Steely Dan, for example, definitely made some yacht rock. The Aja album has Deacon Blues, Black Cow, and Babylon Sister and are as yachty as rock gets. But most of the Steely Dan earlier catalog is not . . . not only because the timing isn't right but the sound/style isn't right. Aja came out in 1977, when the yacht rock sound was well underway, but there's probably examples of genuine yacht rock before that. Also, I think the genuine era was short, by about 1981, the real stuff was mostly over.
BUT all this means there's ample room for debate.