Who on earth red blobbed me for mentioning Brendan the Navigator?
The theory that Brendan may have completed this voyage is taken seriously ...so much so that Tim Severin completed a successful re run to prove it was very possibly true.
Have a look : http://www.castletown.com/brendan.htm
And several other references on that Googlepage.
It's not even controversial!!! Someone out there's very sad...