The old sailor pinned a fresh grid to the wheelhouse wall each week. The flood tide came from the west, filling one column at a time until the whole flat was under. But on neap tides — the weak ones, when the moon was at quarters — the ebb pulled harder than the flood pushed. The water drained back from the western edge first, the exposed shore where the wind helped the ebb along, leaving only the deepest channel on the far eastern side. Just one column of water against the seawall. The next spring tide would fill it all again.