finding the right prop

[shine]

looking for feedback on finding a prop...

My boat: 23 CC rebuilt a little lighter than stock. Yamaha F225 on a bracket.

First prop was too small; 13.75" diameter and 17 pitch aluminum, it ran too high RPM.

Second prop caviation issues; 15.25" x 19 pitch, but it was a vented prop (holes in hub at base of each blade).

The second prop performance was a little strange to me. While the first prop held a nice grip until the motor was trimmed up more than half, the second prop would cavitate at anything other than all the way down/tucked in. At slow speed it was tolerable (although I could feel it a little), when running anything over 4100 the venting really was noticeable. I was still able to get 6000 RPM and 40 mph - lightly loaded. 22 mph at 4000 into (we had at least 15 knt wind), and 25 mph at 3800-3900 down wind.

Another wrinkle: second prop hub diameter is 1/2" or so less than gear case. It stood out to me as not looking right. below is a picture. Im sure this could explain a lot of the cavitation/venting also, there must be a huge amount of suction generated by such a drop in diameter.





I sent the second prop back by UPS today and will see what the shop sends back for prop #3. Seems like a 18 to 18.5 with a 15.25 diameter will be just right

Any ideas on that hub diameter?