This is a table showing (in metres) the sizes of the locks on the Limerick Navigation, the now-abandoned link between Limerick and Killaloe. Cussane, Errina and Gillogue were double locks (staircase pairs).
|Lock||Width||Mitre to mitre||Mitre to sill||RL upr sill OD||RL lwr sill OD|
|Abbey (sea lock)||6.40||39.32||38.25||3.30||1.62|
Killaloe, Moys and Cussane were on the uppermost canal section. Below that was a river section through O’Briensbridge; the next canal section ran from Errina to Plassey. The navigation then returned to (and crossed) the river before entering the final canal section, which had one lock about half way down and another at the bottom, where the canal joined the tidal Abbey River, a section of the River Shannon in Limerick.
I don’t know the provenance of these figures: I suspect that they were measured, or derived from plans, during the late twentieth century. 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 (if that were possible).
There is no mitre to sill figure for Killaloe lock. That may be because it was built as a double-acting lock: able to work whether the level of Lough Derg was above or below that of the canal. The level of the lake is said to have varied by up to eleven feet between winter and summer before Ardnacrusha hydroelectric power station was built in the 1920s. I do not know why there is no mitre to sill figure for Park lock, which currently has a concrete dam in it.
The tidal lock (6.40 m X 39.32 m) is much larger than the others. I don’t know whether the promoters originally intended to build the entire canal to those dimensions or whether they envisaged estuary vessels using the canal harbour above the lock. The other locks range in width from 4.62 m (Clonlara) to 5.08 m (Cussane) and in usable length from 22.56 m (Plassey) to 28.96 m (Gillogue Upper).
Cussane Lock is under water in the “flooded area” above Parteen Villa Weir but all the other locks are visible; admittedly only the top of the chamber can be seen at Moys. The tidal lock has working gates (as well as large amounts of mud outside it).