Hi Balto Charlie-
I did the C&O in one day a couple of years ago. There were two of us (which makes motivation really important). We travelled really light-- mountain bikes, two bottles with gatorade (and powder to make more), a camel back with water and energy bars, fig newtons and a couple of sandwiches. We planned on 14-15 hours and ended up doing it in just over 13. We didn't stop except to refill water at the convenient pumps along the way and to use the 'don's-johns'. It was a great ride. We rode from Cumberland to DC--the 'downhill' route. We also did it in late June, to take advantage of the long daylight hours. In addition, I carried a little flashlight for the tunnel--and for the first half hour of the ride, as we started early in order to maximize our time.
I had a rigid bike, and in retrospect, it would have been nice to have a suspension fork, as it was rough--my arms were shaking all the way through the ride- Tony, on the other hand, had a full suspension bike, and he bounced arounda lot too, but his arms didn't seem as tired. Make sure your saddle is comfortable--there really isn't any reason to stand up to pedal-as it is mostly flat.
As an aside, a friend and I are talking about doing a 'double'... DC to Cumberland on day 1, and Cumberalns to DC on day . That is a long way.
I highly recommend the ride. (Oh- Iwas in my late forties when I did the ride--I'm 51 now).
train safe-