Truly, I don't know your engine, but just as a S.W.A.G. (Simple Wild Assed Guess) I'd think that a 20p prop would be too much. 15-17 would be my guess for that HP...19 tops. We all know the drill.... See what your engine makers recommendions are for WOT, then get a prop that lets you hit that number but not go hugely over it. That's the proper size prop for your engine.
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God) 
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.
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