After a suggestion from Marell on the Sea of Claws Man O'War group I've added a lot more white foam to the waves where they hit the rocks. I've also added some clump foliage as bushes to the land, leaving the area around the castle mostly clear.
Here are a few photos. First off the castle and beach...
Then with some Dwarves and Empire ships on the sea boards and the small islands I had before.
Hmmm... I may have to do another bit of coastline... Perhaps with a harbour.