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post #1 of 6 Old 04-27-2019 Thread Starter
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Zinc and Outboard

I have an outboard in a purpose-built well whose leg remains submerged in Beverly Mass harbor at all times. After 1.5 seasons the single zinc has dissolved entirely. It was not large, perhaps the size of 3 or 4 stacked nickels.

Then, the SS machine screw that secured the zinc seized and sheared when I tried to remove it, so now I have a sheared SS stub need a new zinc solution.

1. Moored 3/8 of a mile from the nearest land-powered marina, what might have caused my zinc to dissolve? Anything on my boat I can repair? It is a simple 12 volt only system with no shore power components.

2. I plan to leave the sheared machine screw alone and attach bigger zincs with newly drilled holes and bolts in a different area of the outboard's leg. Given this engine is an auxilliary that may only run 20 hours per season, is there any real problem attaching zincs most anywhere under the waterline? I want the protection but do not care if it degrades motoring performance by 1/10 of a knot.

Thanks for you thoughts.
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post #2 of 6 Old 04-27-2019
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Re: Zinc and Outboard

Another possibility is a good sized zinc on a stainless steel cable. The cable can have a hook on the opposite end which you hang on some bare metal on the motor. Easily removed when you go sailing.
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post #3 of 6 Old 04-27-2019
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Re: Zinc and Outboard

The zinc is suppose to dissolve away. 1.5 seasons is a long time for a small outboard zinc.get a larger aluminum alloy anode and you can attach anywhere under water. the aluminum will last longer then zinc and will protect the outboard better then zinc. good for salt and brackish water. go with the newer technology and help the environment at the same time

https://www.boatzincs.com/zinc-vs-aluminum-chart.html

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post #4 of 6 Old 04-28-2019
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Re: Zinc and Outboard

Sounds like the anode is working and that's a long time for one anode. Personally, I would just try to replace as designed. Drilling holes into the lower gear unit sounds ominous. I suppose you could be sure you don't penetrate the internals, but one never knows if there is an odd passage cast into the leg somewhere. You'd also need to know you were not inadvertently choosing a location that was insulated from other underwater parts, or the anode wouldn't work. I'm sure you'd figure these out, but I'd just do it right.

If you can't figure out how to get the stub out, post a pic and someone will have a good idea.


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Re: Zinc and Outboard

BTW, a larger anode is not necessarily better.


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Re: Zinc and Outboard

Rare to find a motor with only one zinc so it may be time to check the owners manual to vet out the others in the water jacket, etc. Yamaha for example can have a zinc for each cylinder in the head, one on the skeg and another one or two near the mounting bracket.

If the outboard motor is left in the water then the zincs should be checked around 2 to 4 times a year. The zinc does need to come into good direct electrical contact with the metal on the motor when you replace it too so cleaning up any corrosion with a wire brush to reveal clean metal on the motor is a critical step that way too many skip when replacing zincs.
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