Your “115” E-TEC is probably about 125 hp at the prop.
You’ll first need to make sure your AV plate is above solid water before you do too much experimenting with props. Also make sure your tach is accurate - analog tachs are notoriously inaccurate and can be off by several hundred rpm, so can cause you to pick the wrong prop! IF you don’t already have one, I’d recommend one of the Evinrude digital tachs that plugs into the engine computer.
My Seafari used to top out at about 32-34 mph at max load with my old 1975 V-4 115 (rated at power head back then; it was probably about 100 hp at prop.) My best prop was an OMC SST 13 3/4 X 15 3B stainless prop. The blades had enough cup that I was able to raise motor 1 or 2 holes that let me pick up about 3 mph compared to the same size aluminum prop, so that’s a good improvement once you find the right size aluminum prop.
If you haven’t already done so, check out the E-TEC Owners group website - they have tables for all the various motors showing the OPTIMUM WOT rpm, which is what you want to shoot for. The V-4’s have a 2-position valve in the exhaust that’s prone to sticking if you over-prop the motor and run cheap oil, both of which will cause carbon build up. Best to run XD-100 oil and have dealer set it up to run only that oil, as it will run ~ 100:1 mix and not carbon up.
Check out my Sticky post on prop testing In the performance section - lots of tips there on how to find the right prop.
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