I think the standard prop was a 9×8. I have several 50th QD and on my 14 foot tinie the 9×8 works pretty good. I know others will comment about bigger pitch. I usually have two tanks of gas and a spare motor, just in case in my boat. Point being the heaver your outfit the less pitch you need. I have several 15hp props and I have tried them on the QD’s and lost some speed. The big pitch props will make the motor seam sluggish. 15/18hp are usually 9/10 or maybe a little more.
In my humble opinion a 9×8 or a 9×9 is probably what came with the motor.
dale
get’em wet!….don’t let’em set!