I am doing my very best to try to figure out what props my boat originally came with and the best pitch and size for the boat, info: 1989 35 mediterranean, gas powered 454 crusaders. Current props 21x24 4 blade. 1.75 shaft. The boat usually has a heavy load on it but even with just my self, no water, and 1/2 tank of fuel it seems very sluggish. The engines and transmissions are great and are operating to spec. I know they originally came with 3 blades. My wot rpm is about 4200, from what I've read this is pretty close to normal for my set up. But 21x24 seem a little over kill and expensive for a new set. Just want to make sure if I'm gonna spend the money it's on somthing that's proven on the water and not from a prop calculator. Thanks for the help