Thanks for your comments... the frank ones are quite often the ones you learn most from!
The posts are part of a shipwreck. While on one hand I guess a different angle may make that more apparent, their function was to lead the eye into the picture, so personally I'm not sure how important it is that they are identifiable? Be interested in peoples thoughts on that.
You're right mud isn't an appealing thing per se but I find the channels and ripples the water carves into it can make some interesting shapes... but it's all I have to work with at the moment, that's all there is on my nearest bit of coastline. I do intend to travel a bit further afield but thought I'd practice my technique locally first.
WB may be down to me needing to calibrate my monitor. I've tried doing it with the apple built in one but I need to invest in some proper software with a meter rather than something that involves me squinting at the screen!