I don’t know how the poor benighted foreigners cope with the organisation of Irish government departments. In fact, I don’t even know how poor benighted Irish folk cope with it.
Let us assume that you want to find out stuff about Irish policy on ships. Fortunately, you find www.gov.ie, and select Government departments. And there, on the very first line, is what you want: the Department of Agriculture, Food and the Marine. So you troll on over there, and if you’re very lucky you’ll select Fisheries, because if you do that you may realise that the only marine thing in the Dept of Ag is fish. And only sea fish: freshwater fish are the responsibility of a body called Inland Fisheries Ireland (surely that habit of calling things “such-and-such ireland” should have died off by now), which reports to the Department of Communications, Energy and Natural Resources.
So where are the ships? They’re in the Department of Transport, Tourism and Sport, under Maritime. And some day they’ll reorganise their section of the website so that things can be found easily. But inland waterways come under the Department of Arts, Heritage and the Gaeltacht.