I did the course ,Short Range Cert Modules 1&2 with DMG Sailsports in Malahide, great course very well run, it took one evening from from 19.30-10pm, and then one full day from 9-16.30pm, then the exam written and aural straight after the course. Its a long day but once you've passed it you have it for life. It cost me E250 all in including the cert, but shop around, you might get it a bit cheaper elsewhere. when you get your cert you can then apply to Comreg who will issue you a ships radio licence
for E100, they then pass your boats info eg. size, max people etc onto the coasgaurd etc, who then have most of the info they need in the event that you make a distress call. Its not a requirement to have , but what price safety, no point sayin' should've done it, when yer up to your neck in water like!
