I'm pretty sure you can get 4 kts from 3hp on a Catalina 22. I get 5.5 kts from a 3hp Epropulsion equivalent on my 19ft Mariner (1400 lb displacement). Mariner sailors with 4hp outboards get the full 5.6 kts hull speed. However, if you use an electric, you do NOT want to run at hull speed or even close - you waste your battery too quickly. Power vs speed is NOT a linear curve. On my Mariner, I did 1 mile trials in both directions using GPS:
- 1000 watts (full power) = 5.5 kts
- 400 watts = 4.1 kts
- 300 watts = 3.5 kts
So the correct answer depends on what you want the motor to do. 6hp if you want to power at hull speed with the big wake, gas if you want the noise and vibration (electric gets pretty costly above 3-4hp). If you are just looking to get away from the dock, go through bridges, back to the dock, anchor, etc., the 3-4 hp is sufficient. Electric will put a smile on your face and a higher initial cost. Electric will be more reliable, and your shoulders and back will thank you. Gas will have a lot more range with even a 3 gal tank. Solar can help with electric range, but space for solar panels is very limited on smaller boats.
I traded starting anxiety with a 30+ mile range (5hp Honda) for 12 mile range but no starting or maintenance worries.
My ODay 25 (4500 lbs) had a 9.9hp Chrysler 2 stroke. That was overkill for that boat.
Fred W
Stuart (ODay) Mariner 19 Sweet P