Differential zinc corrosion

Hydraulicjump

Well-known member
Joined
Feb 10, 2011
Messages
646
Fluid Motion Model
C-30 CB
Hull Identification Number
FMLT2911F415
Non-Fluid Motion Model
Necky Looksha VII, Liquidlogic Remix, Jackson 4Fun
Vessel Name
La Barka (2015)
Here's a mystery that smart Tugnuts can solve, I bet. I hauled the boat to get the electrical gremlins fixed and noticed very different rates of corrosion of the zincs. Most notable are the trim tab zincs. The port side trim tab zinc is corroding much faster than the starboard side. And here is the catch: the zinc disk on top of the port side trim tab is corroding much faster than the zinc on the underside.

I am in a very "hot" marina and have simply disconnected from shorepower, relying on the solar panels to do the work of keeping batteries topped up. The port side gets most of the sun (and abundant algae growth on the trim tab). I have a grouper over the side, near the rudder.

Does sunlight and/or high rates of photosynthesis/respiration (daytime rise in pH, nighttime decrease in pH) accelerate corrosion? Given the tides in my marina, I doubt that local pH changes would affect this, but not sure.

The alternative hypothesis, to be tested next time I change zincs (moving to aluminum), is differential product quality.

Just an observation.

Jeff
 
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