Frans Faase writes: "The Ping Pong gun or Ping Pong bazooka has been a popular and compelling tool for physics education. However, the design necessarily means the ball emerges at subsonic speed. The design has been modified to include a pressure chamber and a convergent-divergent nozzle, similar to the design of some supersonic wind tunnels. This modification results in supersonic speeds. The current design has achieved a launch speed of 406 m/sec, about Mach 1.23."
I've never been canoeing before, but I imagine there must be just a few
simple heuristics you have to remember...
Yes, don't fall out, and don't hit rocks.