Mercathode - There has to be a better way to make sure it is working

D

Dave S

Well-Known Member
TECHNICAL Contributor
Oct 3, 2006
6,014
Upstate South Carolina
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This posting is more for Mercury (assuming they read boating message boards) than anything else.

In my opinion, when the Mercathode system is not working properly because of a component failure such as the Mercathode control box or the transom unit or (in my case) the additional mercathode pucks I added to my transom, then the ECU should be able to detect this and report the failure to the owner thru the Smartcraft system. Today the only way you can determine the system is or is not functioning today is to buy a tester like this http://www.mercurypartsexpress.com/us/index.php?target=products&product_id=217965 And if you don't have one of these units and use it regularly then you will never know if your system is working correctly. And just because you test it and think it is OK, there is no guarantee that something might fail the next day and you wouldn't be aware of it until you tested again.

I don't have a tester but I do ask my dealer to check mine at least once a year. The last time they checked it, it was "within spec" but it showed a much lower reading on the port side. When my boat was out of the water for it's spring clean up. I was appalled by the corrosion on the drive. When I pulled my props, the bearing carrier was also severely corroded.

IMG_0131.jpg


The port transom anode was overgrown with growth........ a sure sign it had failed (but who knows when :smt021). I had the dealer replace the anode and I sanded and painted the drive. But the net result of this failure is my bearing carrier has suffered some serious corrosion. Up until this last haul out, I had not had a corrosion problem for almost two years. My point is it should not be a surprise to an owner when he pulls his boat out of the water every six months and discovers corrosion. The Mercathode system should be self checking as far as I am concerned and should be alerting the owner of a problem thru Smartcraft when it occurs.
 
My carrier looked worse than this and Mercruiser replaced both lower units under warranty (I just made it before 2 years were up). I agree that there should be some way for the system to automatically monitor Mercathode function however stray current in the water can also erode the drive even when the Mercathode is working correctly.
 
This is my second lower unit. The first was replaced by Mercury under warranty a couple of years ago because of similar corrosion particularly on the bearing carrier. All I know is this appears to be a losing battle with no good resolution on how to stop this problem in the future. I meticulously maintain my boat and my outdrive. I pull the boat out of the water every six months and paint the outdrive if there is any corrosion on it. The last time it was out of the water the drive had only minor corrosion with virtually none on the bearing carrier (which is why it is unpainted in the picture above). So far Mercury is not inclined to replace the lower unit again.
 
Lets face it, the BravoIII has/is a major design flaw, I don't care what spin anyone puts on it. Too many dissimilar metals creating galvanic corrosion at an alarming rate. They are designed for freshwater, put them in saltwater, tie the boat to a slip then watch them turn into powder. The Mercathode, in my opinion was an afterthought, I can imagine the Mercury engineering department frantically scrambling around to come up with a way to correct this flaw and here we go the birth of the Mercathode. I see plenty of boats with Alpha drives tied at the slip in saltwater for years with only the standard anodes protecting them, no problems. These Bravo III drives are making a fortune for those that profit from repairing and selling them, this is what they are best at.
I had to pay Mercury over $100 for a crappy test probe that looks like a cheap children's toy that is used only for measuring the MV in the water produced by the Mercathode. I bought the test probe not only to verify that the Mercathode control unit is still producing voltage but I also need to verify correct output when the barnacles begin to attach themselves to the outdrive and Mercathode. Who knows if it still works all covered with crude, then who knows if it will be damaged if I need to clean it mid season.
 
I brought my out-drive home at the end of last season and over the winter worked on it. I sanded it and within minutes (too avoid oxidation) painted it with Interlux Primco (3 coats 1 week between each coat) then painted it with Interlux Pacifica Plus (again 3 coats 1 week apart). At the end of this season if there are signs of new corrosion on my OD I can honestly say that I did everything I could to prevent and will probably look for another boat with a non Mercury OD. I'm really hoping this works because I have the rest of the boat exactly the way I want it.
 
duckmnn said:
Can you paint bearing carrier?Couldnt hurt could it?Mine looks about the same shape fresh water only.Its on wet slipped about4-5 months and anodes and paint is every year thing.
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Yes................I primed and painted it. It is made out of aluminum but has some type of coating on it that is supposed to inhibit corrosion.

