There was a proposal in the 1830s for a ship canal along the coast, outside the railway embankment, from Dublin to the asylum harbour at Kingstown. A preliminary report was provided by William Cubitt after the House of Commons Select Committee on the Dublin and Kingstown Ship Canal had reported in July 1833.
Henry E Flynn was opposed to the idea and, in his A Glance at the Question of a Ship Canal connecting the asylum harbour at Kingstown with the river Anne Liffey at Dublin &c &c &c [George Folds, Dublin 1834], dedicated to Daniel O’Connell, he wrote eloquently of the drawbacks of the proposal, which included this:
Be it remembered, that the whole coast from Ringsend to Merrion is the bathing ground for the less affluent classes of the Citizens; and hundreds get their bread by attending on and bathing the females who frequent it.
And are the patriotic Would-be’s who support a Ship Canal equally reckless of the health, the morality, and the existence of those persons? Would they have no objection to expose their mothers, wives, sisters and daughters to the immediate wanton gaze, the scoffs, the jeers, the immodest jest, the filthy exposure and indecent exhibitions which the most abandoned race of men [ie sailors] could find in their dissolute minds to perpetrate in their view, and within their hearing? And yet, all this must be the consequence of a Ship Canal in the immediate vicinity of the female baths and bathing ground along the line.
Happily, the canal was never built.
Irish waterways history 
The ship canal proposal had been doing the rounds for at least a decade previous to this. Per Murray in “Ireland’s First Railway”, the Grand Canal engaged William Jessop to look at a plan to improve the return on their docks and he came up with a ship canal proposal at a projected cost of £405,000.
A further proposal came from a James Killaly, who “proposed the embanking of a wide strip of foreshore, along which ships could sail in a dredged channel”. The Grand Canal Co petitioned Parliament in favour of this proposal also but to no avail.
Section 55 of the Dublin and Kingstown Railway Act required that no compensation could be claimed if a ship canal were to subsequently materialise along the Dublin coast – provided that said ship canal did not touch the railway.
I have been reading Murray, Bourne’s Memorial, the minutes of evidence to the Select Committee and Flynn, all but the first of which are available online. Flynn mentions plans by Jessop, Nimmo and Sir Thomas Hyde Page. Flynn’s prose is a bit difficult to follow, but it seems that Nimmo’s plan was for a canal in a straight line from Kingstown to the South Bull Wall. I wonder whether Murray may have got Killaly’s first name wrong: the DIA entry says that John designed a Dublin to Kingstown Canal. Jessop’s plan seems to have been published in 1800. I have no date for Page’s plan but Wikipedia may provide an approximate period. bjg