With my John Edmonds there is no doubt he was a master MAriner
I have several ships quarterly returns (from Sussex record office) and crew lists for ships he sailed - and he is clearly recorded as the Master of the ships.
From as early as 1774 masters or owners of merchant ships were requird to keep Muster Rolls giving deatils of the crew. But following the 1835 Merchant Shipping Act the Master of every ship over 80 tons was required to send to the Regostrar of Shipping the written agreement of every member of the crew, laying down wages, voyages to be made, duties of the crew, and provisions ot be provided. The Master was also required to make a return every half year to the Shipping Master at the home port (in my case Littlehampton) giving details of voyages made in the prevuoos 6 months, crew employed, etc.
These had to be filed within 21 days of end of June and Dec.
Now, few of these have survived and what have are scattered and difficult to trace. The first place to trry is the Local record Office, but I understand Kew and the Maritime Museum at Greenwich may be other places to try.
From 1823 all ships over 80 tons had to carry a quota of apprentices , th the same Merchant ShippingAct required Apprenticeship iondentures to be filed with the Registrar General of Shipping. Again very few of these documents survive - but you may be lucky! I have a copy of the Apprenticeship indentue entries for two ancestors who went to sea (there are several in my tree, though only one MAster mAriner) but sadly they are both annotated 'Drowned'.
Re the second of these we found out a lot about the incident from a very helpful person at Greenwich - It was a good few years ago and I think we had to make an appointment to go there rather than it being generally open, but my memory is a bit vague. But they were very helpful and found an article describing the incidnet in which the 'Remembrance' on which my rellie was acabin boy, collided with 'the Kelloe' a few miles off Flamborough Head and how they limped to shore only to discover the cabin boy was missing, so presumed to have fallen over board.
So - sorry this is long, you may not actually be interested - but the moral is to keep looking, try every everything and everywhere, and it is amazing what you can come up with! For every hundred or more ideas you follow up that get nowhere, there will be one that produces results and that make sit all worthwhile! Well, that's been the policy of my brother and I over about 15 years!