enough h.p.?

i was trying to get my friend into wakeboarding this summer and i finaly succeeded and he bought his own board(a cheap hydroslide 135 cm)the problem is our boat only has a 115 h/p motor and his boat only has a 90. hes pretty big(6,0 160lbs)and the boat just draggs him through the water until he cant hold on and has to let go of the rope. so he never gets to the point where he;s able to stand, do you think the board is too small, or is the motor? im pretty sure its not his technique but hey I could be wrong.