The maximum length of barge allowed to navigate through the French canal system is slightly longer than the official length of 38.50m indicated throughout the Practical Navigation pages on this site.
The Belgian owner of a 39.12m long barge asked if his barge could squeeze into the locks to reach his planned destination on the Mediterranean Sea in 2017. Research revealed that the 38.50m standard was established in the days of towing on the canal towpaths, first by horses and later by ‘electric mules’. When barges were fitted with engines, this meant adding a propeller casing and a more substantial rudder. Hence the extra 65 cm.
So while the 39.15m barge can make it through the system, it means using every bit of margin available within the lock chamber, and it literally means ‘squeezing in’, and being extra careful not to snag on the upstream gate sill, nor to touch the downstream gates when rising in the lock.