Correction to comment by Lesley N., 26 Nov. 99:

"Married to a Mermaid/Rule Britannia" is not called a chantey in "50 Sailors' Songs or Chanties", Compiled by Captain Frederick J. Davis RNR, "late Captain in the Mercantile Marine," and Ferris Tozer); Boosey & Co. Ltd. c. 1887.
It is called a "General Song," along with Eight Bells, Salt Horse, The Dead Horse, The Stormy Winds Do Blow, and Farewell and Adieu to You.
The other categories by Davis, the chanteys, are "Anchor Songs," Setting Sail Songs," Song for Furling Sail," "Songs for Pumping the Ship Out."