Info from Mercrusier about corrosion

dicor

New Member
Feb 19, 2011
835
boat Barnegat Bay, NJ (hopefully) - live Bucks Cty
Boat Info
270 DA 1998
Engines
7.4 Merc w/Bravo III Drive
I have a BravoIII so I need to do what I can to protect against corrosion. I've seen a lot of info floating around but decided to call Mercury for the straight scoop.
  1. Don't add a second Mercathode if you only have on engine, it's counter productive. One will do the trick.
  2. If your setup did not come with a anode on the prop nut don't add one. Too many zincs will begin to have the out-drive casing protecting the zincs.
  3. If you are painting your out-drive per paint manufacturers directions whether, Interlux , Petitt or whoever paint the bare metal that is normally covered by the inner prop. This is hard to explain. If you remove both props you will see about 5 inches of unprotected metal, Mercury does not paint it from the factory. I'm not referring to the shaft. This exposed metal should be painted especially if your in saltwater.
  4. Get a Merchathode test probe & Digital Multimeter, learn how to use it and check for stray electricity often.
I hope this helps.
 
Interesting. When i questioned my dealer about the carrier (the 5" under the inner prop) I was told to definitely not paint that part even though It showed some corrosion. Seems like paint would help as you noted.
 
If your setup did not come with a anode on the prop nut don't add one. Too many zincs will begin to have the out-drive casing protecting the zincs.

I would love to know exactly who at Mercury said that.

A engineer at Mercury told me the opposite.


Edit: after making a phone call I have a possible explanation for the confusion. Some people were drilling and damaging the hardened steel propeller shaft in an attempt to modify the shaft to accept the 2004 and newer propeller anode. There is no issue with the nut mounted center anode method.
 
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I called Mercruiser support at 920-929-5040. The way he explained it was that if you have too many sacrificial anodes the result is that the aluminum out-drive will begin to protect the anodes and begin to corrode. Don't ask me how or why.
I found this explanation below on the internet, the explanation is not from Mercruiser:
Having too many anodes can repel the metal-based anti-fouling around the shaft logs,
rudders and water inlet fittings, connected to the zinc. It’s like putting ‘like’ poles of a
magnet together. They will repel each other, which is leaving unprotected areas.
 
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I called Mercruiser support at 920-929-5040. The way he explained it was that if you have too many sacrificial anodes the result is that the aluminum out-drive will begin to protect the anodes and begin to corrode. Don't ask me how or why.
I found this explanation below on the internet, the explanation is not from Mercruiser:
Having too many anodes can repel the metal-based anti-fouling around the shaft logs,
rudders and water inlet fittings, connected to the zinc. It’s like putting ‘like’ poles of a
magnet together. They will repel each other, which is leaving unprotected areas.

Why do they put the second anode on the cavitation plate and the prop anode on in the second Brabo III generation.
This is my boat when I bought it....and it was moored in fresh water.
00260DABIIIO-D11-15-07.jpg

00260DABIIIO-D11-15-072.jpg

The new one looks much better because I trailer it. If I had the boat moored in fresh or salt, I'd pull it to check once a month. They're too expensive to do otherwise.
 
When I purchased my boat this fall, the PO was pulling it to paint the bottom and outdrive. Freshwater only boat. I asked him to have the marina to check the outdrive for corrosion. There was. Seems the docks where he slipped the boat were metal and that with whatever was happening at the dock caused the corrosion. New outdrive was put on. Good for me. Had the marina mechanic check the Mercathode system and it checked out as working.
I guess where you keep the boat in the water is going to have a lot to do with corrosion issues no matter what you do to prevent it. Or at least slow it down.
 
Stray current at the dock is a big issue. If a boat nearby has a dead battery for a week or a dangling wire, that's all it takes. I've decided to by the mercury test probe and check stray current often for now on. These Bravo III out-drives turn into Alka Seltzers in a matter of months if galvanic corrosion gets hold.
 
On the Mercathode, by all means do electrical tests. That being said, don't ignore a plain old fashioned visual inspection. When we first got our boat it was eating zincs. I discovered that although the mercathode tested aok, it did not seem to being doing the job. It turns out that somebody who did the bottom painting for the PO painted over filament. After it was cleaned with acetone it worked as it was supposed to.

Henry
 
This bring up another question barnacles are a big issue where I dock. If or in my case when the Mercathode gets covered in barnacles does it become ineffective? Or does the current pass right thru those little bastards? I don't think there is a recommended way to scrape barnacles off the Mercathode without damaging it..
 
I don't think an additional anode would have prevented what happened to your out-drive. That looks like the Mercathode wasn't working or you got a lot of stray electricity at the dock or both.

On the Mercathode, by all means do electrical tests. That being said, don't ignore a plain old fashioned visual inspection. When we first got our boat it was eating zincs. I discovered that although the mercathode tested aok, it did not seem to being doing the job. It turns out that somebody who did the bottom painting for the PO painted over filament. After it was cleaned with acetone it worked as it was supposed to.

Henry

Yeah, well I guess my point is that this can happen in moorages in fresh or salt water. Taking for granted that everything is hunky dory in one month can change quickly as soon as someone new moves into your moorage and their systems are not in order. When I bought this boat, exactly 4 years ago tomorrow, the boat had 94 original hours on it, the previous owner hardly used the boat but he had already replaced the OD in 2003. So in 7 years at the time the boat was going tobe on it's 3rd outdrive in 94 hours. I don't think and extra anode would have prevented this. It was and still is a very "hot" marina. In Seattle this is near Gasworks park, which is notorious for intense industrial activity @ the turn of the century. There is tons of metal in this area, acting like giant battery. I'm just glad to not have the $20k bill for two outdrives.....not knowing why that was happening.
 
I wish I could find step by steps on testing the mercathode system....

I have 13 year old bravo 3's that are starting to show their age, and it's hard to tell if the mercathode system is still protecting. We added the prop nut anode (your post is the first I've seen saying not to!)

I also think my drives are missing some of the grounding straps.... Which may be causing issues....
 
I wish I could find step by steps on testing the mercathode system....

Here ya go...

http://www.*******.com/merc/Servmanl/6/6A7R3.PDF

Easy to do. You will need a voltmeter and a silver reference electrode like the one below:

http://www.reliabilitydirectstore.com/RDI-CRE-Corrosion-Reference-Electrode-p/rdi-cre.htm

Or you can buy the mercruiser branded silver reference electrode which is about $40 more and there is nothing special about it. A silver reference electrode is all you need. Nothing special about the mercruiser branded one. RDI also has a very informative PDF on the bottom of the order page.

John
 
The *** are b*o*a*t*f*i*x. Not sure why the link changed. If it is one that should not be posted then moderator please delete it.
 
Click here: http://www.mercstuff.com/mercathodetest.htm for a step by step procedure. It's pretty straight forward.
I'm debating on whether to buy the test probe from Reliability Direct which is $20 cheaper and looks as if it's built sturdier or buy the one Mercury recommends. I'm leaning towards the Mercury probe because I can see it now, next season I test the system with the non Merc probe and it will be out of spec then I'll be sitting there scratching my head wondering if it's because it's the wrong probe or actual stray current.
 

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