Sorry if this is a dumb question, but can you use a long-shaft outboard on an air floor inflatable? I would imagine that it is bit problematic if you are landing/launching on a beach, but are there other problems I am missing?
I've had a short shaft Mercury 2-stroke on a Zodiac RIB and a Honda BF100 4-stroke long shaft. The weight difference was about 30 pounds, I got up on the plane faster with the Mercury, but my planing speed range (once up I could throttle back a bit) was better with the Honda.
I much preferred the Honda, despite the weight and its age (1985 vs. 2000). In fact, I sold the Mercury last year. Smoke and noise were excessive on the two-stroke.
Because the shaft is longer, you need to experiment a bit more with the tilt setting.
The Honda had a Doel fin, and I found this made a huge difference in planing and control.
I can't see how the air-floor's going to make a difference as long as the OB is properly sized to the inflatable. Just as an aside, we've given up planing and gone to a Honda 2 hp 4-stroke, due to the air-cooling and the sub-30 pound weight. My wife, whom you've met, can one-arm it on and off the boat. That consideration trumped all others. It pushes the Portabote you sold us at nearly 5 knots, and 4 knots loaded, so I can't say it's too small.
The biggest problem with a long shaft motor on a short shaft intended boat is usually that it creates alot more drag in the water than its supposed to, not really a problem if its not going very fast, but really inefficient at any kind of planing speed. Other than the aforementioned hitting bottom before it normally would.