Okay, so, that tiny little upright sliver next to the flag on the stern? That's a person. On the "Large" size on Flickr, the person measures 4mm. Assuming they're 5'8" (about 172cm), the boat is 140ft long; if they're 6', it's 150ft. I didn't do all the 5'8" calculations. The tender is somewhere in the 20ft range, and the mast is around 200ft, which is why you can see it from so far inland.
Anyone else come up with a different answer?