On my boat the shaft zinc seams to last about 3 months. If I install two zincs on the shaft will they last twice as long? Can you put too many zincs on a shaft?
shaft zinc
- Thread starter Hayden Watson
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I typically put two zincs on my bronze shaft and they last the 8 months that my boat stays in the water each season. If your zincs are not lasting for 3 months, it would pay to find out why. It may be that you have more than normal ambient electricity in the water where you keep your boat. That could be caused by improperly grounded power stations on the dock -- or by electricity dribbling off nearby boats. It is also possible that you have an AC or DC current leak on your own boat. I recently exchanged email about the latter issue with Don Casey. See below.
Your original question:
Last year the zinc anode on my bronze shaft of my sailboat was about 75 per cent dissipated at the end of the season. I had connected to shore power only for about 10 hrs the whole season. Thinking I would gain protection this season, I put on two zinc anodes. When hauled a few weeks ago, both anodes were equally dissipated also to about 75 per cent gone. Only this season I never connected to shore power at all. Does it make sense to double the number of anodes? Would agree that the problem would seem to be ambient electricity in the water at my marina? What else could cause this problem? Thanks.
Our expert's answer:
Current flowing to your boat from an outside source would indeed eat away your anodes, but this requires a complete circuit, meaning your boat would need to be plugged in to the shore circuit. A more likely scenario is that your shaft is connected to the ground side of your electrical system through the ground lug on your engine, and somewhere in your electrical system is a small ground-fault that is energizing the shaft. This assumes that you feel confident that the anodes are not sacrificing themselves simply due to dissimilar metals in the water, given that your shaft is bronze rather than a steel alloy. There is also the issue of what alloy these anodes are compared to the one you had installed last year. Not all anodes are the same on the galvanic scale, which will affect how long they last.
This seems like a case where you should check all of your onboard circuits for leaking current. You can find instructions for doing that in Sailboat Electrics Simplified. If this effort does not reveal a current leak, then the recommended treatment is what doctors now call watchful waiting. Put on fresh zincs and keep an eye on them.
Your original question:
Last year the zinc anode on my bronze shaft of my sailboat was about 75 per cent dissipated at the end of the season. I had connected to shore power only for about 10 hrs the whole season. Thinking I would gain protection this season, I put on two zinc anodes. When hauled a few weeks ago, both anodes were equally dissipated also to about 75 per cent gone. Only this season I never connected to shore power at all. Does it make sense to double the number of anodes? Would agree that the problem would seem to be ambient electricity in the water at my marina? What else could cause this problem? Thanks.
Our expert's answer:
Current flowing to your boat from an outside source would indeed eat away your anodes, but this requires a complete circuit, meaning your boat would need to be plugged in to the shore circuit. A more likely scenario is that your shaft is connected to the ground side of your electrical system through the ground lug on your engine, and somewhere in your electrical system is a small ground-fault that is energizing the shaft. This assumes that you feel confident that the anodes are not sacrificing themselves simply due to dissimilar metals in the water, given that your shaft is bronze rather than a steel alloy. There is also the issue of what alloy these anodes are compared to the one you had installed last year. Not all anodes are the same on the galvanic scale, which will affect how long they last.
This seems like a case where you should check all of your onboard circuits for leaking current. You can find instructions for doing that in Sailboat Electrics Simplified. If this effort does not reveal a current leak, then the recommended treatment is what doctors now call watchful waiting. Put on fresh zincs and keep an eye on them.
Haden its a book
Sailboat Electrics Simplified.
At Shilshole I go about 8 months between zincs, on shorepower 90% of time. Two on the shaft and one hub zinc behind the prop on the end of the shaft. I also have a fish zinc, ( zinc hanging in the water and wired to engine) which lasts a year or so.
I think the Puget Sound norm is about 6 months
Sailboat Electrics Simplified.
At Shilshole I go about 8 months between zincs, on shorepower 90% of time. Two on the shaft and one hub zinc behind the prop on the end of the shaft. I also have a fish zinc, ( zinc hanging in the water and wired to engine) which lasts a year or so.
I think the Puget Sound norm is about 6 months
Kind of hard to say
Since I don't know your area it's kind of hard to be specific, but I believe that if a zinc didn't last more than three months I would be looking for a cause. There is some stray current around there somewhere.
Since I don't know your area it's kind of hard to be specific, but I believe that if a zinc didn't last more than three months I would be looking for a cause. There is some stray current around there somewhere.
Re: Kind of hard to say
I am just north of Seattle and I also am hooked up to shore power most of the time. I have a galvanic isolator installed so I do not think my problem is from the shore power.
One strange thing is that the prop zinc I get from AutoProp usually lasts 1½ years. I have had a dive service cleaning my hull and replacing the zincs. I do not know what brand they use but they tell me they are “gone” every time they dive it which is 4 times a year. Does it make a difference what zinc you use? The AutoProp zincs are very shiny.
I used to have the boat in a fresh water lake and both zincs would last several years.
I am now diving the boat myself and will be installing a zinc I got from west marine. It will be interesting to see how long it lasts.
I am just north of Seattle and I also am hooked up to shore power most of the time. I have a galvanic isolator installed so I do not think my problem is from the shore power.
One strange thing is that the prop zinc I get from AutoProp usually lasts 1½ years. I have had a dive service cleaning my hull and replacing the zincs. I do not know what brand they use but they tell me they are “gone” every time they dive it which is 4 times a year. Does it make a difference what zinc you use? The AutoProp zincs are very shiny.
I used to have the boat in a fresh water lake and both zincs would last several years.
I am now diving the boat myself and will be installing a zinc I got from west marine. It will be interesting to see how long it lasts.
Has anyone else had a case where the shaft zinc would be gone in 3 months and zinc attached to the prop n that shaft would last for a year and a half?
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