I have located a rebuilt prop for my Johnson motor. However, my existing prop is 12 1/4 X 15 and this one is 11 1/4 X 17. The price is right and I want it only as a spare. Can someone advise what effect the smaller size and pitch will have on my motor, if any. Boat is 16 1/2 aluminum Pro Fisherman and motor is 50 HP.