stopping drive corrosion?
 

besides using the merc anti-corrosion system and proper zincs is there anything to stop the factory paint from blistering and chipping in fresh water? are there certain paints that may work better?

If you're getting an awful lot of corrosion with the Mercathode system working and proper sacrificial anodes in place, the first thing I'd be checking for is stray current at your dock. Boat / US had a great article on it last year in their newsletter.

if you are bottom painting keep the bottom paint 1" from the drive on the transome, used the correct drive anti-fouling paint(NOT bottom paint) and if you have a bravo III they eat themselves up no matter what you do..POS !!!!

Corrrect on all accounts.
Those S/S props counteract with the Mercathode and zincs. My cruiser has S/S and I want to swap them out for Al props just for this reason.

Check for stray curent 1st. Docks are bad about this. Amazes me just how any power cords I see laying in the water. Make sure you also have a isolator if you have shorepower. Dock next to new boats. ;)

Use Magnezium in fresh water, don't tightly wind the excess of your shore power cord around steel pilings at the dock or have your neighbors do it either.

+1 on the galvanic isolator if you keep your boat pluged in or use shore power

Docks can have stray current without the power cords. Many docks are made with 6061-t6 aluminum which has excellent corrosion resistance, but if you are one side or the other on the galvanic scale (anode/cathode), will spell troubles. Another important consideration, magnitude of galvanic coupling is not just based on material properties, but surface area. For example, a steel ship with say 1000 square feet of exposed steel will need x amount of zinc to protect it. A ship with 2000 square feet sea water exposure would need 2x surface area of zinc.

Simply put, there needs to be good balance between surface area of zinc to surface area of metal to be protected. This ratio changes based on average galvanic potential of all the materials to be protected. Also, you need excellent conductivity (0.2 ohms per Interface is the aerospace requirement) amongst all the various materials to be protected by the sacrificial anode (zinc). There is a minimum current flow required, dunno the number off my head, google it.

One other thing, zincs do nothing once the boat is out of the water. Air is not a good conductor unlike water.