In terms of vessel design, there are many, many more just like those two. Very popular whalewatch/head boat design around here. If you're in boston around the Rowes Wharf area or down the cape this summer, check out the Portuguese Princess II, definite twin, with the addition of a way up there steering/spotting station on the roof of the pilothouse. The Majestic Princess and Portuguese Princess I are also similar hulls, but I'm not positive that they're identical. All formerly owned by Harbor Commuter Services, which ran the Boston-Hingham run before Boston Harbor Cruises. Once I replace my new camera that went for a swim in the mystic river, I'll post some pics.

Twins here - looking good!