Mark,
65 kg would be the max if you raced it but I put enough in it so its comfortable at 120 kg (kid & adult) also. Best range would be 40-50 kg.
Hull transoms and/or narrow hulls have nothing to do with narrow, its all about slightly lower drag and minimizing the pitching. The 2 hulls show are actually quite different but both do the same thing more or less. The round bilge hull has more than 8% less WSA, is more than 6% fatter and almost 10% more WPA and a fatter transom than the hard chined version, yet the pitch rates are almost identical (within 1%) so just looking at physical sizes has very little to do with the dynamics. The thing you might have missed is that the chine goes downwards for a long ways aft before it rises again, is quite good for keeping the transom out without having a big fat shape at the back that just drags water. The other thing to remember is that if you can keep the pitching under control, you don't need a lot of reserve buoyancy at the back to counter stuff thats not happening.
Wouter,
197mm longer
RG