Ship at Full Length

Easy Used by Smart Hint

This ship run is already as long as the longest ship still unplaced — it can't grow, so the cells at its ends are water.

Ship segment
Water
Cells that establish the pattern
Where the conclusion lands

How it works

This two-cell run is already as long as the longest ship still unplaced anywhere in the fleet — say both bigger ships are already found.
Growing it by even one cell would make it a longer ship than anything left to place.
Seal it: every open cell touching the run is water.