A model for a Canal Lock of a very ingenious and curious construction, has lately been presented to the Company of Undertakers of the Grand Canal, by an artist in this city [Dublin], having among some other improvements on the old locks the following remarkable ones:
- That of raising or falling a boat from a level of sixty feet by a single lock.
- That of obviating, by a single contrivance, the waste of water, so that at the passage of any boat through it, more than nine-tenths of the water will be retained for the next occasion: this lock will therefore not require a sixth part of the water now expended in the smallest lock on the navigation.
The model is now in complete order at the Navigation House, and was particularly intended by the inventor to answer the great fall from the level of the Canal at James’s-street to the river Liffey; an object not yet fully determined upon by the Company, which Company has, however, as a token of its approbation of so very ingenious a contrivance, presented the inventor with twenty guineas, and should his plan be ever executed by them, there is no doubt but he will be rewarded according to his merit.
Saunders’s News-Letter
12 September 1787
Irish waterways history 
I wonder if it would have been like Fussels balance lock.
https://en.wikipedia.org/wiki/Balance_lock
Saving space (land) and water would have been helpful, I think. The Grand Canal Company eventually decided to take a different route from their harbour to the Liffey, going around the south of the city instead. The original idea, of a direct link north to the Liffey [about which I’ll have more shortly], faced the problem of getting downhill in a short distance. Interestingly, Messrs Guinness (stout fellows) later faced the same problem with their tramway, which had to link the upper areas of the brewery, alongside the canal harbour, with those alongside the Liffey and with the mainline railway and their quay. They used a spiral tunnel …. bjg