A master mariner is a licensed mariner who holds the highest grade of seafarer qualification; namely, an unlimited master's license. Such a license is labelled unlimited because it has no limits on the tonnage, power, or geographic location of the vessel that the holder of the license is allowed to serve upon. A master mariner would therefore be allowed to serve as the master of a merchant ship of any size, of any type, operating anywhere in the world, and it reflects the highest level of professional qualification amongst mariners and deck officers.
The term master mariner has been in use at least since the 13th century, reflecting the fact that in guild or livery company terms, such a person was a master craftsman in this specific profession (e.g., master carpenter, master blacksmith).
Norway
In Norway, the title of Master mariner (Sjøkaptein) is a protected title to which holders of a license as deck officer class 1 in accordance with the "Regulations on qualifications and certificates for seafarers" have the exclusive right. The license is the highest qualification document issued to deck officers.
Poland
In Poland, a Master mariner of great shipping (Kapitan żeglugi wielkiej) is the commander of a merchant vessel without restrictions to its tonnage engaged in great (international) shipping.
To be licensed as a Master mariner, the candidate must be: Either a licensed senior deck officer on ships of 3000 GRT and over, with an additional 12 months' sea practice of as a senior deck officer on commercial seagoing vessels of 3000 GRT and above in international shipping Or a licensed master of ships of 500 to 3000 GRT, with an additional 6 months' sea practice as a senior deck officer on commercial seagoing vessels of 3000 GRT and above in international shipping. And pass an qualifying exam as Master mariner of great shipping.
United Kingdom
The Extra Master's qualification (issued only in the United Kingdom), which was discontinued in the 1990s, used to be the highest professional qualification and it was the pinnacle for any mariner to achieve. There are also various other levels of master's certificates, which may be restricted or limited to home trade/near coastal voyages and/or by gross tonnage. The holder of a restricted master's certificate is not referred to as a "master mariner".
In the British Merchant Navy a master mariner who has sailed in command of an ocean-going merchant ship will be titled captain. A professional seafarer who holds a restricted or limited master's certificate who has sailed in command of a ship (i.e. appropriate to the size, power or geographic limits of their certificate) can also be titled captain.
In the UK, an unrestricted master's certificate is colloquially called a "master's ticket" or a "master's." It is sometimes still referred to as a "Class 1" or "Master Foreign-Going" as it was named during the latter part of the 20th century. The conventions or acts governing the certificate have evolved alongside the shipping industry and the official name of a master mariner's qualification has varied over the years. The UK Maritime & Coastguard Agency, in line with the amended STCW convention, currently title the certificate Master Unlimited.
The qualification is awarded to those senior ships officers whose competency has been assessed under the STCW A-II/2 syllabus. sac
United States
To become a master of vessels of any gross tons upon oceans in the United States, one must first accumulate at least 360 days of service (including 90 days in the most recent three years on vessels of appropriate tonnage) while holding a chief mate's license. The chief mate's license, in turn, requires at least 360 days of service (including 90 days in the most recent three years on vessels of appropriate tonnage) while holding a second mate's license, passing a battery of examinations, and approximately 13 weeks of classes. Similarly, one must have worked as a third mate for 360 days (including 90 days in the most recent three years on vessels of appropriate tonnage) to have become a second mate.
There are two methods to attain an unlimited third mate's license in the United States: to attend a specialized training institution, or to accumulate "sea time" and take a series of training classes and examinations.