Where the Hull Rests the Surface
Puzzle 4 of National Crossword Day Hard Pack
Question is: Where the Hull Rests the Surface
and the answer is: WATERLINE
Word Meaning:
WATERLINE — (nautical) A line formed by the surface of the water on the hull of a ship when she is afloat; any of a series of short lines marked on the hull to show where the waterline would be under different loadings
Definitions from Wiktionary.