The flag used by the Spanish Dunkirkers

The Spanish Dunkirkers flew the ragged cross of Burgundy on their ships. I had first become familiar with this flag when I was researching a portrait of Abraham van der Hulst that showed a ship in the background with a lion on the upper stern and flying the ragged cross flag of Dunkirk. We never were able to find the motivation behind the ship with the Dunkirk flag, but there must have been some personal connection to Abraham van der Hulst. There are paintings of what may be Witte de With's fight with Michiel Doorn from circa 1640. This is another. There is a very good Van de Velde drawing reproduced in Dr. De Boer's book about Tromp and the Dunkirkers. I have not been able to find a copy online. Thanks to Andrew for pointing this out to me.