making a High-Thrust outboard

I have been looking at a high thrust auxiluary outboard for my catamaran (centre-pod mounted) and the classic 4 stroke 9.9 Yamaha High thrust while a great motor is a bit short on horsepower, Yamaha also produce a 4 stroke 25hp high thrust model but these are way expensive and heavy.
I was wondering if I could get a 20hp 4 stroke and mate it up with the 2.42:1 gearbox from a 9.9, what could be the possible downsides...
- they are strong but would the extra hp be too much for the gearbox
- is there enough space for a enough blade area
what do the experts think of this one...

 

Yamaha also produce a 4 stroke 25hp high thrust model but these are way expensive and heavy.

Find a used version of what you need.

 

I agree, the yamaha 25 is a huge engine.

You may find a kicker style outboard suits, or check out fitting a 4 blade prop instead Honda do that on their smaller outboards to increase thrust. Or do as fast Fred suggests, I recall some high thrust outboards in the 15-25 sizes or maybe an older Yamaha 25? We had a 2003 model on our previous powercat that was much smaller than the newer version

Richard Woods of Woods Designs

www.sailingcatamarans.com