I have been asked to fill in the details on the NT DARTMOUTH and the Atlantic speed record (see below.)
In 1985, the adventurer Richard Branson, founder of Virgin airlines, attempted a record transatlantic crossing in his power boat VIRGIN ATLANTIC CHALLENGER. The boat, capable of 50 knots left New York, and refueled at sea off Halifax, from the then IMPERIAL DARTMOUTH. The attempt failed however, when the boat sank off Land's End.
In 1986 Branson had a second try with the 72 foot VIRGIN ATLANTIC CHALLENGER II. Again he left New York and did a quick refuel from IMPERIAL DARTMOUTH off Halifax. He screamed off over the horizon at 50 knots and reached the UK in 3 days and 8 hours from New York. This time was about 2 hours better than the ss UNITED STATES record set in 1952. Branson was denied the Blue Riband however, because her refueled en route.
Ever the adventurer (now Sir Richard) Branson attempted another transatlantic speed record in 2008, this one for sailing vessels. His 99 foot VIRGIN MONEY blew out several sails only 30 hours into the trip and he instead headed for Bermuda.
To the purist, the ss UNITED STATES record will hold forever since it was set by a passenger ship in regular service. All subsequent records for powered vessels, whether recognized or not, have been set by high speed catamarans on delivery trips, and although impressive, were not in the spirit of the Blue Riband.