Which of course is the American usage of the word "yacht" which means motor boat, as opposed to "sail boat" which means yacht. Two nations divided by a common language.
In recent years Southampton has expanded as a centre for super yacht maintenance and repair. We spotted this lovely motor vessel heading up Southampton water recently.
I'm guessing it was coming to Southampton for some work, unless that is the owner has a special interest in cruising past the Fawley oil refinery, then again maybe he owns it!!