I built a 489 stroker motor for my boat and think I need a new prop. im running a 21p rev 4 and getting 5400 rpm on a trs drive. I think there is to much prop slip and was wondering what the prop slip % should be on this boat, and what size prop I need.

What is your speed at 5400?
Has the propeller ever been repaired or reworked?

Brett

my top speed was 73.4 on gps at 5400 the prop I bought brand new couple years ago and still looks new to this day

If we use 1.5 as you gear ratio, your slip is negative. This is impossible since you can't actually have a negative number. This would mean the forward travel of the boat is farther in one revolution than is possible with 21 inches of pitch. Something is wrong.

Brett