Why sailing warships could not rely on fixed trajectory tables

Why did gunners calculate trajectories instead of using adjustable sights and standardized range tables?

Ship motion, hull differences, and uneven gun-deck geometry made fixed corrections much less reliable at sea than ashore.

Trajectory tables could help, and later sailing warships sometimes used them, but every hull and firing position behaved differently while the ship moved through six axes at sea. Curved gun decks also changed the local geometry from one weapon position to another, so a correction calculated for one gun could not simply be transferred across the battery. Later hulls became longer, broader, and somewhat more level, making coordinated gunnery more practical. At sea, repeatable shore calculations gave way to continual judgment aboard a moving ship.