corrosion on skeg of b-3 outdrive

C

chazaroo

New Member
Dec 4, 2006
415
Florida
Boat Info
1996 Sundancer 250
Engines
single 5.7 w Bravo III
Had our 250 out for detail and service and noticed corrosion on the lower unit of the outdrive. (Boat is docked at our house in South Florida in Brackish water.)We've had a diver coming once a month to clean and check zincs but he must not have been doing a very good job. Anyway, the marina suggested a grouper anode that should be connected to the negative pole of one of the batteries and left overboard to protect the drive. I went on line and found one for sale but the directions said "Do not connect to negative pole of battery." I bought the anode today at at a local store but have no idea where to hook it up. I want to get it going before I destroy the outdrive. Anybody got a clue as to what I should do?

-chazaroo
 
Be thankful that's all the corrosion you have. I keep mine dry stored and it has corroded over 30% of the surface. If your warranty isn't out make a claim and get a new one.
 
Clean and repaint the skeg then check or have checked the potential around the boat with a multimeter and test probe for the proper potential. It may be something locally that is overwhelming your Mercathode system. Do a complete check of the entire bonding system as well. I think it's great that you only have skeg corrosion but definitely take care of it so it doesn't progress to the carrier or worse. You should be able to control this. I hope the skeg is not beyond refinishing. I am not sure but did they install a second controller for your Mercathode? or is there just one?I Think it may be standard now that a second controller is installed.
 
Pretty sure I read that these should be connected somewhere in the bonding system, not directly to the battery, but check that out on one of these 2 sites ...

www.mercstuff.com or www.outdriveshop.com

(I'm going to verify this because Im interested in the grouper too).

As a side note - since its only the skeg, any chance it was painted with the wrong paint?
 
Thanks all for suggestions. Maybe having somebody test is a good idea. Marina said hook grouper anode to battery, not sure I trust them. Skeg was cleaned and repainted during service. zincs were also replaced. Still trying to figure out the Grouper Anode issue as to where it should be hooked up. The end is a battery type clip. as for the merthacode controller, I don't know. How do I check that?
 
How bad is it? Considering the fact the this is a twelve year old outdrive, some would be expected especially a BIII of that vintage in your area (unless it's not original).
 
a common belief is that the grouper style annode will work anywhere. The essential criterion is that it is in direct contact will the metal being protected. through a wire in this case a clip or to a vessels bonding system all those green wires connected to everything metal in contact with water.The test for a mercathode annode is an in the water test, utilizing a special silver/silver chloride test probe and a multimeter. The probe reads electrical potential around the metal underwater that you are testing and the results can indicate the metal is sufficiently protected with annodes or sacrificial metal. I suggest you type in Mercathode on the internet and read everything as it really is too much to go into here,plus there are many good pictures to refer to for a better understanding of what takes place or what should be taking place around your metals. The mercathode weak link as with any electrical device is that it needs a constant supply of 12v power to provide the repulsive electrical field around your drives. When you loose battery power it stops working. Check the controller on the engine for 12v and that the fuse is intact.These systems can also fail over time and must be replaced.If you feel uncomfortable doing this yourself a qualified tech should be used ,they will also have the digital meter and the test probe$100-$200 to do the testing .With a proper bonding system and sufficient annodes you should be able to control metal loss,. The technician will also be able to determine if there is a stray current around you vessel causing an electrolysis of metals ,again the metals bonded to enough sacrificial annode will counteract this.On my 310 sundancer The wire is connected directly to a large plate annode on my hull for this very purpose it is designed to bring the valuable metal to the same potential and let the zinc shed it's electrons instead of your drives.Remember that the key here is the electrical connection of the grouper to the drive.
 
dpvandy01 said:
How bad is it? Considering the fact the this is a twelve year old outdrive, some would be expected especially a BIII of that vintage in your area (unless it's not original).
Click to expand...
I wish I would have done more research on the BIII before buying a new boat with one. I had a BI on my last boat and sold it at 12 years old and 500hrs. There was not a spec of corrosion on the drive. One year of service on my new BIII and it looked like I had thrown a bag of chaulk dust on it. Only time will tell it's durability (with proper service) but so far this is all I read about is recurrent corrosion.:smt089
 
dpvandy01 said:
How bad is it? Considering the fact the this is a twelve year old outdrive, some would be expected especially a BIII of that vintage in your area (unless it's not original).
Click to expand...
It's an older boat to be sure but we got it three years ago and unitl then it had been dry stored at the marina and only had 150hours on it. Now, after three years at our dock, the skeg has lost about two inches of the bottom point and the forward edge has some rough edges.
 
