Locaboat tells us that
All the countries of Europe have agreed to facilitate access to hire-boats which are duly equipped and certified, and operate in tourist areas where there is little commercial shopping [presumably “shipping”].
In France, Germany [list of areas], Ireland, Holland, Poland and the Venice Lagoon Locaboat has received permission from the local authorities for their boats to be hired without licence. Initial instruction, both theoretical and practical, is given at the point of embarkation, enabling you to quickly master your boat and grasp the essential rules of navigation. You will then be given a licence that is valid for the duration of your stay.
When you’re starting from Ketzin in Germany, however, a boating licence is obligatory. This is not valid for citizens from countries that don’t have a boating license (e.g. Great Britain or Denmark).
This suggests that Ireland does have a boating licence, which is the first I’ve heard of it.
On its English-language front page, incidentally, Locaboat bigs up the fact that licences are not required in Poland:
Licence free hiring now also in Poland
Good news: Due to a new regulation, since 1st August 2010 a boating license is no longer required for our boats in Poland! Now a barge trip in the natural paradise of the Masurian Lake District becomes even more attractive.
And very nice it looks too. I wonder whether the Polish lakes have provided extra competition for the Irish.