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You've neglected to account for the additional cup on modern ss props which creates greater effective pitch. I run a 13.25 x 15 Stiletto Advantage 1 on my 15 with the F70 and i have found the 17 hull works well with about 2" less pitch than the 15 takes. The Stiletto is an aftermarket prop, but they also make Yamaha branded props if you are looking to pay more for the same chunk of metal.

But as with any prop advice - it's not perfect, trial and error is needed to find the right answer.