As Mike T. correctly speculated, the sloop yacht M.S. Quay was almost certainly named for the famous Pennsylvania senator Matthew Stanley Quay. A Sept. 6, 1895 article in The Press of Atlantic City has the vessel owned by Captain Ben Sooy, and at the disposal of the senator for a fishing trip to Florida. Other articles show that Sooy, described as a "piscatorial expert", was regularly a fishing guide for the senator.

Matthew Stanley Quay was a U.S. senator from Pennsylvania from 1887 to 1899 and 1901 to 1904, when he died. According to Wikipedia, "Quay's control of the Pennsylvania Republican political machine for almost twenty years made him one of the most powerful and influential politicians in the country." There is a public park named after him in his hometown of Dillsburg, Pa.

It seems likely that this yacht would be named for someone so well-known, but I haven't been able to find any evidence to prove it ...

[That M.S. is -- possibly -- an abbreviation for "Motor Ship." - Dave]

Edit: Thanks for the info, Dave. Shows how much I know about yachting.

[Update: You were right! - Dave]

Utah became the 45th state in 1896. The 44 star flag, after Wyoming in 1890, had the top and bottom rows with 8 stars and the middle four rows with 7 each, which looked more boxy. This photo being made in 1905 should have had the 45 star flag which had the 1st, 3rd and 5th row with 8 stars and the 2nd, 4th and 6th with 7. I think the 8th star on the top row is hidden behind a fold in the flag at its top right corner.

[Just because it's 1905 doesn't mean you have a 1905 flag. Especially when the flag kept changing every few years. - Dave]

So elegant and handled with ease ... we need more of these yachts around. Of course, before the advent of modern sail material, canvas sails would require a lot of care and storage in lofts. Every school child in coastal areas need to learn sailing to build a spirit of adventure, maturity, and an appreciation of doing difficult things. Also, bring back the old yachts for the America's Cup. Teak and mahogany are more romantic that carbon fiber foil boats that only tack a few times.

Nice pattern of the 46 stars on the on the flag. A clever person figured it out . Arizona and New Mexico in 1912 changed it to 48. Not many of the 46 star flags around today.

[The flag has 44 stars, not 46. Oklahoma became the 46th state in 1907. - Dave]