I have recently built a 4.5m aluminium catamaran and have spent a lot of time testing to get the optimum set up for the motor height with a number of other modifications (extending the hulls, centre sponson).
I have been testing it in all sorts of conditions in a local river which is very wide. Into the wind and waves it goes like a cut cat (no pun intended) but when going down wind it (the motor) really doesn't like it. There are no waves to speak of just surface ripple.
I'm just wondering if anyone knows why this would be?? It will be creating lift going into the wind but I don't know why I can't get the same sort of performance (it's a fishing boat predominantly but wanting to do the occasion biscuiting with the kids) either way. Not that I'm looking for performance per se but just don't want the motor to bog down like it does depending on wind direction. Any help appreciated...

sailors know it as 'apparent wind' 

Hey mate,
I don’t have any answers to your question but have a 4.5m cat myself. If you’re interested in checking out my setup, or just discussing small power cats quirks, let me know. I have a few questions of my own. I think it’s a great platform though.

Update: I think I've nearly cracked it! Went for a run I the river yesterday at Foxton. There was a fair breeze blowing at times up and down the length of the river so it was good to test into the wind (optimum) full throttle and very quick again with lots of wind being pushed into the tunnel creating good lift. The runs with the wind behind us initially were frustrating because there was a noticeable difference in performance. I found opening it up to full throttle made it run better with the outboard liking it more. Still about 80% of the into the wind results but I was happy enough.The lower down revs not so much. Again more wind forced down the tunnel...Also this was the first time I tried the longer anti-cavitation plate that I made. I think it made quite a difference when trimmed up. The new plate extends around 100mm longer to the rear.
While we were there my kids and I tried out their new ski biscuit which went well too!