Thelonius was custom-built in 1953 for a Portland, Oregon dentist who wanted a "traditional style" boat, so Ed Monk, Sr. revised a 1928 plan. Built by Admiral Marine, Lake Union, Seattle. Originally powered by a Chrysler Majestic engine plus a small "get-home" engine, both located beneath the rear cockpit. Now powered by a 150-hp Hino turbo diesel. Yellow cedar hull planking is glue-wedged, rather than caulked. Cabins, decks, transom are teak; interior details are mahogany.