Even if he were under sail, he can not move into a collision path with another ship. Something the rag and stick brigade seem to forget.
Additionally, the big ship is probably limited in manouverability, and has right of way over the sail boat.
However, as the sailboat was under power, he was not showing the correct signals to show he was under power, and then, whilst under power turned to cause a collision.
No question on this one.
If you want to see this again, go to the Solent in August.