Dave
 
DICOR................I really don't think that any paint we can apply as DIYourselfers will stop the corrosion. It will only slow it down. The factory paint is better than anything we can do at home but it still bubbles and corrodes from the electrolysis effect of aluminum and stainless. I change my anodes every year as well and they take the brunt of the corrosion IF the Mercathode is working properly.

Mercury could probably nip the corrosion in the bud if it put aluminum props on the B3. But my understanding is aluminum is not strong enough to stand up to some of the forces generated on the props by larger boats. I have also seen a number of threads where some people have coated their SS props in the hopes of slowing down the electrolysis.

All I know is when something fails on the Mercathode, you shouldn't have to find out six months later by looking at a bunch of corrosion on that expensive lump of metal that propels your boat. That's why I am advocating that Mercury try to develop some type of failure warning. It may not solve all the corrosion issues caused by stray currents and the like but it would be a step in the right direction.

And it also puzzles me why Mercury hasn't made Sea Core their only offering if it is superior in corrosion resistance.

Any Sea Core owners out there who can tell us what they have experienced?
 
I installed the High Output Mercathodes on my boat last summer. With the standard Mercathode I tested right at the low end of the acceptable range. There is a lot of stray current in my marina. I noticed a big improvement in the amount of corrosion when I hauled the boat this spring. The mechanic that installed the new Mercathodes mentioned that he previously worked for Hall Marine at Lake Wylie. He said the marina there had huge amounts of stray current and that many owners upgraded the Mercathodes due to corrosion issues.
 
I would agree it would be nice if Merc could put some type of sensor in the water to measure the electrical current. The issue is the sensor will draw even more current to the boat. It is physical fact the electrical current follows "the path of least resistance."

If you like to know how to perform the test here is link: http://www.mercstuff.com/mercathodetest.htm. This same site has additional information for those of us lucky to have the Brovo IIIs http://www.mercstuff.com/bravo3corrosion.htm

Also, found a thread where a fellow boater and DYIer repainted his Brovo III. I think he really needed to take the outdirve off and paint the drive and gimbal assembly separately. He is going to miss areas that have he should paint. Also, he states that Merc instructed him to used some automotive products. I am not sure I agree because I don't know how well those will hold up in a water environment. I have heard of guys doing this same process but using tractor paints having success. Tractor preps, coating and paints can take several days to cure and are design to be exposed more so than automotive paints. I can understand why someone may consider using it on an outdrive. Here is the link to his project: http://www.boatingabc.com/forums/ubbthreads.php/topics/484140/1.html I should also note in the end he did not go with automotive paint but got his paint from supermarince.com
 
Jim T - I also have the high output controller along with the transom anodes and my boat is slipped at Lake Wylie Marina. And this lake is really bad when it comes to corrosion.

Dave
 
Fact of the matter is no stern drive boat should be stored in the water for long peroids of time. Stern drive boats should be on a trailer, on a lift, or in high and dry. IMHO if you want to keep the boat in the water buy an inboard.
 
kevin27 said:
Fact of the matter is no stern drive boat should be stored in the water for long peroids of time. Stern drive boats should be on a trailer, on a lift, or in high and dry. IMHO if you want to keep the boat in the water buy an inboard.
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Get to work you slacker!
 
I agree with the 'is it working' portion of this post. My boat doesn't have Smartcraft so that wouldn't help me BUT, could there at LEAST be an LED somewhere so we could verify the circuit is complete? Since its a DC component, I've been thinking of wiring an LED into the actual electrode circut to so that if is ON, I'll at least know that the unit is functioning. It really looks like a rinky dink device, a paper clip sized piece of wire to do the job. A little marine growth and its inerted.
 
Do all B3's have this? Anyone have a picture of it mounted on the outside of their boat?
 
Perry you caught me surfing at work. Got to go. Wait a minute shouldn't you be waxing the boat and not surfing too?
 
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