Bottom paint on stern drive

Coz

Active Member
Oct 9, 2018
443
Boat Info
2008 Sundancer 310
Engines
Merc Mag 350 DTS w/Bravo III
I know you’re supposed to leave a small gap between bottom paint and drives. How important is that if the drives have zincs and mercathode? I’m in freshwater during summer only.
 
Fresh or salt doesn’t matter. The materials in hull bottom paint will react with the aluminum and create an electric circuit that in turn will accelerate corrosion of the aluminum.

I assume your 310 is wet slipped and the drives constantly submerged. If so you should also look at coating the drives with a bottom paint for metal like Trilux. Trilux will slow down corrosion from the galvanic circuit created by the SS components and aluminum.
 
Really important to leave a gap unless the bottom paint is copper free, then it is fine.
 
Thanks guys. Maybe if I mask the area off I can scrub off the area with a toothbrush
 
Like mentioned if the bottom paint has any copper in it (most do) and thse paint is upto and touching the outdrive assembly, then your outdrive and bottom are electrically "connected". Copper is more "noble" than aluminum, so now your out drive becomes an anode to the hullbottom and galvanic corrosion will set it. Same type of reaction your outdrive anodes protect your drive from. Only now the outdrive is protecting the copper bottom paint. Probably not as dramatic as the reaction between your BIII with big SS props and the zinc or magnesium anodes, but still could cause a corrosion issue. Tape it off and clean off a gap between the bottom paint and outdrives - if nothing else you will sleep better! Plus it looks good.
 

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