Just North of Ile de Yeu I was stooging along minding my own business. Ahead of me , coming my way was a strange commercial craft, seemingly meandering with no purpose. I turned on the radar to make sense of him, to no avail. However, when he got about half a mile away, just when I was getting concerned he shot off to his stbd (my left) and joined up with a large motor launch which had been hanging around. I am sure he had not seen me.