I would like to add this conversation as I have been experimenting with this same hull and engine config.
115 EVINRUDE ETEC on a 2015 Triton TX18/Ranger RT188
21P LASER 2
TRIM TABS removed
Vance 6" manual jack plate
1/4 tank of fuel
fortrex trolling motor up front.
Back story is while running the boat one afternoon either my lower unit let go or hit an object (still inconclusve) however I had to replace the lower unit and all that was available, other than a brand new 5000.00 assembly, was a new pull off of a 90hp etec (same part#) that was replaced with a jet pump. Turns out this lower unit had a 2.00 gear ratio which in turn dropped my RPMS to 4900 at WOT, while i am still running the same GPS speed of 47- 48 mph. Now im forced to lower pitch to bring the RPM's up to within the engines powerband.
Question is, will this hurt my top end by going with a 20 or 19 pitch prop, stay the same, or increase due to increased RPM and power.
I would love to hear your thoughts. Thanks!