Re: 12 3/4 X 21 prop for 1988 V-4 88 horsepower Evinrude SPL
First-order approximation, to be verified by tach readings, would be 21" pitch on a light 15 & 1/2 footer, 17" pitch on an average 17 footer particularly if you ski, and 15" pitch on a heavy 19 foot deepV cuddy.