I had the same problem, in the end I went for the Tinker and a set of wheels, I use a Mercury 4hp 2 stroke, but the 3.5hp I had was incredible light and seemed as powerful as the 4. It would JUST plane the tinker with 1 adult and a 10 year old.
I did have a Honda 2HP 4 stroke but it was a bit weedy compared to the 3.5 and spilled oil all over the boot when one of the kids moved it!.



He never did care for the river, did Montmorency.