Why frigate, sloop, and brig labels can overlap

Can frigates, sloops, and brigs legitimately be grouped together?

Sometimes: depending on period and type, a large brig or sloop and a small frigate could fall into a closely related category.

Rig, size, date, and local usage could blur the boundaries among frigates, sloops, and brigs. The labels can therefore be grouped in a limited context without treating them as permanent equivalents. A large brig or sloop could occupy much the same operational space as a small frigate. Classification still depends on the specific vessel and period, so the overlap should not erase real distinctions in other eras.