One option to repair splits and slices in plastic boats is hot air plastic welding with compatible plastic welding rod. Check out this excellent video on how to weld a plastic boat submitted by 4CRS aka Four Corner River Sports. Check out 4CRS on YouTube videos for excellent paddling action:
This is also a very viable technique to repair all kinds of plastics in our gear, including ski boots (cracks and holes) and ski/snowboard bases. We’ve been experimenting with some base repairs with good results. One concern is controlling the temperatures and air dispersement so more than the repair area is not affected. With a digital heat gun and small nozzle, it’s been pretty straight forward and encouraging so far.