A little info on the button. RNYC may refer to the now Royal Northern and Clyde Yacht Club (formed in 1978 as merger of two much older yacht clubs - The Royal Northern Yacht Club (founded 1824) and the Royal Clyde Yacht Club (founded 1856). The "royal" designation given to the RNYC was believed to be the first given to a British yachting club. You can read more here
https://en.wikipedia.org/wiki/Royal_Northern_and_Clyde_Yacht_Club
As wiki is helpful but not always accurate, further digging found some references/pictures here:
https://books.google.com/books?id=R...VCBU-Ch3_sgg0#v=onepage&q=RNYC button&f=false
Finally, as your button does not appear to have thistle tipped wreaths as many of the examples do, I'm guessing you have a variant of the typical RNYC button, a backmark ID may help narrow things (many were made by two british firms: Armfield is one, Gaunt is another) as well as nail down age. Guess from other finds you made close to the button as well as the feeble depth of research ive devoted to it, i'd say last quarter of the 19th century.
Cool find!
-H