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Old 04-13-2017, 02:38 AM   #1
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Default Mercathode systems

I have a 2001 SCR 2700 with a Brovo III outdrive. There is a lot of boaters having lower unit corrosion problems on our dock. Several people have had to replace their outdrives. We are having many discussions on prevention alternatives.
One question that has come up. Does the batteries have to be in the "on" position in order for the Mercathode system to work?
Two boats sitting next to one another, one with batteries "on", one with batteries "off". The boat in the off position has much worse corrosion.
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Old 04-13-2017, 11:17 AM   #2
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If a lot of boaters are having issues there is a bigger problem than what the mercathode is designed for.

There is either wiring errors with the marina shore power or one or more boats have wiring issues. Have the water tested for stay currents. Note this is also a safety hazard for electrical shock for anyone who may get into the water. A galvanic isolator would be a better solution to protect your boat.
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Old 04-13-2017, 12:24 PM   #3
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You have a problem with stray current at the marina. I would strongly consider moving to a different marina.
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Old 04-13-2017, 03:20 PM   #4
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What they said.
But to answer your mercathode question, you might have to go check the wiring. Mine are wired directly to the batteries, but I don't know if that was factory or not.
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Old 04-13-2017, 04:13 PM   #5
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It should not matter the battery position.

My marina on Lake Powell has implemented a no swimming policy but I have not heard of any accelerated corrosion of outdrives.
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Old 04-13-2017, 04:49 PM   #6
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Quote:
Originally Posted by Phillbo View Post
It should not matter the battery position.

My marina on Lake Powell has implemented a no swimming policy but I have not heard of any accelerated corrosion of outdrives.
If just one boat has polarity reversed, whether it be the wiring on the boat or in the dock outlet, it can cause accelerated corrosion for everyone on the dock connected to that power.
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Old 04-14-2017, 12:41 AM   #7
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You would think they would have identified the bad wiring way before their outdrive was eaten up and destroyed.
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Old 04-14-2017, 12:52 PM   #8
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Keep in mind that shock to a swimmer due to stray current is really a freshwater phenomenon. That doesn't occur in saltwater. Corrosion of aluminum, however is more of a saltwater problem and is not as prevalent in freshwater.
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Old 05-11-2017, 12:51 AM   #9
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Wahweap always had a no swimming policy. Not always well enforced.

My mercathode is connected through the battery switch, since it picks up power through the engine harness.

If the marina or another boat has an issue, that can be very hard to track down.

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Old 05-11-2017, 12:55 AM   #10
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Quote:
Originally Posted by shrew View Post
Keep in mind that shock to a swimmer due to stray current is really a freshwater phenomenon. That doesn't occur in saltwater. Corrosion of aluminum, however is more of a saltwater problem and is not as prevalent in freshwater.
Interesting comment, never really thought about it. We had some swimmer (my mother and sister mainly) get heavily shocked on lake Powell while we were working on the electrical system on the houseboat. That was in fresh water.

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