An example, not of a singer I'm afraid, but a musician.

Capt. Edward Pellew, c/o Indefatigable, organised the kidnapping of Joseph Emidy in Lisbon in 1795 to act as ships fiddler, a post held for four years. It appears Emidy replaced a previous musician. Source: the diary of James Silk Buckingham, who learned violin from Emidy. See also Dr. R. McGrady, 'Music and Musicians in 19th Century Cornwall' for more details about Emidy.