"That could have happened regardless of who was driving, if or not they were drunk..."
But it would not have happened had he not taken to the water when, by all accounts, both of them were considerably the worse for wear. It was his boat and he had access to it. Miss Brown did not initiate the event and that's where the negligence began.
This really demonstrates that it is usually unwise to take issue with decisions made in criminal courts. A lengthy trial was held which exposed the facts before a jury. We read a few snippets in the papers and think we have the whole story. We don't, as both this and the David Duckenfield case demonstrate.
Apparently Mr Shepherd's appeal will centre around the fact that he did not receive a fair trial and the judge misdirected the jury. Of course if he had been there he might have been able to avoid that.