From the Boston Almanac for 1841
18 July 1841 The Britannia, the first of the large size packets of Cunard's line, arrived at East Boston in 14 days and 8 hours from Liverpool.
In comparison, the voyage of the Mary and John, which brought the first settlers to Dorchester in 1630, took about seven weeks. More on the Britannia and other steam powered ships can be found here. I found it interesting that in January 1844 the Britannia was trapped in Boston Harbor when the Harbor froze and Bostonians paid to have a seven mile channel cut through the ice so the Britannia could escape Boston Harbor and remain on schedule.