What is size boat prop can I install for heavy loads?

I have a 1989 Chaparral 187XL with a stock prop that is 13.75 x 21. The prop is very beat up and I want to replace it when I winterize it. I was wondering what size prop I could go with that would help get me planed out with a heavy load? Or, would replacing the stock prop with the same size give me that extra little bit of power I need? There is not a crisp edge on any of the blades, thanks!