I was at the Toronto Sportsmen's Show over the weekend and ended up picking up a Turning Point 21p 4 blade prop for my 19ft fish'n ski. I found that with a 23p 3 blade, it would plane out real slow when loaded but cruised at a higher speed for 2900-3000rpm by 3-4mph. The 21p 3 blade would plane better but had the slower cruising speed, so I figured I'd try a 4 blade. I'll report later in the season after I splash the boat in May.