Am I missing something here ?

[Jake_Daddy]

Hello new member here. I don't want to hijack anyone's thread but I was about to start a similar one. I have a new to me 20' Sweetwater with an old 90hp 3cyl Mercury. I have had the boat a couple of months now and it runs great but I have been suspect of prop issues and way to much slip. I just got the gauges all working last weekend and finally got to run some slip calcs. I have a 16P stainless quicksilver prop which is a bit oversized as I am only hitting 4800 rpm at wot and my top speed is only 20mph per gps and playing with the trim does not make much difference in rpm or speed. That is coming out to over 35% slip with me the wife and two little ones it's also what the previous owner told me top end was. I know I need to get into a 13P or maybe 14P if I can find one but I also ask...am I missing something here?

Also my last boat had same motor on a 24' fishing barge and it went 24mph, don't remember prop on it though.