According to the Irish Times of 11 February 2017
Margaret Gaffney was born on Christmas Day 1813, in Tully, Co Leitrim. Five years later, faced with extreme poverty and religious persecution, her parents and the three youngest of their six children, including Margaret, boarded a steamer bound for Boston.
Eoin Butler, the author of the article, provides no details of the vessel, but I hope he will: up to now folk have believed that an American vessel called the Savannah was the first to use steam on any part of the Atlantic crossing, and that was in 1819, the year after Margaret Gaffney’s crossing.
Irish waterways history 