rob i used a.60 sc aero engine on my boat 3 ft long and it did 30 pluss submerged drive i got the flywheel to match and water cooled it using coils.pm me if your interested as its doing nothing right now!!.this engine will give you good speed for your boat as is if you went surface drive id say 40 pluss easy.it starts easy using a plane starter and v belt.just needs the plug loosening to start it as it has high compression then tighten back up when its running and off she goes.