Hi,

That engine should swing a 16" prop with no problem. Thrust increases greatly with diameter though, and in your case you could trade diameter for pitch. What is your expected speed of the boat? You can pitch for the expected speed at max rpms, and adjust diameter accordingly. That engine could probably swing an 18" x 4" prop at around 8500, which would provide a theoretical pitch speed of around 32 mph, and a good deal of static thrust.

Good luck and post pics if you can,
AV8TOR