Hi Guys -

I've built a few boats but this is my first airboat. Hull is wood/fiberglass and is around 11' X 5'. The only real issues I've had is figuring out the motor and reduction drive. Please let me know if I'm on the right track with this...

The motor is 22hp (max 4000 RPM) that generates a max of 33.19 ft/lbs of torque at 2500 RPM. I'm looking at a 50'' 2-blade wood prop that has max power when tips travel at 890 ft/sec which occurs at ~4000 RPM. So if I'm reading this right, I'll have max power from the prop at 4000 RPM, which means a direct drive in my case. However I'd be generating max torque at half that speed. What is more important in an airboat, max RPM or torque? Since the motor could not turn the prop over its recommended max is a reduction drive needed? Thank you for any help with my newbie questions. From what I've read the RPM/torque/DD/RD solution is part science part magic.