The Aquarius 21 is a recreational keelboat first built in 1969 by Coastal Recreation, Inc in the United States, and now out of production.
The design was also sold in slightly modified form as the Aquarius Pelican from about 1978 and, later, the Balboa 21.
Designed by Peter Barrett, the fiberglass hull has a spooned raked stem, an angled transom, a "pop-top" cabin, a transom-hung rudder controlled by a tiller and a retractable centerboard.
The boat is normally fitted with a small outboard motor for docking and maneuvering.
The design has sleeping accommodation for two people, with a double "V"-berth in the bow cabin and two quarter berths in the main cabin, under the cockpit. The galley is located on the port side just forward of the companionway ladder. The galley is equipped with a stove and a sink. The head is located under the bow cabin "V" berth, on the port side. Cabin headroom is , or with the "pop-top" open.
The design has a PHRF racing average handicap of 273 and a hull speed of .
It has a fractional sloop rig.