The melody is very similar to the fife tune of the same name, and both date allegedly to the mid-19th century. It may be a chantey or perhaps just a sea song. Going by the succession of place names, it describes the end of a sea voyage as the ship passes the tip of Ireland, then heading through the Irish Sea around the northwestern tip of Wales to Liverpool. Clear Island or Cape Clear Island (officially known by its Irish name: Cléire) lies south-west of County Cork in Ireland. It is the southernmost inhabited part of Ireland. Holyhead is the largest town in the county of Isle of Anglesey in Wales. It is a major Sea port serving Ireland. Fort Perch Rock is a former defense installation situated at the mouth of Liverpool Bay in New Brighton. It was built in the 1820s to defend the Port of Liverpool. The "long tail" refers to the braided ponytail worn by 19th century sailors. The line is sometimes sung as "long tailed sailor man". I think my knowledge of this song goes all the way back to the Chad Mitchell Trio in the early 1960s.