I built the Chris Ostlind design 18 foot compact double. You can find the design on Duckworks along with a picture.

I did not use a rudder as it t is short enough and with just 2 chines, lean turns well. Great for my wife and I. I have no trouble with novices allowing me to lean turn the boat. It teaches them a little tolerance for not sitting level. For your use, you might think 18 to 18-6 hard chined boat to be able to go rudderless. The cockpits are about 25 inches from front of 33" cockpit to back of the other cockpit (measured from photo I have on my computer.

: Thanks Duane, exactly the sort of info I was looking for. Not sure
: I will ever build one but I do want to design one.

: If I did build done it would be to use with a newbie paddler and
: introduce them to the sport. I live inland and big waves mean
: really bad weather, the kind you are not out on the lake in on
: purpose. Well smart people that is, so the excludes me. My
: favorite place to take new people are some of our sheltered
: creeks which get narrow towards the end. So a rudder would be a
: great thing in tighter quarters I would think.

: Thanks again, just the info I needed.