2003 Bravo III corrosion / rotting?

[charlg]

Am I in trouble here? All of a sudden, I'm noticing what looks like corrosion. I am slipped in fresh water and the boat comes out of the water frequently to take trips. I've never noticed this until a month ago. Since then, it seems to be geting worse. I replaced the anodes at the beginning of the season.

If it is corrosion, what can I do to stop any further damage? Sand / paint?

I know there is an inherent problem with the BIII and corrosion. Do I have one of the problem years? Should I contact Merc?

Thank you.

 

[charlg]

Sorry, forgot the pics.

 

[Dave S]

You don't have one of the "problem years" but it could be your Mercathode is not working properly, or you have a problem with the bonding system, or you have the wrong anodes. In fresh water you should be using Magnesium Anodes.

And yes that corrosion looks like electrolysis. You can sand and repaint but until you figure out what's wrong, the corrosion will come back. Fopr further information, you can search the board. There are several extensive postings on B3 corrosion issues and solutions such as this one. Just search using the term "Mercathode".

http://clubsearay.com/forum/showthread.php?t=758&highlight=mercathode

 

[techmitch]

once the paint comes off or is worn/scraped off corrison can get out of hand very quickly, so get the upper hand on it a.s.a.p. here are some links i hope they help.

http://www.outdriveshop.com/galvanic_corrosion.html

http://mercstuff.com/bravo3corrosion.htm

 

[mwph]

Dang! My first real chance to offer some help and techmitch beats me to it! The site he offers is a good one. I will add this...your comment "all of the sudden" may be a concern. If you scrapped it up that is one thing. If the problem continues after you paint it then you, or your slip neighbor, may have some electrical issues to deal with.

Mitch.......Do you have bilge water in your veins?

 

[charlg]

Sounds like I should keep her out of the water until I get a handle on this. I hope it's not too late. Thanks for the links, I will read up on the problem.

BTW. I put aluminum anodes on the drive. I slip in fresh water, but take trips in the salt.

 

[Fishnut]

Too bad you are out of warranty. I have one that is showing signs of corrosion after 1 1/2 years. My merc is working fine, I wash the outdrive all the time, some of them are okay and some of them rust like a Detroit junker.

 

[Nehalennia]

WARNING WARNING WARNING.
Start trailering now until you can iron out what's wrong. Yes, you're in trouble if you don't. The next guy to buy your boat will ding you hard if he goes to buy your boat and it looks like it's been rotting off the boat.

Here's what mine looked like before the previous owner paid to replace it.

You don't want to have to do that and more importantly you want to go boating and enjoy your boat, trouble free.
Does your prop shaft had the anode on it? If not get it. I've heard that they are a tremendous help against electrolysis.

Best of Luck. Sorry to see it.

 

[280 SeaRay]

Wow. I hate to see pictures like this. Good luck with the fix.

 

[charlg]

OK. I've read for hours on the subject of mercathodes. But, I couldn't find the answers to a couple of questions.

1) How do I check to see if the mercathode is working properly?

2) Did I put the correct anodes on? I used aluminum (boat in both fresh and salt).

3) Is there a good link for repainting the outdrive? I saw Dave S' beautiful paint job...but no details.

I am going to trailer the rest of the year.

Thanks for the help.

 

[Dave S]

OK. I've read for hours on the subject of mercathodes. But, I couldn't find the answers to a couple of questions.

1) How do I check to see if the mercathode is working properly?

2) Did I put the correct anodes on? I used aluminum (boat in both fresh and salt).

3) Is there a good link for repainting the outdrive? I saw Dave S' beautiful paint job...but no details.

I am going to trailer the rest of the year.

Thanks for the help.

For some good information on the Mercathode and how it operates and how to test it, take a look at this. http://www.mercstuff.com/bravo3corrosion.htm

As far as painting goes, start by sanding the corrosion down as much as possible. I use a dremel tool with a paddle wheel sanding attachment that works real well, I also hand sand everything afterwards then mask and paint. I recommend you use Mercury's primer on the outdrive followed by several coats of Mercury Phantom Black. I have tried Zinc Chromate primer before and I don't recommend it. I think the Zinc actually encourages electrolysis and my experience after painting mine three times is the Mercury primer works best.

