Hi Laurence,
Your experiments show real promise and they look realistic. The color is dead bang on and you've nailed the shapes. As Paul mentioned there needs to be some translucency here and there. As I have never attempted violent ocean water, only still seawater by a dry dock and canal water, I wouldn't presume to give you advice. However, I know a guy in New Orleans who has done that, I believe using some kind of resin within the Celluclay to simulate the translucent areas. I remember being impressed with his method. I'll email him and see if he will let me in on his secret!
I like the way you work. Experiment with something other than the subject, so if it goes wrong, nothing is lost. It's great to see guys pushing their limits! I've been pushing mine in so many directions for so many years, but it seems the more I learn, the more I need to learn. It's an endless process.
Bob