Depends on load and if you mount the engine at proper height. and whether or not you want to turn it into a 60hp by removing the air intake air restricter. Leaving as a 50hp with a light load (400#) start with a 14P or 13P for a heavier load. If you change it to a 60hp, then go with a 15P. This is assuming the 764# dry weight of the boat is correct. Should get ~36 mph as a 50hp, and ~40 mph as a 60hp.
