Solution to Evan Birnholz’s Oct. 24 Post Magazine crossword, “Sea Changes”

I gave myself two constraints while building this puzzle. First, the C’s in the theme answers could be the only C’s in the whole grid. Since the name of the game is “change C’s to other letters,” then I thought it would be odd to have stray C’s elsewhere that don’t change. Second, I wanted the crossing Down answers to become real words when you change the C’s to the correct meta letters. CAIN at 24D, when you change the C to an M, becomes MAIN; SEC at 13D, when you change the C to an E, becomes SEE; and so on. Both of those constraints gave me several headaches, but fortunately not so many that I had to abandon the plan.