Hamish, good on you for taking all the comments in the spirit in which they were intended. It is good to experiment with new ideas and techniques - sometimes the results work, sometimes not, but experimentation will ultimately make you a better at both photography and post-processing (I really should take some of my own medicine....). All that said, you have some wonderful photos in your portfolio; Pensive is gorgeous!
Not a fan of the desat effect you used, to me it would have looked nicer to leave the water and sky normal. I also noticed there is some of the desat layer that did not get removed around the ship which just makes the sky look dirty. Overall I do however like the composition of the shot wtih the ship framed by the chain and post.
I really like the concept. i would like to see what the effect would have been if the whole sky had be left in color and only the pier and chain were in duotone.
I find this almost bizarre, and visually confusing. The partial desat gives the appearance of a hoarding, rather than a real scene(which may of course, have been part of your intent). It is an interesting idea, but for me doesn't work on an aesthetic level, coming across as somewhat gimicky. On a technical level, there appears to be a masking error at the third-fourth link in from the left, although looking again it may be part of one of the clouds.
This would've done much better if it were all in color and not done this way. You can see the obvious parts you missed when using the layer mask...going for brown?
The selective desat and sepia do a nice job of directing attention to the ship. At the same time, they give the photo a somewhat claustrophobic feeling ... like the world is closing in on the ship. Maybe the ship represents freedom or escape from the darker more pressing world. Lots to think about here.