"Art" is what the artist declares it to be. But can a collector claim the same right? In this case, the yachts are part of William (Bill) I. Koch's collection of his favorite paintings, sculptures, and artifacts-an exhibit called "The Things I Love" which ran this fall-and their presence before the classically styled museum seemed at once outrageous and perfectly normal. I approached the museum from the east, motoring along Huntington Avenue-or Avenue of the Arts, as the city now calls it-amid the heady cultural atmosphere of Northeastern University, the historic Symphony Hall, and the New England Conservatory of Music. Searching the street ahead for the right-hand turn into the parking lot I didn't notice the yachts until I was nearly on top of them. I gasped. There they stood, heeling at a gravity-defying 15 degrees, the mast of each raking the sky far above the museum's roofline. I had to put some distance between this scene and myself.