Doubt that crevice corrosion
would be a problem with a center board. Crevice corrosion needs an oxygen free environment/stagnant water
like where a chainplate passes through the deck
or a shaft through the log. That's not the case with a centerboard
floating free in the well where it gets regularly flushed with new water
For something that will undoubtedly be covered with anti fouling paint
, 304 should work fine. Going to be one heavy board at one inch thick.