Saw it some years ago but can’t find it now using Google Images. It’s from the late 1800s or early 1900s, I believe; looks like it might be by John Singer Sargent but I don’t think it actually is.
Could it be Regattas at Molesey by Alfred Sisely?
No, but thanks - the one I have in mind shows some folks lounging on the deck of the yacht, with the flags overhead. The brushwork is much more precise than Sisely’s.
Ball on Shipboard, by James Tissot?
Hmm. That looks very much like it, although I remembered there being fewer people, and the brushwork had more of an Impressionist feel to it. May I ask how you knew of that painting?
Prof. Pepperwinkle used Tissot in a Botticelli game a few months ago. 
Look for paintings by Bernard Finnigan Gribble. He was born in the 1870s and lived into the 1960s and spent his life painting mostly maritime scenes. From what I’ve seen of his work it has a blurry style that reminds me of impressionism.
Thanks. I checked Gribble on Google Images and came up with nothing like I was thinking of, but did find this great World War I destroyer picture, “The Return of the Mayflower,” I remember from many years ago. It is (or has been) displayed at the Pentagon in the office suite of the Secretary of the Navy: http://herreshoff.org/programs/lecture_series_67_3034456882.jpg
Franklin D. Roosevelt was the original buyer of this painting and he’s the one who came up with the name according to Wikipedia. The painting was in the White House when FDR was president. I just recently learned of this painting and the artist when it was mentioned in Erik Larson’s book Dead Wake about the sinking of the Lusitania. The painting commemorates the arrival of the first U.S. Navy ships to combat the Germans’ U-boats.