I didn't notice your post earlier. I put 'harp' for this, but that was only to fit with the theme - and also because I needed a 12th entry for the third category (the ones to be modified before entry).
Boreas, having had another look...I don't know how 13 A works, but I definitely think it is correct. (The last line in the preamble settled it for me).
Yes, I want it to be harp - but that would mean it would have to be an anagram, and so far I can't find one.
I have highlighted the answers, but can't see a shape or anything.
28 - I assumed the vessel was a tanker, topless it's an anker, a drinks measure (varying, according to Chambers, so that'd fit 'inconsistent'. I didn't get the significance, if any, of Newfoundland.