Complex sentence: Stevens's design contributions to the recreational boating industry included collaborations with Outboard Marine Corp. to style the Evinrude Lark and Johnson Javelin outboard motor series as well as the Evinrude Lark concept boat, eventually produced as the Cadillac Sea Lark.
Split into simpler sentences: Stevens's design contributions to the recreational boating industry included collaborations with Outboard Marine Corp. to style the Evinrude Lark and Johnson Javelin outboard motor series. He also designed the Evinrude Lark concept boat, eventually produced as the Cadillac Sea Lark.