white glove said:
a common belief is that the grouper style annode will work anywhere. The essential criterion is that it is in direct contact will the metal being protected. through a wire in this case a clip or to a vessels bonding system all those green wires connected to everything metal in contact with water.The test for a mercathode annode is an in the water test, utilizing a special silver/silver chloride test probe and a multimeter. The probe reads electrical potential around the metal underwater that you are testing and the results can indicate the metal is sufficiently protected with annodes or sacrificial metal. I suggest you type in Mercathode on the internet and read everything as it really is too much to go into here,plus there are many good pictures to refer to for a better understanding of what takes place or what should be taking place around your metals. The mercathode weak link as with any electrical device is that it needs a constant supply of 12v power to provide the repulsive electrical field around your drives. When you loose battery power it stops working. Check the controller on the engine for 12v and that the fuse is intact.These systems can also fail over time and must be replaced.If you feel uncomfortable doing this yourself a qualified tech should be used ,they will also have the digital meter and the test probe$100-$200 to do the testing .With a proper bonding system and sufficient annodes you should be able to control metal loss,. The technician will also be able to determine if there is a stray current around you vessel causing an electrolysis of metals ,again the metals bonded to enough sacrificial annode will counteract this.On my 310 sundancer The wire is connected directly to a large plate annode on my hull for this very purpose it is designed to bring the valuable metal to the same potential and let the zinc shed it's electrons instead of your drives.Remember that the key here is the electrical connection of the grouper to the drive.
Click to expand...

Thanks! This job is a little above my pay grade but I'll check around and find somebody.
 
I think the key word here is with proper service. If it weren't for the superb performance I hear about ,the continuing upkeep would be hardly worth it. I replaced a pair of lower units for a customer who had lost so much material around his carriers that they could no longer be held in. This was obviously a case of neglect as I told him and with the right care could have been avoided. One interesting thing did become evident when I installed the new lower halfs ,and it was that the cavitation plate now contained two trim tab style annodes instead of one .This is clearly an attempt by Merc to counteract corrosion , this along with the prop nut annode and all the others now protect better than the previous model. The problem lies in the failure of perhaps one part of the system resulting in catastrophic damage in a short time period. I pulled a guy out for trim ram failure to find the daisy chain wires had been severed between his trim rams and the gimble ring. The trim rams corroded so bad around the hydraulic line fittings that they blew the lines off. I guess the key is to keep checking often enough to make sure all this stuff is working . I am told from customers that I sound like a broken record, except from the guy that I had handed a $15,000.00 invoice for new trim rams and lower halfs. With this drive system and that huge chunk of stainless attatched to it the only fix is pain in the butt preventive maintenance.
 
Prop nut annode? I know I don't have a zinc on the shaft. Maybe that's my problem?
 
You might want to go to boat zincs.com try this link to the B3 anodes. http://www.boatzincs.com/mercruiser-aluminum.html

I don't know for sure but I heard there was a kit for older B3's to put the prop nut in place. I have seen very little corrosion over the past 5 years. I do keep my boat trailers and the longest it has ever sat in the water was a week at a time on vacation. Cleaning, sanding and painting each year is a must on a B3 Drive. No Exceptions. Best of luck and Merry Christmas. :grin:
 
My dad had a bravo III with the wrong anodes on 2000 and the drive looked terrible after the first season. He had the drive redone and installed the right anodes and corrosion stopped. His new drives on his current boat have looked fine after 5 seasons - but he changes the anodes annually.
 
Wow, another BIII issue. Like many I wish I had researched more before we purchased our 1995 290DA. I was worried about the pitting that was occuring before last season and had her pulled, blasted and painted by the marina. I have no idea how or who to call about the mercathode system, but hope new paint, and new anodes, including the large prop anode will at least slow the electrolosis. There are several folks on our freshwater lake that have issues with this drive. I love the perfomance, but the electrolisis issues are unacceptable from a mercruiser product in my opinion. BTW, none of the volvo's seem to have any issues. Good luck!
 
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