He will be best to go with electric. It is a lot less work when you want to go run. Some electric's are the fastest boats just look at youtube there are rc boats going 100+ mph. You dont get any better than that with electric you can run all day there is no burnt glowplugs no fuel to worry about. And look here at how many post about adjusting carbs. That is most people's nightmare. You can just plug and go. Here is a few you can watch there electric.
http://www.youtube.com/watch?v=MR-6d...eature=related
http://www.youtube.com/watch?v=U32pikSS-yc
http://www.youtube.com/watch?v=VDsBK...eature=related