To WOW/Rodward (drifting leewardly?)
In reply to:

Taff as nautical nickname for UK sailors
Taff or Taffy is a general nickname for Welshman, after the River Taff


Let's start w/ some additional info (facts?) and then segue quickly to some speculative faux- folk etymology seeking to link Ancient St. David, (7th Cent) the patron saint of Wales, to some latter day Welsh Mariners. First, some "facts" from my paper (no "goo-gooing around) copy of The Facts On File Dictionary Of First Names, quoting randomly from the entry "David"( which, not co-incidentally, happens to be my own "first" name.)
"Saint David (7th c.) became the patron saint of Wales and caused the name to be intensively used there at all times thereafter. ....Pet forms include Welsh Taffy, Dai, Davy". For "Taffy", cf. "Taffy was a Welshman, Taffy was a thief," etc.(and maybe a sailor as well?) And now for our faux-etymology. It seems a logical line from >St David > ST Davy >St Davy's Day> (and note, e.g. S's humourous treatment of Welsh accents w/ Fluellen in HenV -"P"s for "B"s and other mistaken initial consonants >Sint Davvy's Day and then an elided "D' replaced by the final "t" of Saint to arrive at "St Tavvy" and finally, but easily, logically, "Taffy". Query, which came first, "River Taff" or "Taffy" from the ancient, good St David. Who knows or cares, but that's why we have these discussions - a few facts twisted about w/ a bit of speculation seeking to answer some unanswerable Qs. We personify our breeds of warriors. ("Johnny" marching home from WWI and "GI Joe" in a foxhole in WWII. Perhaps a large number of Welsh sailors became, generically, "Taffies" during those centuries when (as even now?) Brittania ruled the waves. Now,( carefully replacing my paper volume to its familiar place) I shall leave it to the on-line researchers to verify or discredit my daffy etymology. ..... This is an "Edited Post" after-thought (or, as I call it, a Post-Scribble) I just remembered (about five minutes after posting the foregoing) that Shakespeare, in Hen V, has Fluellen say, somewhere, "f"alorous" meaning "v"alorous" "f" substituted for "v" as in "Davvy" becoming "Daffy" and the "t" of Saint sliding over the "D' of Davvy to become "Taffy". I don't know about you, but I have just convinced myself. .......