23 cc 250 mercy prop size

[Schoolbd]

The boat I'm speaking about belongs to my son, he just purchased the 2017 250 optimax , haven't gotten it back from the boat dealer yet , should be getting it any day now , just wanted a little help with correct prop size, I've owned to 20' sea crafts over the past 30yrs but have no experience with the 23, can't hardly wait to go for a ride in it