mmmmmmmmmmmmmmm according to GOOGLE, the 720BB = 4100 RPM no load......is a bb720 and a 720BB the same item?
Speed 720 BB TORQUE SMC-M-6372
Nominal Voltage 12.0v - Voltage Range 6.0 - 13v - No load RPM 4,100 - No Load Current 0.75 A - Current @ Max Efficiency 3.0 A - Stalled Current 13A - Max Efficiency 75% - Case length mm 72.0 - Case dia. mm 44.5 - Free shaft length mm 6.5 - Shaft Dia. mm 5.00 - Weight (g)380
Optimal paddle shaft speed for a model paddler of 5' is in the order of 150 RPM....with the ability to reduce that further with a speed controller....so if a bb720= a 720BB then you would need a reduction of say 25:1
Log in & have a look @ our paddleducks.uk WEB site
.........you will find many references to this & discussions on common/single shaft drive as very few paddlers used independent drive for each wheel.... Derek