we have one in our club, the owner went down an unusual route and fitted some astro cobalt electric flight motors, not cheap motors but they do the trick !
for power he used some cyclon lead acid cells each is a bit bigger that a torch cell ( D cell ) but is only 2 volt, but he lines up 6 to make a 12 volt pack, capacity is 5 ah
the boat planes nicely... in fact when he ran it a beale park 3 years ago he was swamped when he took the boat out of the water wirth people quizzing him on the set up !
the props are small ( well for a boat of this size) they are 2 bladed and i guess from memory about 30 - 35mm, but they rev nicely and due to their fairly small size dont draw too much current... run times are in the region of 30 mins
the boat is as light as possible and some detailing is changed / modified to make it lightweight but it does look the part out on the water....
but flight motors are not cheap , but maybe some of the motors inc brushless from the far east may be worth looking at ?????