The destroyer is the ship size one step above a frigate. By default a destroyer has a larger hold and tank than a frigate, at the same speed, and a higher base structure.
The excavator, the tanker, the raider and the wayfarer are destroyers. A destroyer is one size too large for an Outpost's dock, so it docks only at a cruiser-size station, such as a Port, a Forward HQ or a combat station, or at an Anchorage.