The Southern Cross 31 is a  double-ender designed by Tom Gillmer, a professor of naval architecture at the US Naval Academy, and built by the C.E. Ryder Corporation of Bristol Rhode Island. The design takes influence from shapes dating back to Colin Archer’s work nearly a century earlier, and the hull in is similar the straight transomed Allied Seawind 30, an earlier Gillmer creation notable for being the first fiberglass boat to circumnavigate the globe. 

The SC31 is a full keeled sailboat with an outboard rudder and tiller. The vessle is suitable for ocean passages. The cutter rig with bowsprit has 447 sq. ft. of canvas, plenty for its displacement. Two interior layouts were offered, one with a stand up navigation station over a large locker and one with quarter-berth. The overall construction quality was of a good standard, suitably strong for offshore work. The hulls were built in fiberglass, some cored in Airex foam, while the deck and cabin house was cored in balsa.

In total over 150 boats were built between 1976 and 1987. Some were sold as hull and deck kits.