SAN DIEGO — A spring storm had retreated inland during the night, leaving a canopy of unbroken clouds over Mission Bay. About 20 engineering students and others gathered in the morning chill to launch a cockeyed-looking vessel, mechanical guts fully visible, into the still water.

The contraption’s hull, cannibalized from a 16-foot, decades-old catamaran, supported a conveyor belt, motor and array of batteries the size of a picnic cooler. Solar panels were mounted like an awning atop the aluminum frame. Its creators had relied on off-the-shelf materials during construction and christened the result FRED — an endearing acronym for floating robot for eliminating debris.