Further to Frances Coakley's suggestion, you may get some information out of my cousin Captain Harry Hignett. He is the research officer for the Liverpool Nautical History Society. their website is www.Cronab@Demon.co.uk/lnrs and Harrys email address is Harry.Hignett@tesco.net  I know they have been able to help track individuals through registered shipping lists before 1820.Good luck!  John Quirk