The RK 21 is an American trailerable sailboat that was designed by Peter Barrett as a cruiser and first built in 1972.

The design was built by RK Industries, a subsidiary of Coastal Recreation, Inc, in the United States. It was built starting in 1972, but it is now out of production.

The RK 21 is a recreational keelboat, built predominantly of fiberglass. It has a masthead sloop rig; a spooned, raked stem; a slightly angled transom; a transom-hung rudder controlled by a tiller and a swing keel. The design displaces 2,000 lb (907 kg) and carries 665 lb (302 kg) of ballast.

The boat has a draft of 4.58 ft (1.40 m) with the swing keel extended and 12 in (30 cm) with it retracted, allowing operation in shallow water, beaching or ground transportation on a trailer. The boat is normally fitted with a small outboard motor for docking and maneuvering.

The design has sleeping accommodation for two people, with two straight settee berths in the main cabin.