Short answers, pulled from the story.
A merchant ship, also called a merchant vessel, trading vessel, or merchantman, is a watercraft that transports cargo or carries passengers for hire. This sets it apart from pleasure craft used for personal recreation and naval ships used for military purposes.
A flag of convenience is when a merchant ship operates under registration from a country other than the home of the vessel's owners. Owners choose nations such as Liberia and Panama because they have more favorable maritime laws than other countries.
The Greek merchant marine is the largest in the world. The Greek fleet accounts for some 16 per cent of the world's tonnage, making it currently the largest single international merchant fleet in the world, though not the largest in history.
The UNCTAD review of maritime transport categorizes ships as oil tankers, bulk and combination carriers, general cargo ships, container ships, and other ships. The other category includes gas carriers, chemical tankers, reefers, offshore supply vessels, tugs, dredgers, cruise ships, and ferries.
The FSO Knock Nevis was the largest vessel in the world, a ULCC supertanker formerly known as Jahre Viking and Seawise Giant. It had a deadweight of 565,000 metric tons and a length of about 458 metres.
Tankers transport liquids in bulk, including hydrocarbon products such as oil, LPG, and LNG, chemicals such as ammonia, chlorine, and styrene monomer, fresh water, and wine. Special tanker types include chemical tankers, oil tankers, and gas carriers.