Nick, I admit I don't know all the songs you list, but the ones I recognize I generally think of as quiet songs that people might sing along with quietly if they know the song (and if that's the practice of your song circle). I also don't recognize your shanty by its name though I may know it under another name - but most shanties I have heard tend to have refrain lines and choruses that encourage people joining in and generally singing really loud - and that's fun to do. Another thing to try is to find something with the energy of a shanty and a good loud chorus that will work with a guitar and see how that goes over. I'm willing to bet it's not that they like your shanties that much better than your other songs - it's that they appreciated a chance to be part of the wave of energy that comes from a bunch of people singing together at the top of their lungs and maybe that they wanted to encourage you for trying something outside of your comfort zone and doing it well.
   JudyB