 

[280 SeaRay]

The service manual for the BIII will also have the procedure to check the Mercathode system.

 

[67vetteal]

I've posted for years on this problem particularly on the former board. We all know the reason for your problem and yet most B III owners do not take the necessary steps to minimize Electronic Galvanic Corrosion. Stray current, whether a local environmental problem or the guy next to you who pumps Current into the water, plays Havoc on our drives. So, how do I save myself from costly repairs? Rap that Rascal! I paint my B III with a heavy coat of Imron, which is a two part Epoxy coating manufactured by Dupont. This prevents outer surfaces from conducting, (attracting stray Positive), current. Then My Propellers were Powder Coated using the appropriate Base coating and Black final coating provided by Dupont specifically for our Stainless Steel Props. Now I have very little exposed unprotected bare metal to attract current. All boats have a "Grounding system". Bigger boats use a Grounding Bar which provides a "Common" ground for all of the boats systems. These systems provide a safe haven for the left over current to exit our boats electrical systems. (This is why we periodically need to clean our grounds.) When a Vessel suffers from excessive corrosion on the drive it is wise to place a Sacrificial Anode over the side which is connected to the Negative Battery Terminal via a sturdy Copper wire. In fresh water our Aluminum Casings need a more Noble metal than the drives Aluminum, keep this in mind when selecting your Anodes. Al W.

 

[Presentation]

.......2) Did I put the correct anodes on? I used aluminum (boat in both fresh and salt).......

I agree with the advice given. I’m going to focus my answer on your question about anodes.

I recommend you use magnesium anodes.

Let me please explain this.

First, you say you boat in fresh and salt water. From reading your post it sounds like most of the time you keep your boat in fresh water with occasional trips to salt water but you are not in salt water for long.

Will magnesium anodes work in salt water? Absolutely yes. So why don’t all salt water boaters use magnesium anodes? Because in salt water they ware out relatively fast. But if you go into salt water, boat then come back out, not slip in salt water, you are protected and the additional wear to your anodes is a smaller price to pay then the cost of a new outdrive.

Magnesium will last 1/4th as long as zind and 1/5th as long as aluminum in salt water.*

Anode Alloy Voltage(1) Density Energy Capacity Relative Life to Zinc
Zinc (Mil-A-18001K) -1050mV 0.258 lbs/in3 368 A-h/lb 100%
Aluminum (Mil-A-24779SH) -1100mV 0.105 lbs/in3 1108 A-h/lb 120%
Magnesium (Mil-A-21412) -1600 mV 0.063 lbs/in3 500 A-h/lb 25%

So aluminum anodes will last longest but magnesium anodes will be most active however will need to be replaced more often.

But….you are having a issue. Its time to step it up. Go with magnesium. Even at a frequency of 5x the rate of aluminum anode wear, once the drive is painted as advised above you should get at least 6 months life out of a set of anodes before they are at ½ mass, meaning they need to be replaced. This assumes you are mostly in fresh water and do not slip in salt or brackish water.


Additionally, I can not tell from your photos if you have the propeller anode. The addition of the propeller anode was mid year 2003 so you may or may not have this from the factory.


If you do not have this additional anode, you can buy a kit that allows you to add this additional anode. Basically, the kit is a new prop nut that allows you to screw the anode to the nut.

http://www.boatzincs.com/mercruiser-magnesium.html

At issue is all that stainless steel from two propellers. Stainless steel is more noble then the aluminum drive. This is why you are seeing the corrosion close to the propellers. The prop anode puts the sacrificial magnesium anodes where you need it most.


When it comes to my anode recommendation when it comes to a Bravo III drive that is having a corrosion issue and is mostly in fresh water I advise you go with magnesium anodes, make sure you have the propeller anode and keep an watchful eye out for anode ware as you will need to replace magnesium anodes more frequently then aluminum anodes. (5x as frequent)

 

[Jim240]

Looking at your pictures, you have some dominant horizontal lines on the skeg... you didn't run through some sand recently? Maybe some muck? To me it looks more like paint wear than corrosion. Notice on Todd's drive how pattern seems to grow from exposed ends.

