There are four series of Registers of Seamen (BT 120, BT 112, BT 113 and BT 116) and it is worth coming to The National Archives to consult these on microfilm.

They give age and place of birth, sometimes a description and cross-references to the crew lists in BT 98.

Merchant seamen: Registers of service, 1835-1857

My Ancestor was a Merchant Seaman, Second Edition, Christopher T. Watts and Michael J. Watts (Society of Genealogists)