im looking for some help i order a 4 blade prop 9 1/4-10 for my 15hp 4 stroke motor 4500-5500 rpm thats is the same size prop that came with the motor.but yesterday i got a phone call saying it is on back order and it wouldnt be in until late march so i went with a 9 1/4-11 three blade.well that be alright for my motor.