Annacat:
I have a 2hp gas 4 stroke gas auxillary motor mounted on my Tandem Island that I use for emergencies (loss of wind, breakdown, etc), I have had it about a year now and it works prety well, it propels my TI at around 5mph, and I can go about 40 miles on a gallon of fuel (I always carry at least a gallon). I saw the Cheata motor mount on their web site and it look like the motor I have would fit and work. You can see pics of my motor on this forum thread (The Ultimate Tandem Island (Hydrofoils, Spinaker, jib,etc)
viewtopic.php?f=69&t=33720. I bought the motor from Florida Outboard Motors and Engines (
http://www.ioutboardmotors.com/20hpoutboard4cycle.html), it cost $525 and does the job. When you get the motor it would be a good idea to clear coat the motor housings and all the parts before putting in salt water. I didn't do that and alot of the screws and bolts rusted pretty quickly, even though I rinsed the motor off after each use. My motor mount was home made so it only cost $15 or so, but on a cat you will need something better. The motor only weighs 20 lbs so, and tilts up and down it shouldn't affect your performance like a 15-20 lb electric motor and 1 or 2 60 lb batteries would, plus where in the world would you put the batteries and cables on an H16 or H18, and what do you do to get back in with dead batteries (paddle ??). What I do is start the motor and lock the throttle and steering, then use the regular rudder to steer. The TI is much larger than a cat so you will likely do a little faster than my TI, you won't be pulling any skiers, but it will get you past your bridge. With the motor you can sail into the late afternoon without fear of getting stuck out in the the dead sunset wind (at least around here the wind always dies in late afternoon and you have to paddle back in (which sucks)). Hope this helps. Bob