Motorized speedboat from Technic Catamaran alternate model?
With a few Power Functions elements and a pair of propellers, I was able to build a motorized boat similar to the alternate model.

1x: 8881 Power Functions Battery Box
2x: 8883 Power Functions M-Motor
1x: 8884 Power Functions IR Receiver
1x: 8885 Power Functions IR Remote Control
2x: 30332 Propeller 3 Blade 9 Diameter

See it in action!
click to watch the video
Pictures
floating, side view
floating, front view
Close-up pictures on how it's built
propeller motor closeup
center structure closeup
Conclusion
Overall it works pretty well, and the hulls are surprisingly resistant to water leaking inside of them. The only major issue is that direct sunlight can interfere with the IR receiver at a distance. As an alternative, the IR receiver and remote could be substituted with something third-party like an S-Brick (uses Bluetooth). I didn't have any of the smaller and lighter LEGO Powered UP controller and motors, but with some redesigning that could also be an option (also Bluetooth).
I also hope that someday LEGO will make some propellers which are a better size/shape for use with water, and maybe this boat could go a little faster!