Ultimate Utah fishing boat.

[Paddler]

I chose the 115HP because it was the highest state of tune for the block.

Please explain further what you mean by this statement?  Thanks.

Most outboard powerhead blocks are shared with at least 2 or sometimes 3 horsepower ratings.
The changes in horsepower ratings are determined by carburetors/injectors, fuel mapping/timing,and exhaust system tuning.
Jon’s 115 is probably the same block as a Mercury 90 hp, just ‘tuned’ to put out more hp than the 90.
No different than how Mercury, Yamaha, and Suzuki 9.9 and 15 hp kickers share the same block ( per manufacturer) but the 15 hp engines get tuned to the higher hp.

Thanks

Yep, as I said before, Mercury's 2.1L I4 is available in 75HP and 90HP versions.  To get more than 115HP one needs to go up to the 3L block, which puts out 150HP.  The redesigned 150HP came out in about 2013, and it's a helluva engine.  Larger displacement than the previous engine, 2 valve instead of 4, no valve maintenance ever, lighter weight and more fuel efficient.  That same design philosophy trickled down to the 115HP a year or two later.  Awesome engine.  On a typical 135 mile tuna trip, with 2-3 guys, full fuel (52 gallons), all the gear, a 150qt plus a 100qt cooler full of ice, I'd get 4MPG with the old engine.  The new one consistently does 4.5MPG, which gives me a range of well over 200 miles.  Typically, though, as a safety precaution, the usual recommendation is 1/3 of your fuel on the way out, 1/3 on the trip back, leaving 1/3 in the tank back on the dock.  On a nice day I'd probably go out 70 miles or so, leaving enough to troll a few hours and still not have to worry about fuel.  On a side note, I've found that the fuel meter in the Smart Craft gauge is very accurate, within tenths of a gallon.

Went fishing today, fish had lockjaw due to the cold front, 8F water temperature drop and much increased turbidity.  I happened to check the USCG hull plate and discovered I'm even more underpowered than I thought.  The 20' Searunner is rated for 175HP!  What was I thinking?  The 175HP 4S is a DOHC 3.4L V6, weighs 475# and costs ~$6800 more than my 115HP.  Add in the kicker with controls and I could have spent another $10K or more without improving safety or catching more fish.  I must be crazy.