action as compared to salt water.
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Old 27-11-2006, 07:06   #4
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There are all types of metal/alloy grades to confuse the situation but convention in the marine industry has always been zinc in saltwater and magnesium in fresh water (especially on aluminum outdrives & outboards).
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Old 27-11-2006, 09:55   #5
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Quote:
Originally Posted by ssullivan
Mike, a zinc or magnesium anode would be best, as they are more "sacrificial" than Aluminum. I'd choose zinc because of its availability.
Anodes are not made of a particular material for no reason. As previously mentioned, zinc should be used in a saltwater environment, magnesium in a freshwater one.

Quote:
Originally Posted by ssullivan
Just go by a West Marine (or into that store they have up at that marina you're at) and buy a "zinc fish." It's a large annode designed to last the winter. Connect this properly to your electrical system (ground/bonding) and toss it over the side for the winter. Periodically check the "fish" to see if it's still there during the winter. It will slowly deteriorate as it is used up.
For any any anode to work, it must be in direct electrical contact with the item being protected. So if your shaft and prop are isolated from whatever the "zinc fish" is connected to by say, a synthetic spacer in the drive line, you will not be protecting them.

You might also ask your neighbors what they are using or call a hull cleaner or prop shop for their recommendations.
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Old 27-11-2006, 11:34   #6
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Yes I agree whole hartedly fstbttms.

You can do a simple continuity test to the shaft and see if there is a good connection. If not, then a shaft brush can be used to connect the shaft with the rest of the engine. However, although "fish" anodes do work and are certainly better than nothing. A major deficit can be had with the use of these. Firstly, you need to have the anode itsself within a few feet of the metal you are protecting. Sometimes not easily done if hanging over the side. Secondly, there must be very little resisitance in the cable used to connect to the metal. So the longer the run, the heavier the cable needs to be, or the resistance in the cable will drop too much voltage, and the metal will no longer be protected correctly. Often in some boats, like fibreglass, that run can be all the way from over the side to down into the engine room, which can be a long way and a pain at being in the road of things like hatches.
Now in saying all that, I use a "fish" as a monitoring anode. It works well. so I am not saying they are entirely bad. Just some thoughts to consider.
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