Nevertheless, once the underlying aluminum is exposed, it needs to be painted or it will corrode. Your aluminum anodes need to be occasionally brushed with a wire brush to take off the clad layer (aluminum oxide). Anodes will begin to corrode, build a stable oxide layer on the outside and then loose effectiveness. The guy who taught me to do this was actually showing me the drive Todd was having replaced as the example of why to do this.

As for the Mercathod, my local mechanics tell me not to put too much stock in the system. If there's any current (water flow, not electrons) in the area, it tends to cause the protective field to drift, at least that was their claim. It seems if you really want to protect your boat, one of those tubs that you can drive your boat in and then close up, so the water around your boat is trapped, is probably the best thing you can do, sort of dry stacking.

 

[charlg]

I agree with the advice given. I’m going to focus my answer on your question about anodes.

I recommend you use magnesium anodes.

Let me please explain this.

First, you say you boat in fresh and salt water. From reading your post it sounds like most of the time you keep your boat in fresh water with occasional trips to salt water but you are not in salt water for long.

Will magnesium anodes work in salt water? Absolutely yes. So why don’t all salt water boaters use magnesium anodes? Because in salt water they ware out relatively fast. But if you go into salt water, boat then come back out, not slip in salt water, you are protected and the additional wear to your anodes is a smaller price to pay then the cost of a new outdrive.

Magnesium will last 1/4th as long as zind and 1/5th as long as aluminum in salt water.*

Anode Alloy Voltage(1) Density Energy Capacity Relative Life to Zinc
Zinc (Mil-A-18001K) -1050mV 0.258 lbs/in3 368 A-h/lb 100%
Aluminum (Mil-A-24779SH) -1100mV 0.105 lbs/in3 1108 A-h/lb 120%
Magnesium (Mil-A-21412) -1600 mV 0.063 lbs/in3 500 A-h/lb 25%

So aluminum anodes will last longest but magnesium anodes will be most active however will need to be replaced more often.

But….you are having a issue. Its time to step it up. Go with magnesium. Even at a frequency of 5x the rate of aluminum anode wear, once the drive is painted as advised above you should get at least 6 months life out of a set of anodes before they are at ½ mass, meaning they need to be replaced. This assumes you are mostly in fresh water and do not slip in salt or brackish water.


Additionally, I can not tell from your photos if you have the propeller anode. The addition of the propeller anode was mid year 2003 so you may or may not have this from the factory.


If you do not have this additional anode, you can buy a kit that allows you to add this additional anode. Basically, the kit is a new prop nut that allows you to screw the anode to the nut.

http://www.boatzincs.com/mercruiser-magnesium.html

At issue is all that stainless steel from two propellers. Stainless steel is more noble then the aluminum drive. This is why you are seeing the corrosion close to the propellers. The prop anode puts the sacrificial magnesium anodes where you need it most.


When it comes to my anode recommendation when it comes to a Bravo III drive that is having a corrosion issue and is mostly in fresh water I advise you go with magnesium anodes, make sure you have the propeller anode and keep an watchful eye out for anode ware as you will need to replace magnesium anodes more frequently then aluminum anodes. (5x as frequent)

I'll go with the magnesium anodes. Does most everyone use boatzincs.com? They are local to me, and I bought the last set of anodes from them. Or, are Merc anodes better?

 

[charlg]

Well I filed, sanded, primed, and painted. It came out OK for my first attempt.

Boatzincs.com recommended that I stay with the aluminum anodes and buy a magnesium grouper. Anyone use one of these?

 

[douglee25]

This? I've never used one. I wonder how effective they are?

http://www.boatzincs.com/grouper-specs3.html

Doug

 

[Nehalennia]

Charlg,
That looks much better
Wet sand it, throw another coat or two of paint on, wet sand one more time, then polish and she'll be looking pretty good.

The Grouper idea looks like a good one.
From that Site.

Q) I dock my boat in freshwater but plan to spend some time with it this summer on the ocean. Which anodes should I use, magnesium or aluminum?

A) Never use magnesium anodes on outdrives that will operate in saltwater. They are too strong and can peel paint and damage the metal housing of the outdrive. Instead, install aluminum anodes on your outdrive for the season, and when at your freshwater dock suspend a magnesium Grouper anode overboard within a couple feet of the outdrive(s). This provides the corrosion protection benefits of both types of anodes


Best of luck