Vireo14 is a 14' version of the original 12' Vireo which was quite popular with all of its builders. In this case the extra length comes from a straight "stretch" of the original design. By that I mean that the same cross sections were used but now spaced 14" apart instead of 12". Another way to lengthen a boat is to add a straight "plug" in the center as is sometimes done to even completed boats and full size ships. I doubt if the stretch has any advantages over the plug except maybe in looks. Even there a short plug is hardly noticable, for example in the case of where I put a 30" plug in my Toto canoe to make Larsboat.
The extra length usually gives a bit more speed for the same power in a low powered boat, at least until windage gets to be a big factor. And in the case of Vireo it means about 110 pounds more capacity. The original 12' boat will float 290 pounds before the chines start to enter the water. Beyond that I would expect the boat to slow noticably, although boats with bows shaped like Vireo are superior in this respect. So you see that it is a push to float two large adults in the 12' Vireo. The Vireo14 will float the same way at 400 pounds and will be much better with the two adults. Hull weight will increase by 10 or 15 pounds, of course.
Vireo14 uses taped seam construction needing four sheets of 1/4" plywood.