Zinc Anode Quality Differences?

[BBB2boater]

My 1987 200HP Evinrude is used in saltwater and has had corrosion problems for some time now. The zincs are keep clean and shinny (they last a long time - I just shine them up each year!). I regularly check electrical contiunity between the zincs and all engine parts and the electrical path is very good. Areas of the lower unit where paint has been worn off always show significant corrosion (white powder formation). After scratching my head for several years about this problem, a friend suggested zinc 'quality' is the problem. He claims some zincs are of low quality (don't sacrifice themselves first and allow the engine to corrode) and some are of high quality (sacrifice themselves quickly). Does anyone have any knowledge about zinc quality? If so how would I select and where could I purchase a 'good quality' zinc? Or is my friend wrong and if so does anyone know what is causing this corrosion problem? By the way I have a stainless prop if that matters.

 

[DJ]

Re: Zinc Anode Quality Differences?

I don't know where you got your zincs, but you can't go wrong with OEM (genuine) parts.<br /><br />When you say "shine them up", what do you mean? If anything, sand them rough.

 

[umblecumbuz]

Re: Zinc Anode Quality Differences?

Your friend is right - sort of.<br /><br />'Zincs' are not made out of pure zinc - they are a mixture of metals of which zinc is the predominant metal. So 'zincs' can vary in their sacrificial value.<br /><br />If you're having corrosion problems on your leg even though you take care of your anodes - and to clean off the white, furry-looking deposits so that bare metal shows through is correct - then it's time to find out why, and the anode mix could be the reason. <br /><br />You haven't said if your boat stays in the water or is trailered. If it stays, is it in a marina? If so, are other boats having corrosion problems? If they are, then you may have a marina current leakage, or a nearby boat with bad wiring connected to shore power.<br /><br />If you're on your own, then change your anodes. It might mean a bit of investigation locally to find anodes that sacrifice faster, but it'll be worth it. And yes - a stainless prop could cause lesser metals nearby (the leg) to corrode faster. Not saying it does - but the ingredients are there.

 

[Dunaruna]

Re: Zinc Anode Quality Differences?

One of the tests you can do is probe the water around the boat for voltage, it can indicate the area of concern. Anything over 1 volt should raise alarm bells.