Thanks Len, for your help. Am not sure - the Isle of Man to Cornwall via Whitehaven certainly seems a possibility esp for "a mariner".
Have come across John Blake before and put him into "for reference" file as he wasnt in Penzance and Melicent joined the other names in this group which dont appear in my family (except for William).
Am still thinking it through - thanks very much for your help. If you come across anyone from the Isle of Man in Penzance - let me know?!