Zincs and Bravo III Outdrive Corrosion

wish2fish

wish2fish

Active Member
Dec 19, 2006
4,278
Locust Creek, Ohio River mm 433
Boat Info
2003 220BR
Engines
5.0 MPI
My 2003 Bravo III outdrive is showing some signs of corrosion. The boat is kept on a solar charged 12v hydraulic lift. The only time the outdrive is is the water is when I am using it. Freshwater use only, Ohio River.

First, I have included a picture of 3 of the zincs. The 2 on the other side look the same as the hydraulic and cavitation plate zincs. There isn't a prop zinc. Are the zincs in good shape. Do I need to replace?

Is there something else I should be looking at?







Here are the pictures showing the corrosion on the outdrive. planning on sanding and repainting before launching.







Outdrive fluid drain
 
That is significant corrosion for a dry racked boat. I keep mine in the water 6 months a year and it looks near perfect. First off, if freshwater then magnesium anodes. Yours do not look too bad but rule of thumb is if they appear 50% then change them. Second, check your Mercathode system for power and for activity readings. Here is a simple test:

Check mercathode power on two center screws - 12vdc
Mercathode System Testing
When the boat is in the water, disconnect the orange wire that comes from the anode at the mercathode controller. Set the digital reader to show milliamps. Connect the black meter lead to the terminal on the controller. Connect the red meter lead to the end of orange wire. If using the blue or black Mercathode controller, the reading should be 25 or less milliamps, to as much as 200 milliamps in saltwater areas. If using the red Mercathode controller, the readings should be less than 25 milliamps in fresh water areas to as high as 400 milliamps in saltwater areas.

lastly check that all the grounding wires are connected on the drive. Again I would expect a dry stored boat to be perfect.
 
I second the wires...I had several broken and missing wires.
A new continuity kit may be in order...apx $20-$25 bucks.

Jeff
 
From the pictures, it doesn't look like the anodes are actually wearing away? It looks like there is a buildup ON the anodes. Don't rush to put Mg anodes on there - check with others in your area that have a similar setup and have GOOD results. Mg can sometimes OVER protect in fresh water. You may find that Al anodes will work better. There's no "hard and fast" rule that says one or the other - local experience trumps anything written on the internet. Performance Metals makes a VERY good Al anodes - better than OEM, in my opinion.

Good advice above... check wires, also check that your Mercathode is working.

You can repaint any bare spots with Zinc Chromate (or phoshphate) and then black paint - just use the same brand primer and topcoat. Merc has a grey-colored primer which also works well - but use Merc's topcoat then, as well.
 
It it possible part of your drive is partially in the water while it is on the lift? Most of your corrosion is around the bearing carrier, which was a bad spot on the early Bravo III;s (before the extra anodes were added). If your props and lower half are in the water and the upper part is not, there is no protection because your anodes are out of the water and you don't have a prop shaft anode. How much time does the boat spend in the water at a time? Your anodes are pretty depleted - they look like the magnesium anodes would on my old Bravo III after a season in freshwater. I had corrosion problems with mine until I switched to magnesium anodes - after that corrosion was not really an issue - I had the new drives with the additional anodes. If your boat is dry stored and the drive is completely out of the water, corrosion is just not a factor.

While a lot of corrosion for a dry stored boat, it really is not that bad, it can be cleaned up - you need to sand and clean up all the corrosion, the prime with zinc chromate primer and paint. The bearing carrier has a zinc chromate coating. I don't know the exact coating used as OEM, but I have heard of people just priming and painting those also. I would consider adding a prop shaft anode also. Keeping a good coat of paint on the drive is key to fighting corrosion, once the finish is compromized, usually along an edge, and the aluminum is exposed, the corrosion starts - slowly but surely, just like rust under the paint on a car.
 
I was just thinking about whether I leave the prop in the water while I'm using the boat (during the weekend). It is very possible. I usually lift the fiberglass out of the water 6-8 inches. If drive still in down position it would be in the water. I'm going to make sure it is out of the water now.

I was looking at the prop shaft. I don't think there is a place to screw the prop anode on there.


I got the quicksilver phantom black and marPro zinc chromate primer to redo the drive.
 
If the lower part is left in the water, that totally explains the situation. I looked at the anodes again and it still appears that they are not worn at all. If they're the Merc brand, they would be Al and I would still use them. But, I would brush them off with a wire brush to get that crud off, though.
 
I believe Mercruiser came out with a enhanced or 2nd gen Bravo 3 around 2004 that included a 2nd cavitation anode as well as the prop anode.
But like Bill said...there is a kit for the prop on older models.

Jeff
 
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And I would still check to make sure you have all of the continuity wires on the outdrive.
There should be one from the engine ground stud to transom, one on the steering lever to transom, transom assembly to inner transom plate, gimbal ring to gimbal housing, gimbal ring to bell housing and one from each trim cylinder to the gimbal housing.
There is also a position ground plate on the port side middle drive nut that gets screwed to the drive unit.
And lastly there should be lock washers between the connector and each nut on the hydraulic connector the lines attach to.

The continuity kit part# is 99940A 2 if you need it.

Jeff
 
Looking at the photos some more, they look like aluminum anodes. I maintain to check the mercathode and ground straps. If all in tact, I bet you need magnesium.
Here in PA, freshwater, aluminum is too noble a metal and magnesium is a must.
 
paulswagelock said:
Here in PA, freshwater, aluminum is too noble a metal and magnesium is a must.
Click to expand...

No, there is no way to make a blanket statement like that. We've found that, for example, at Lake Wallenpaupack, that most of our customers fair much better with Aluminum anodes. It really all comes to the particular "fresh" water. That's not to say that Mg can't work at Paupack, but Al seems to work better for most. The Perf Metals... even better.
 
I second that. I'm on the Delaware River and my drive was getting eaten badly with magnesium. Switching to aluminum made a big improvement, along with adding some wires from the continuity kit that were missing.
 
I went from MG to the Performance Metals AL and a very positive difference. Primed and painted last spring, installed the new anodes, and OD looks as good a year later.

I believe their AL is called Navalloy. I won't go back.

Bennett
 
Not to jack this thread but it has me thinking also...

My boat is in south Florida saltwater.. I just replaced the zincs and here what they looked like after 30 hours in the water. The creamy residue could be wiped off but it was a little sticky. Looks similar to the OP's zincs. Not sure if that was normal either.


6Sv7Qtsl.jpg
 
^^^ What type of bottom paint do you have on the hull? Your paint connects right to the lower unit. Hopefully you have copper free paint.
 
paulswagelock said:
^^^ What type of bottom paint do you have on the hull? Your paint connects right to the lower unit. Hopefully you have copper free paint.
Click to expand...

The shop used Interlux ablative paint but I am not sure what exact version they used. Guess I should give them a ring.
 
I believe they have one called Micron CF (copper free). If copper based paint, there needs to be a 1" gap from the paint to any metal surface. Without it, there is the ability for current to flow between the two surfaces providing the ability for damage.
 
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