Nice lil project
What's the lenth of the boat
If it's near 24" the largest prop I would run would be twin 45mm counter rotating,4 blades
Check out www.cornwallmodels.com lowest prices and fast shipping.they have any prop size u can imagine
If it's smaller than 30" I'd recommend one or two intgey lathe motors or rock crawler motors,35-55 turns.my 30" boothbay lobster boat ran a 45 turn direct drive with 1.5 hour run times,boat went 15mph and plenty power and low speed control.motor would be 80 degrees after a long run so water cooling wasn't needed

Your boat can run single screw also
Oh my 45 turn lathe turned a 3 blade 2"(50 mm) prop with no problems