On long trading voyages the owners embarked a supercargo — their commercial agent, who outranked the master in everything to do with buying and selling the cargo. East India Company supercargoes on the Canton run handled fortunes in tea and silver and could overrule a master's choice of port. The telegraph, then steamship liner agencies with offices in every port, made the floating merchant redundant; his commercial power flowed partly back to the master and mostly ashore.
Supercargo no longer exists as a living trade. Here is what erased it, and which profession took on the work.
1450 – 1850
The age of sail and the master under God
Ocean routes to the Americas and Asia turned shipmasters into instruments of empire and commerce, employed by state-chartered giants like the Dutch and English East India companies. Ships' articles named the master "under God" as absolute authority for the voyage, with discipline to match. The tools of command sharpened fast: printed charts, Lloyd's coffee house organizing marine insurance from 1688, the sextant, and finally Harrison's chronometer, which let Cook chart the Pacific with an accuracy earlier masters could only imagine.
What else was happening then
1761
Harrison's chronometer solves longitude
On its trial voyage to Jamaica, John Harrison's H4 marine timekeeper lost only seconds over 81 days at sea, finally letting a master fix longitude from the deck of a moving ship. James Cook carried Larcum Kendall's K1 copy on his second Pacific voyage and called it "our trusty friend the watch" — position-finding passed from educated guesswork to instrument reading.
1876
The Plimsoll line limits the master's cargo
After Samuel Plimsoll's parliamentary campaign against overloaded, over-insured "coffin ships" that drowned crews for their owners' profit, Britain's Merchant Shipping Act of 1876 forced a load line onto every hull. For the first time, a painted mark on the ship's side — not the owner's ambition — set the legal limit on what a master could be ordered to carry.
1912–14
Titanic sinks; SOLAS is born
The loss of the Titanic and some 1,500 people under Captain Edward Smith in April 1912 exposed how far ship size had outrun safety law: lifeboat capacity was set by tonnage, not by people aboard. The first International Convention for the Safety of Life at Sea followed in 1914, requiring lifeboats for all, continuous radio watch and an ice patrol — the treaty that still governs a master's safety duties today.
Where that work lives now
The last absolute command: one licensed master answerable for ship, crew and cargo, from Zheng He's treasure fleets to today's container giants.
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