4 blade for skiers and towables....... yes they make that much of a difference... thrust increase out of the hole... if the "other issues" in shop are engine related once that's resolved and your operating at peak efficiency, toss your initial finding out the window, everything can change....prop choice varies with engine health, some boaters have engines not performing at peak due to correctible issues, they put less prop ( less pitch) to get within the recommended rpm ranges running with what they have.. here's an example... as to me...had boat for 2 years.. tuned up. seemed to need 15 p prop to get me 4800 with the 3.0 merc I have... another tune up this spring, noted was loosing belts to often and too loose... noted the alternator arm bracket for belt tension was cracked, put new arm on, tightened it up...belt not slipping, electrical improvement..... yesterday took boat out on Seneca Lake NYS fishing, first time out for me....me and son, had 15 p 4 blade Solas.. was putting around mostly, got on plane, put the hammer down.....tac= near 5000 huh? Im going faster than I ever have in my 20ft cuddy....with a little 3.0... odd, same prop I could only hit 32 with wind at my back downhill at 4800, near 5000 Im doing 34... GPS speed......that's never happened before..... so I got home and tossed on the (back up) Michigan Match 4 blade 15x16P... guessing that's going to bring me down to recommended range and might even hit 35...
so with that said, so many variables go into prop selection, it's all relative to engine health, load.. and other things experts here can tell u about, learn as you go.... good luck
