We bought a new M15 and bought also a new 2hp 4strk HP Long Shaft. The newer Montgomery boats have an adjustable motor mount with three or four notches. At full power with two people in the boat, the motor mount itself is about 2-3 inches under water, creating an indeterminate amount of drag. Still moves pretty good! And quiet! I have decided to add another notch to the adjustable motor mount this winter when I have the boat home to minimize/eliminate the drag problem. I would speculate that the short shaft would work, though you would have to push the mount down further, and the distance might create a reach hassle for anyone in the boat. Knowing what I know now, I would still get the long shaft. Besides, I believe it is what Montgomery recommends. Oh check prices everywhere! In our area, Northern Idaho, I got prices ranging from @800.00 on up. Regards, Vince and Sharon Himsl (Duet)