1161: ’Fantastical Ships’ seen in Galway Dun
In the year 1161, fantastic and diabolical ships were seen in the harbor of Galway Dun, Ireland, to sail against the wind... and on the following day, Galway Dun was in flames.
The above account comes from a book written in 1684 by Roderic O'Flaherty [1629-1716 (or 1718)], Irish historian; so the earliest I've traced this account is still over five hundred years after it would have happened. For this reason I'm marking this account as 'unreliable' for the time being, but will continue to dig for ealier sources.
Oh, and one more quick note: in 1846, James Hardiman published an edited translation of O'Flaherty's work in which he pointed out that while the word that O'Flaherty used to described the boats was usually translated as simply 'fantastic', it also has overtones of the idea of being "devlish or diabolical"... hence my description above.