A curtal sonnet is an eleven-line sonnet that was invented by Gerard Manley Hopkins. It follows a rhyme scheme of abcabc dcbdc or abcabc dbcdc. It has features that are similar to the most common sonnet forms, the Petrarchan and Shakespearean, but it’s also distinctly different. The poem consists of 10 lines written in iambic pentameter and a final line consisting of a single spondee (or foot consisting of two long or stressed syllables). Here’s the rhyme scheme:
Line 1: a
Line 2: b
Line 3: c
Line 4: a
Line 5: b
Line 6: c
Line 7: d
Line 8: b
Line 9: c
Line 10: d
Line 11: c
I admit I am rubbish at metre. I read it back and if it sounds right I am ok with it.
GMH most famous example is Pied Beauty
https://www.poetryfoundation.org/poems/44399/pied-beauty
Online Links
https://www.writersdigest.com/write-better-poetry/curtal-sonnet-poetic-form
The Wombwell Rainbow 