RE: CAT 3208 T's and running bigger twin diesels
"But somebody must think one would burn less fuel that way or this conversation would not be taking place. "
The point of the exercise is to INCREASE the loading on the single engine to save IT , not the fuel it burns. Extra fuel is cheap, compression fix on a throw away engine would be costly!
Unfortuniatly the simple offshore expediant of removing one prop would not help in a loop run as the numerous locks , and perhaps marina nights require fair manuverability.