Need Help- Serious Electrolysis Problem

[Rock Hall]

I have a 1989 220DA. Running 2 batteries. Mercathode unit, that I know little about. Salt Water slip 5 months a year. When I bought this boat, it had some electrolysis damage on the drive. Not real bad. After the first Summer in the water, it didnt seem to get any worse. Winter of 07 I stripped and smoothed out the housing and repainted. Last fall when I pulled the boat I had major Electrolysis damage to the Prop and tubes. Has the tubes rebuilt and new end caps. My prop literally had holes clear through is and it looked like I did nothing but run it through rocks. Also lost half the skeg. I rarely touch the bottom with this boat. And it is mostly a soft bottom when I do.
Talked to the Searay dealer. He says cant be my boat because Searays have an isolator. Must be a neighbor or the docks. So I go to the marina. They want to use their new test equipment, charge me $100 and test my boat.
My boat has been in the slip for 4 weeks. I've had shore power hooked up a maximun of 4 hrs during those 4 weeks. I always turn my batteries off when I leave.
I took a look at the prop today(brand new Black Max). The edges are getting rough and the flange in the tail is even getting chewed up. It looks to me like I have electrolysis again.
I have all new neighbors within 60 ft of me. None of the boats anywhere near me were there last year. I asked the Manager of the marina to check the dock wiring. He said he would, have not heard back. I have no zincs on this boat, but am planning to put what I can do while in the water on tomorrow.
So I'm looking for a lesson in electrolysis from one of you experts. What I used to know, I've forgotten. I'd like to avoid the $600 worth of damaged parts I had to replace this year.
Thanks in advance for the help.
Mark

Additional info: I was reading some of the other posts and it seems that a charger can be a factor. My boat has a Guest 2-bank 12 amp charger that went totally dead on me at the beginning of the season last year. It is still hooked up and I plan to replace it within the next couple of weeks. It lights up, but puts out nothing. Can this cause the problem?

 

[Hampton]

I think you answered the question yourself "No Zincs." Metal in salt water will corode. You need to be proactive to ensure the expensive parts aren't the ones dissolving. Make sure all of your grounds are making a good connections - no corrosion. Even so, until you get protective zincs, you will not stop the process.

 

[boatmailster]

Zincs, zincs, zincs especially on bravo drives - small price to protect your investment.
If bottom painted - paint on transom shouldn't touch bell housing - new bottom paints are conductive and speeding corrosion process.

 

[Morpheus]

Wow no zincs? That's gotta be it you should see my prop hub zinc just after 2 weeks in the water, looks like swisscheese.

 

[Rock Hall]

Tried to buy some zincs yesterday at West Marine. Unfortunately, they had no one there that knew anything about them and ended up with the wrong ones. Went to my marina and put an order in the the right ones to be ready to pick up next Sat when I go back down to the boat. I'm starting with the Prop Nut Zinc and the 2 for the trim tubes. I can get to those from the swim platform.
I also need to test the mercathode system. My guess is it is not working.
Thanks for all the tips.

 

[Hampton]

I may be wrong, but I don't think the Mercathode system can work without zincs.