The Waterman company was bought by the Arrow company in 1917. Arrow continued to offer "Waterman" rowboat motors. See Arrow for motors produced after the buy out.

http://www.angelfire.com/mi4/hartsmith/thesnows.html
Click on the examples below to view photo albums.
Note the vocabulary used by the 1907 Waterman ad above. They have no name for the new type of motor that is detachable, still calling it a marine engine (which designates an inboard). A very similar, but not identical, 1908 ad is below the PORTO ad.

Below: 1914
Two full page ads for the Porto from 1914. CLICK IMAGE

Waterman C16
#16173
I have not had time to sort many odds and ends...but here they are untill I get to posting them.