The Yacht story sounds right. Not sure how it was a farce because you could say the operation was successful. Would have definitely been surreal though because every thing that could sail across the Channel was sent across the channel to go grab those soldiers. Probably the most chaotic and well organized retreat of all time.
i can answer that question. Been a member of the Imperial War Museum here in London for a few years and I attended a symposium that was held in conjunction of a John Keegan Book(Keegan is a must read for this who want good books on either ww1 or 2) and during the Q and A Keegan described some of the boat that answered the "All Sea worthy boats to Dunkrk". The yacht was one of the more glamours boats--most of the boats were small fish vessels, long boats that went up down the cannals here in the UK and row boats. Something like 40% of the boats that answered the call were not clear to head to open seas and most who got on them were shocked to make to back to Brighty
here are some pictures of the boards that went to Dunkirk from Dover (100 miles give or take) and if you have ever taken a small craft across the channel you will understand why some consider it a farce--regardless of the fact it was nearly a complete success
here is a picture from a reuinion a few years ago--reportedly every boat you see was sent to Dunkirk
Not sure of it will be in the movie but there is an amusing Richard Attenborough movie
here is a pathe film on the evac