Therefore, A6 is a ship square, all of the unknown squares on row 6 are ship squares, and all of the unknown squares on rows A, D, and F are water squares. Therefore, we know that C7, I2, and I3 are definitely ship squares. If either C1 or C3 were a water square, then the only way to fill column C would be to have a five-space ship, which is not possible. Therefore, both C1 and C3 are ship squares. If G4 were a ship square, then it would be the fourth submarine, but there would be no way to complete row G without an additional submarine.
G are ship squares.
There was the one crucial piece of information in the second paragraph of the first frame, and after that you were sailing downwind. I guess the reason I didn't solve this puzzle is that I didn't notice that it was a 9x9 grid instead of the more usual 10x10. I think I would have put in the time to solve this one if I had.