I probably first heard "Fareweel to Tarwathie" from Brian Kelly as this song was played frequently in the Idle Fellows, my part generally being in providing a penny whistle accompaniment. I vividly remember hearing Judy Collins singing it most beautifully on Wally Whyton's Folk Music programme sometime in 1983.
I still sing this very beautiful and haunting Scottish sea song myself and in the past (1998) accompanied Steffi Lubrich, who you can hear on the MP3 link above, with my concertina.

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Since writing the above in the late 1990's I have recently (August 2013) had the good fortune to have been invited to the 2nd Leserpromenade. There I sang this song on the Schulschiff Deutschland along with Off to Sea Once More and Whaling in Greenland to provide a musical background to the reading of Moby Dick by Egbert Heiß. A most enjoyable occasion!
In researching this song for the event, I learned that the text was written by the Scottish poet, George Scroggie, and published in his The Peasants Lyre in 1857. It is generally sung to the Scottish tune entitled Kennet's Dream. The version I sing has the same lyrics given in the lyric link above has just 5 verses that have been selected from the 16 verses written originally by the poet given in this link.
This song may be found in the Tyneside Maritime Chorus songbook

Lyrics