In 1967 Waterman produced the W-11 Chevy Bird N262Y, his 11th design, as test bed for Chevrolet Corvair motor car engine. An open cockpit high wing monoplane, power was a 140hp Corvair engine. It was open frame fuselage; wings and tail from a Cessna 140.
The Chevy Bird was later fitted with floats and promptly christened Chevy Duck N262Y.
The W-11 designation wasn’t changed when it became a seaplane.
The NTSB website mentions the W-12 as N6039, an airplane that was damaged during tests in 1971 with Waterman himself on board.
There is clear mention of the W-12 as a landplane:
All Aero 