File:Lock 61 chesapeake and Ohio canal from NPS.jpg

English: Lock 61 on C and O Canal. Nps site says: Lock 61 is the third of the 13 composite locks and had a 10 lift’. These locks differ from the other locks on the canal. Between the upper end of the lower gate pockets to the lower end of the upper gate pockets the stone walls were moved 9 ¼° on each side, resulting in a clear dimension between lock walls of 16’-16 ½” rather that the 15’ previously adhered to. The normal clear dimension was resumed both up and down from these points. The walls were of rough-cut and rough-coursed limestone, principally dry-laid where the walls were widened and mortared in the other areas. The wider area was filled in with 5 ¼” square timbers. This wooden section of the lock was “water-proofed” at first by being “kyanized” and later with creosote. The wood timbers required frequent replacing, and around 1900 many repairs were made by stripping out the wood and pouring a cement liner. This was the case at Lock 61.

Shortly after its construction an extra 2’2” height of stone wall was added from the lower end of the upper gate pocket. The normal gate was 14’ high (8’rise plus 6’ prism depth), but due to the 10’ rise these locks, 16’ high gates were required. The 2’ addition to Lock 61 required and unusually high gate of 18’.

The upper berm wingwall runs perpendicular to the lock for 31’ to the inflow of the bypass flume. This long wall is buttressed at about mid-point by a thickening of 3’6” for a 3’3” distance. On the upper towpath wingwall, a 3’3” buttress is placed after a 9’ run of wall. After a straight run of 13’ the lower extension walls splay out at a 60° angle for about 15’ and the lower berm then runs for 19’, perpendicular to the lock to the outflow of the bypass flume.