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Serious Bravo 3 Corrosion problems

The drive is most likely toast. You may get a season or two out of it. The most concerning area is where the prop meets the lower unit. That corrosion will eventually work its way back to where it will cause water intrusion. I purchased a boat with a BIII on it, and when I got it I knew the drive had'nt been taken care of. I limped it along for three years before it gave out, then I replaced it with a newer version, no problems since. The early BIIs had more issues than the later, for a number of reasons. One being the aluminium aloy that was used in some of the early versions (if I remeber correctly 1998ish -2000ish?). If you didnt already know this the BIIs are AWFUL when it comes to corrosion control. It can be done you just need to keep up on your anodes and USE THE CORRECT ONES FOR YOUR WATER CONDITIONS, any Mercruiser authorized facility will tell you what to use. Mercrusier has put out numerous service bultins and such on this issue. DO NOT LISTEN TO ALL THE DOCK TALK on "zincs" and "onion bags full of zincs" and "you must be in a hot spot......." A good Mercruiser rep. will tell you the application you need for your set up. If you dont have a good one in your area a marine ELECTRICAL surveyor can tell you what you need to do to protect your boat then test the boat using a silver/silver chloride reference electrode and a volt meter. The reson the BIIIs corrode so quickly is because it is required that you use stainless props (two of them). When you put that much surface ares of stainless near a less noble metal, the aluminum drive, then submerge it in an electrolyte (out of all water conditions salt water is the best for that) essentially you make a battery. Thats why you need to intruduce the sacrificial anodes, which is aluminium if you are in salt water, so they experiance the loss of electrons (galvanic corrosion). You may get some guys running a BII saying that they havnt had any issues and thay are correct, probably for a few reasons; most are running aluminum props or the owner doesn't keep the boat in the water if he or she does have a stainless prop on it so they think that the problem doesn't exist, it does but its just happening much much slower. Sorry for the long rant when you had a simple question..lol. Im not sure how much of the above you already knew so if you did disregard. But in my opinion the drive is well on its way to being gone. I have never seen someone stop the damage once it has gotten that bad.
 
Improper shore power connections, auto charger instead of marine, electrolsys from a slip neighbor,missing bonds/grounds.
 
If you use shore power install a galvanic isolator, this will prevent 120ac from damaging your boat. It acts as a check valve for 120ac. The only way "stray 120" can damage your boat is if it finds its way back to ground (the marina transformer) the isolator prevents that. I left the bonding straps out of my post but probably more important than the anodes. Its common for a sloppy tech. to forget to put the bonding straps/wires back on, when that happens you can "zinc up" all you want and you will pull your hair out trying to figure out why you have weird corrosion going on. If you want to try and keep the drive you have on the boat for a while I would buy a bulk aluminum plate anodes, attach a cable to it with an alligator clip on one end and hook it to a solid point on the motor or transom assem. or both. When I did that and had my reference electrode in the water you could see the reading on the volt meter change, showing a greater level of protection.
 
Thanks for all the advice. So this is my working plan so far:

This is my first season with the boat and my first time dealing with Bravo 3 corrosion problems.

Apparently, galvanic corrosion is ocurring unabated right now on my Bravo 3. Many people commented on my photos saying it doesn't appear to be too serious at this point as long as I take measures immediately to stop it.
http://www.montanusphotography.com/bravo/

So after much research, here is my plan in order of importance. There are a million different opinions on all this, so I'm choosing the plan that seems to be the most informed. If anyone has any comments, please speak up.

1. Need sacrificial anodes. The ones on my boat right now don't appear to be correct because after 3 months in the water, they don't appear to be sacrificing. They very well could be the wrong metal. Replace with magnesium anodes.

2. Outdrive needs to be painted to cover bare metal. Green Zinc Chromate primer, Mercury Black enamel.

3. Galvanic isolation. Without this, it will render the sacrificial anodes useless when connected to shore power to prevent stray currents from exacerbating the problem. Thinking about this model: http://promariner.com/products/galvanic-isolation/prosafefs-series/

4. Mercathode. the blue model is currently installed on my boat, but I don't think it's working and/or installed correctly. Need someone to help me determine if it's functional. If not, I may install the more powerful red Mercathode.

5. Check the bonding system to see if it is functioning properly.
 
The link that guyjg posted is great. It says just about what my original post said. Your plan sounds good, are you in fresh or salt water? Really the only thing you need to do is follow the steps in guyjg's link. I guess its up for argument on how bad the drive is damaged but you are doing the corect things now and it does have life left in it (? on how much). The zinc chromate paint is a must, like you said, then the Merc. black OEM paint. I would then use an anti fowling OUTDRIVE paint (i think Merc. has a product or a recomended one)
 
robert76 said:
The link that guyjg posted is great. It says just about what my original post said. Your plan sounds good, are you in fresh or salt water? Really the only thing you need to do is follow the steps in guyjg's link. I guess its up for argument on how bad the drive is damaged but you are doing the corect things now and it does have life left in it (? on how much). The zinc chromate paint is a must, like you said, then the Merc. black OEM paint. I would then use an anti fowling OUTDRIVE paint (i think Merc. has a product or a recomended one)
Click to expand...

Robert76 and guyig, thanks for the info and advice. I appreciate it. It is in fresh water, to answer your question.
 
Is this a problem in fresh water as well as saltwater? Also, can anyone confirm if there are particular years of manufacture that that this is a problem or is it all years? Wondering if issue has been fixed by Merc.
I'm currently looking casually at a 1998 Crownline 268 cr with the BIII drive. This has me a bit spooked.
Thanks in advance for info.
 
Environment, environment, environment...you have to check where it will be moored and the condition of the Mercathode system. A boat stored out of the water is a plus; example...on a lift. Improper electric around docks is a problem for creating stray currents.
 
Pull the props, you may see this This picture is 3.5 years old. After this I bought a lift and still using same drive. It was in brackish water, and fading FAST!!!
 

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