Have recently changed my prop and lifted my engine up one hole for a pretty decent change in economy. Boat is a Yalta555 with F115 Yamaha. Went from the 17k yammy prop to a 131/4 x 17 Solas new Saturn. Lost about 4-500RPM at WOT but gained a lot better mid range performance. On flat conditions a good cruise is 3900rpm doing 23knots and using 19lph. Went offshore yesterday and it got a bit bumpy on the way home so was doing 3600rpm for 20Kn and using 17-18lph. All up yesterday did 128km on the GPS Trip meter for 61 litres. On average the old prop in same conditions yesterday would have used around the 70-75 litres. WOT now have gained a couple of knots from around 32-33 up to now around 35 at 56-5700rpm and uses 40lph at this.