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Old 20-04-2009, 23:36   #1
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zinc only last half a season

hey everyone,
My zinc attached to my propeller and it is a 30mm zinc. It only last half the season (about 2 months) is this normal.. can i just buy a 60mm. We bought the boat used and the previous owner used 30mm. im not sure if its okay to chance size etc
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Old 22-04-2009, 05:19   #2
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I would start looking at your wiring. It sounds like you may have some stray current running around. There are more people on this forum who may have a better answer but a zinc should last longer than that.
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Old 22-04-2009, 07:11   #3
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Erosion of the shaft/prop zinc is typically caused by one of two scenarios: stray current around adjacent boats from an improperly or poorly grounded shore power circuit or stray current induced from a bad or corroded ground on your boat. If you are on a mooring, obviously the first cause is moot.
Fixing the problem is not that easy to explain as it depends on what circuit(s) is/are dysfunctional and can only be identified by examination.

If you are constantly connected to shore power and do not have an isolator or isolation transformer, there are simple tests to determine a shore power ground fault which bears reading up on.

If you are constantly on a mooring, start inspecting all your wiring for a bad ground starting with the bilge pump wiring and the existence of any voltage potential between separate grounds on the boat.

Without knowing more of the above, it's impossible to pinpoint the problem which can be causing more damage than simply eating your zinc. Simply putting on more or a bigger zinc will only serve to exacerbate the problem.
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Old 22-04-2009, 08:25   #4
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Are you plugged into shore power 24/7? Could be another boat is leaking the current and you're just the unlucky boat in the path. Make sure your shore power is wired correctly. If it is, you may have no fix until the offending boat is corrected. A galvanic isolated on your shore power helps..
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Old 22-04-2009, 10:25   #5
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As mentioned...It's either your boat's AC set up or a neighboring boats set up. Have the harbor people look into it.
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Old 22-04-2009, 13:57   #6
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Try unplugging your boat.
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Old 23-04-2009, 00:12   #7
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I am going to rule out the problem coming from another boat because we have had the boat for 2 years and we were in different locations with different boats next to us. We are plugged in 24/7 while we are away from the boat (mostly weekdays). I should point out that the previous owner of the boat was a big electrical guy. He was some sort of engineer. Anyway he had one 30amp line running everything onboard which included A/C. I don't know how but he made his own splitter box and one line powers everything. Maybe that has something to do with it. Also I do feel like our 2 optimas don't last as long as they should. With gps, depth, wind, cb, an refrig on it lasts just over 2 hours.. Maybe its all do to the same problem? Where can I start to check?
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Old 23-04-2009, 08:59   #8
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Electrolysis and low battery capacity are always mutually exclusive problems.

What is the rated capacity of your batteries? Connected in parallel? Charging equipment and rating? Need more info before making even a guess as to why your batteries are problematic but it is clear any reasonably sized batteries should handle the electrical demand you cited for at least a full day ot two before recharge is required.

With respect to the electrolysis, I am an engineer and know some stuff about electronics but marine electrical circuits are fundamentally different from typical electrician-type knowledge which may be your first problem - that of the previous owners handiwork. Can't know though but most electrolysis issues arise from faulty AC wiring, not DC..

you might receive lots of guesses and suggestions here but chasing your tail can get frustrating and time-consuming so you might be better served by wither reading up on marine electrical systems or hiring a reputable marine electrician to inspect you wiring, installing a galvanic isolator and load-testing your batteries and verify your charging system is (charging properly).
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Old 24-04-2009, 06:27   #9
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I don't all the specs off the top of my head. I will get them together this weekend and post them. thanks
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Old 24-04-2009, 07:46   #10
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Before you start chasing all sorts of possibilities, you need to measure your leakage current of your own boat. Using a multimeter, connect the negative terminal to your boats ground. Connect the positive terminal to a small wire which at the end you attach a piece of silver (something about the size of a quarter will work fine). Set the multimeter to measure milli amps. Drop the wire with the silver over the side of your boat into the water and see what current the meter displays. For most sailboats you want about 700-800ma of current. If your current is low, you need to add more zinc. Start with everything on the boat turned off and slowly turn things on and you can see which item on your own boat may be causing a problem. If you need more Zinc, you may want to add one to the hull wired to your ground system. This is what I ended up doing and all my problems went away. To help calculate what size zinc you will need, I picked up a bunch of small zincs and started by attaching a wire to one connected to my ground and drop the zinc over the side of the boat. I kept adding more zincs until my mulitmeter read 700-800ma. I then knew how large of a zinc the boat needed.

I hope this helps.
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