I have been playing this game, too.I think you may have nailed it there Wrecker, I was thinking Boar War, anyone know when the R. F. A. went over to the Blue Ensign.
Not saying it is the Maine as I can't find any photos of her from astern that were taken at the time, it was the only one(so far) with the right mast/funnel arrangement carrying enough boats.I have been playing this game, too.
However I'm not sure @WreckerL is correct. The ship in the OP has a square, transom stern. with yet another ship's boat on davits over. Neither are apparent in Wreck's post.
Not that I have yet come up with anything better.... I did look at a number of past Royal Yachts, but none have that many boats, and the funnel is ( I would have hoped) too dirty for a RY.