Here is a table showing (in metres) the dimensions of locks on the Shannon Navigation.
|Lock||Width||Mitre to mitre||Mitre to sill||RL upr sill OD||RL lwr sill OD|
|Clarendon, Boyle Water||9.14||33.53||31.09||42.36||41.18|
|Drumshanbo, Lough Allen Canal||4.50||26.70||21.00||48.16||46.48|
|Drumleague, Lough Allen Canal||4.22||20.52||19.68||48.16||45.11|
|Battlebridge, Lough Allen Canal||4.11||23.16||22.45||45.04||41.07|
|Albert, Jamestown Canal||9.14||33.53||31.09||41.07||39.31|
|Richmond Harbour, Royal Canal||—||—||—||—||38.28|
I don’t know the provenance of these figures: I suspect that they were measured, or derived from plans, during the late twentieth century, but before the River Suck was made navigable to Ballinasloe: the table does not include figures for Pollboy Lock.
A handwritten note says that 2.71m should be subtracted from the sill heights to give Malin OD. These figures should not be used for navigation.
Note the interesting figures for Drumshanbo and Drumleague: Drumshanbo is a double-acting lock, capable of being used whether the level of Lough Allen is above or below that of the canal. The extra gates may explain the low proportion of usable (mitre to sill) to full (mitre to mitre) length.