prop size

Dec 2, 2013
9
Irwin 43 CC MKII Vancouver
I have a 43 Irwin CC MKII 1986.
I will need to change My prop soon, I think the specs call for an 18 X 17 prop.
But I have a 19 X 17 on it. The shaft is 1 1/8 and it looks pretty small for the prop
size. So I assume it was changed in the past, I thought the boat was too fast ( but I am
not complaining tho LOL and pretty cheap on fuel too )
Should I go back to the original size or leave it the way it is. And will an over size prop
hurt the boat ?