i have just finished putting together a ski for a friend of mine 3 inch short XFT 5mil dasa p/v 48 novi's total loss i was recomended to get a 13/18 skat trak for the 144 magnum but i bought it and when i went to put it in i found out we have a 140 set back pump so what would be the apropriate prop for a 140 pump if a 13/18 is for a 144