Just stumbled across this. Thought it might have a Liverpool interest.



You can now search 359,000 records of Merchant Navy Seamen for the period 1835-1857 on findmypast.co.uk (They already have 1918-1941)

The information the records hold about your ancestors can vary, but they usually include name, age, place of birth, physical description, ship names and dates of voyages.
Wow. Physical description. That would be good.