We bought a 17' Bayliner new in '07, 3.0 Merc Alpha One, it came with a 15x19 prop, worked okay... Meanwhile our boat neighbors had a 25' Bennington Pontoon, 5.7 Merc Alpha One with a 14.5 x 21 prop. When loaded down they were having trouble getting on plane. So we switched props-- my prop made a BIG difference in their plane time, and they never ran the thing at WOT so they were VERY happy. And with their prop on our Bayliner, I lost zero plane time, lost about 100 rpm on the top end but cruise RPM dropped by 200 rpm, and top speed went from 40 to 43-ish, all of which made ME happy. They're still running my old prop, their prop went with the Bayliner when we sold it in 2011.
Ergo- if going stainless, I'd suggest a twin to mine, 14.5 x 21, same as your current prop just a bit bigger diameter. If you want to go down to a 19" pitch, I'd say get a 15 or even a 15.5" diameter. But honestly, even with the 21 on the Bayliner it would plane in less than 4 seconds with us and 2 dogs, at 4200' altitude.
Last edited by Frantically Relaxing; 11/20/19 12:31 AM.