Propellers...

I operate Performance Propellers, (CDI propellers). This not intended as a sales pitch but to present the data that I have about the Catalina 30. There has been some discussion about the best prop for the Catalina 30. I have found that there is no single best prop. Here is my data for the Catalina 30. Based on measurements of approximately 25 boats of varying ages to average prop space, historical records of motors installed, conferences with a major supplier of equipment for the Catalina 30, and historical performance with CDI props.

LWL: 25' list displacement 10200 prop calc disp 11220 (The 10200 is an empty boat the prop calc loads the boat.) Hp range 18.5 to 22.6 as needed for (est) hull speed of 6.7. This is the range of hp needed if the boat is going to be able to reach hull speed under power alone. This is a seldom seen ideal condition but sometimes useful as a diagnostic

Assumes open water prop space with greater than 15 inches to rudder, Centerline of shaft (at fixed prop blades) to hull is approx 8",prop dia 11 12 13 14 15 and clearance% 22% 16% 11% 7% 3%. Note Propellers must have between 15% and 20% of the propeller diameter as clearance between the propeller and any other part of the boat. Less clearance means noisy and less efficient propellers. Tight clearance contributes to Prop walk. Think of the clearance as hydraulic rather than mechanical.

HP @rpm ratio motor 2 blade 3 blade propeller 2 blade
11@3000 (2:1) M5411 13X10 13X9 13X10
14@3200 (2:1) M-18 13X10 13X9 13X10
30@3000 (1:1) A-4 12X7 12X6 12X7
18@3600 (2:1) M3-20 13X8 13X7 12x10
21@3200 (2:1) M-25 13X12 13X10 E14X11
23@3200 (2:1) M-25XP 13X12 13X10 E15X11
18@3600 (2.61:1) 2GM-20 13X10 13X9 E15X11
27@3600 (2.21:1) 3GM-30 13x12 E15x11
27@3600 (2.61:1) 3GM-30 13x14 E15x12

The E is an extendo prop that moves the prop aft 6 inches allowing for a larger prop. As you can see from the chart most recommendations are 13 inch maximum and the pitch is changing to make up for HP and gearing differences. Pitch for diameter changes are common when there is a close clearance as found in the Catalina 30. Normally there is a 1 inch diameter difference between 3 blade and 2 blade propellers as well as a pitch difference. This too is a sign that the boat is prop diameter constrained.

The prop diameter and pitch shown can be fixed feathering or folding. Various prop manufacturers will have slightly different recommendations based on blade configurations and their experiences with the Catalina 30 etc.

Larry