A michigan wheel 3 blade sailor prop has a disk area ratio (DAR) of 0.44 while a 2 blade sailor has a DAR of only 0.36. The smaller DAR means that at the same pitch, the 2 blade prop moves less water than the 3 blade. To get the same push from the 2 blade prop you need either more pitch for the same rpms or higher rpms. So it is completely normal for a 3 blade installation to use less pitch than the 2 blade. Simply based on the ratio of the DAR's, the 3 blade prop would need 7" pitch to match a 9" pitch 2 blade prop. Of course it isn't as simple as all that and the actual pitch differences aren't that large. Quick calculations suggest that you would get about the same performance with a 3 blade prop pitched to 8.5" as you would with a 2 blade pitched to 9"