prop survey

[Destroyer]

Originally Posted by tnltracy

I have a 13-3/4 x 15 aluminum currently. Last year I was getting around 24MPH at 5500 RPM by GPS. Start of the year I was showing around 29MPH, but her butt got a bit dirty over the summer

At WOT, the motor would over rev well over 6k RPM, so I've been shopping for a new prop this year. I just picked up a used 13-1/4 x 17 that I'm hoping will take RPM's down a tad and give me a few more MPH's. Will report once the boat gets into the water

Pitch is the theoretical distance that a propeller will move through the water in one revolution. (not counting slippage). So a 21p propeller will move 21" through the water in one revolution...a 15p will move 15" etc etc. As a general rule of thumb, expect to see a 300-400 RPM DECREASE for every 2 inches of pitch that you INCREASE your prop. (Propeller pitch is normally changed by a factor of 2"....13,15,17,19 etc.) Find out what the recommended WOT RPM's are from your motor's manual, and then size your prop until you arrive close to it. If you are into watersports like tubing or sking you'll want to go down one size in pitch, which will result in better pulling power and faster hole shots but less top end speed. If you're into going places in a hurry you'll want to go up one size in pitch which will result in a faster top end but less pulling power and longer time to get up on plane. In all cases stay in the recommended RPM range.. over-revving or lugging your motor will result in a greatly shortened motor life.