Taff or Taffy is a general nickname for Welshmen, after the River Taff and surrounding area. Maybe there were just a lot of Welshmen on those particular ships.

That may have been true of the "Minerva" as HRH Charles, the Prince of Wales was aboard. However we are talking about five or six ships which visited Portsmouth NH, (USA) and all used the "Taff" appelation.
When I visited the Medway area in UK I heard the term used frequently in relation to seamen in the Royal Navy.
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