[Fr. Frank]

BTW, I also run a PowerTech prop, although mine's a custom 15X16.5 pitch, behind a 1.64 gear ratio.

Calculated slip ratio, properly trimmed, is about 11% with this prop, an excellent, very low slip ratio. My experience is that most props, even high-performance props show effective or "apparent" slip ratios between 15% and 20%, depending on the application.

The weight of the load, depth of the prop, angle of attack, all obviously make a huge difference, as well. Having a prop with excessive pitch that will not turn up into the powerband of the motor can give you slip ratios approaching 30%

For instance, a very well set up high-performance bass boat might show an apparent slip of only 8% to 9%. A 23' SeaCraft will be doing very well indeed to get below 18%

At any rate, my max RPM behind the new lower unit gearcase now is about 5900. (Old case w/ nosecone was 6100, with slip of 10.5%) I also went with the lower pitch prop for loaded holeshot and acceleration under adverse sea conditions. The motor also doesn't strain as hard at cruise rpm of 3900 - 4000, about 32-33 mph.