Who was the John B. that the sloop was named for? Sloop John B is a Bahamian folk song from Nassau. It's been recorded by the Kingston Trio and by The Beach Boys, but I've always wondered just who John B was. There's a DJ that uses the name now, but who was the original?

John Bethel

A 1647 colony in the Bahamas included a Welshman named John Bethel. The folk ballad of his crew is believed to have descended through the centuries into the folk song "(Wreck of the) Sloop John B."

In 1926 the original wreck of this ship was discovered in Nassau, a Bahama island near Florida. (Sloops were precarious 16-foot vessels, sailing hundreds of miles without a chart with a 5-person crew.) Poet Carl Sandburg adapted the folk lyrics into a poem, which thirty years later was recorded by The Kingston Trio.

Sorry I can't back this answer up with something more authoritative...
http://www.destinyland.net/sloop-john-b.htm

The ship's name "John B" stood for Captain John Bethel, one of the first Welsh-based settlers on Eleuthera / Bahamas. The original text of the tragic-comic song is about a two-passenger ship that got drunk and wished for a port. The sung sloop sank in 1900 near Governor's Harbor, the administrative capital of Eleuthera. The wreck was discovered in 1926 off Nassau (Bahamas) and had probably caused Sandburg to include the song in his collection.

Translated from https://de.wikipedia.org/wiki/Sloop_John_B

There appears to be a lot of ideas out there about the Sloop John B., and I have tried to select the best sites.

• The sloop John B. was built by Captain John Bethel who lived in Eleuthera, Bahamas. It is said he built the sloop in his front yard and rolled it down to the water over logs, where it was launched.
  
• One site claims that the John B. was a sponger, a boat used in the collection of sponges.
  
• The remains of the John B. are embedded in the sands of Governor's Harbour, Eleuthera, Bahamas.
  
• The song has been recorded many, many times over the years.

If interested, you can stay at the lovely Tamarind, a home built by Captain John Bethel. It is in Governor's Harbour (Eleuthera) Bahamas.
https://en.wikipedia.org/wiki/Sloop_John_B
https://boards.straightdope.com/sdmb/showthread.php?t=145896
http://www.thepirateking.com/music/sloop_john_b.htm
https://www.collinsdictionary.com/dictionary/english/sponger
https://eleutheravacationrentals.net/Unit/Details/130146
To end, here is one of the most popular versions of the song featuring th Beach Boys!
https://www.youtube.com/watch?v=09dQmeB_NgU

If you ever visit parts of Ireland or Scotland, it is probably best not to start humming the "Sloop John B".
The tune has been used for a derogatory number called "The Famine Song", which mocks the deaths of millions of Irish people in the Great Famine of the 19th Century.

Meanwhile, any lyrics to the American Civil War tune "Marching Through Georgia" are banned at football (soccer) games in Northern Ireland.

https://en.wikipedia.org/wiki/Famine_Song
https://en.wikipedia.org/wiki/Billy_Boys#Northern_Ireland