Merchant Seamen records

[urnert]

How can I find more detail on Henry Martin Leman's time as a merchant seaman (see attached). We know that he married in Victoria, Australia in 1854.

[seaweed]

No central records of Merchant Seamen were kept between 1857 and 1913. The Board of Trade in its wisdom decided that information recorded in Crew Agreements and Logbooks would be sufficient.
You need to find out the last ship he sailed on and then attempt to trace him back via Crew Agreements. Not easy.
Find my Past has some records.If it was recorded, can you post the rest of the information his ticket. You may be able to find his early ships and there may be a pattern as to what port/s he sailed from and returned to.

[Dyingout]

I remember transcribing reams and reams of these for A******* a few years back they should be searchable by name

[urnert]

Henry's ticket was issued in 1846. A contact said the last record of a voyage for him is a return to England in 1848, but  they can't remember where they found that detail. I found his ticket on Findmypast. Ancestry does not have the very early records.

[seaweed]

Dyingout. Are you sure? The  Third Register of Merchant Seamen 1853 - 1857 did record some details. Maybe these are what you transcribed.  As far as I am aware  between late 1857 and 1913, no records were kept. So they could not have been transcribed.
https://www.nationalarchives.gov.uk/help-with-your-research/research-guides/merchant-seamen-serving-up-to-1913/ 
It may pay the O/P to look at Census records to see if he was recorded on a ship in port.  There was a specific index (England and Wales  for 1861 1881 and 1901) Also take a Look at records for the Royal Naval Reserve.
An outside bet. See if he is in online 1881 Crew Agreements.
https://www.mun.ca/mha/1881/crews1881.php