Why were ships of the line too large and expensive for chasing merchant ships?

Ships of the line were designed as heavy, powerful "mobile fortresses" intended to fight in coordinated columnar formations, where their primary value lay in their ability to endure punishment and deliver massive broadside firepower against other heavy warships. Because these vessels were large, cumbersome, and expensive to operate, they were ill-suited for the tasks of scouting, patrolling, or chasing down merchant ships.123

Instead, navies utilized frigates and smaller vessels for these duties. Frigates were specifically developed to be faster and more maneuverable than ships of the line, making them ideal for commerce raiding, escorting, and independent patrol missions. While a ship of the line required a massive crew—often 600 to 800 men—and was built to anchor a battle line, the frigate provided the necessary speed and efficiency to engage or pursue smaller, more elusive targets on the fringes of the fleet.312