Beards aren't a thing.
Perhaps more appropriately, I should say that beards aren't a thing sailors chose to wear, except in the most dire circumstances. In the hundreds of images I've examined, only four clearly show beards.
|Without._from the London Gazette of 11 June, 1757, T. Ewart, |
Yale University Lewis Walpole Library.
|A new way to pay the National-Debt, James Gillray, 1786, British Museum.|
|Plate from Histoire des Naufrages, engraved by Marillier, 1788, |
John Carter Brown Library of Early American Images.
|Frost on the Thames, Samuel Collings, 1788-1789, Yale Center for British Art.|
This appears to be the case in what few references there are in sailors' memoirs, too. Ebenezer Fox, writing many decades after his experiences, claimed that prisoners on the hulk Jersey had 'their beards never cut, excepting occasionally with a pair of shears, which did not improve their comeliness, though it might add to their comfort.' Despite their condition, they still sought to cut away what facial hair they could.
I've found only one case in which a sailor chose to wear a beard in this period. When John Nicol learned that a press gang awaited him back at port, 'I had allowed my beard to grow long and myself to be very dirty to be as unlikely as possible when the man-of-war boats came on board to press the crew.' He believed, perhaps rightly, that the Royal Navy had no interest in taking a dirty, bearded soul that might infect their ship. While it is likely that Nicol did more than grow a beard to appear disheveled and undesirable, it was the only specific action he relates in this goal. Nicol thought that the beard was essential to looking 'very dirty.'
Some sailors undoubtedly did wear sideburns, as depicted by Copley in his masterpiece Watson and the Shark.
|Watson and the Shark, John Singleton Copley, 1778, National Gallery of Art|
 Fox, Ebenezer, The Adventures of Ebenezer Fox in the Revolutionary War, Boston: Charles Fox, 1847, page 108.
 Nicol, John, The Life and Adventures of John Nicol, Mariner, edited by Tim Flannery, New York: Atlantic Monthly Press, 1997, page 162.
 Snell, Hannah, The Female Soldier; Or, The Surprising Life and Adventures of Hannah Snell, London: R. Walker, 1750, in The Lady Tars: The Autobiographies of Hannah Snell, Mary Lacy and Mary Anne Talbot, Tucson, Arizona: Fireship Press, 2008, page 26.