Maritime Transport and How It Works
The units that measure sea trade, UNCTAD data, liner and tramp shipping, ship types, cost structure, chokepoints and the regulators.
Maritime transport is the carriage of cargo and passengers by ship, and it handles more than 80% of world merchandise trade by volume.[1] UNCTAD's latest full-year figure puts seaborne cargo at 12.72 billion tons in 2024. The industry divides by operating model into liner and tramp services, and by ship type into bulk carriers, tankers, container ships, general cargo, ro-ro and gas carriers. Its rules come largely from IMO conventions, applied through flag state and port state control.
Measuring the Market
Two units describe seaborne trade. Tons record how much cargo moved. Ton-miles multiply cargo by distance, giving a better measure of demand for ships, because the same cargo sent further keeps a vessel occupied for longer.
A simple illustration: 100,000 tons carried 8,000 nautical miles comes to 800 million ton-miles. Send the same cargo 11,000 miles and the figure rises to 1.1 billion, an increase of 37.5% with no extra cargo at all.
The 2024 numbers show this clearly. Volume grew 2.2% to 12.72 billion tons, whereas ton-miles rose 5.9% to 66,781 billion, the fastest growth since 2011. UNCTAD attributes the gap mainly to the diversion of ships from the Red Sea around the Cape of Good Hope and, to a lesser extent, to Panama Canal restrictions that lasted until mid-2024.[2] It projected growth of 0.5% for 2025 and an average of 2% a year for 2026 to 2030.[2]
As for supply, on 1 January 2026 the world's roughly 116,000 commercial ships of 100 gross tons and above had a combined capacity of about 2.5 billion dwt. Oil tankers and bulk carriers accounted for 69% of that total.[3]
Liner and Tramp Shipping
The first division is operational. A liner service calls at advertised ports on a published schedule and sails on its date however full it is. Container lines and ferries work this way. Shippers buy space at tariff rates or under annual contracts, and the bill of lading is the transport document.
A tramp has no timetable and goes where the cargo is. A vessel might load wheat in the Black Sea, discharge in Egypt and then look for its next employment on another coast. Most bulk carriers and tankers trade like this, fixed by voyage or by period under a charter party. Prices form on the spot market and are followed through benchmarks like the Baltic Dry Index. The freight guide explains how the rates are built.
| Feature | Liner | Tramp |
|---|---|---|
| Schedule | Published | Set by the cargo |
| Cargo | Small parcels from many shippers | One or a few large parcels |
| Pricing | Tariff and annual contract | Spot negotiation, period charter |
| Document | Bill of lading | Charter party and bill of lading |
| Typical ship | Container ship, ferry | Bulk carrier, tanker |
Main Ship Types
Cargo ships are designed around what they carry, which decides the shape of the holds, the tank layout, the handling gear and the speed.
| Type | Cargo | Key feature |
|---|---|---|
| Bulk carrier | Ore, coal, grain | Size classes from Handysize to Capesize, mostly tramp |
| Tanker | Crude, products, chemicals | Segregated tanks, pumps and pipework |
| Gas carrier | LNG, LPG | Pressurised or refrigerated tanks |
| Container ship | Standard boxes | Cellular holds, almost entirely liner |
| Multipurpose and general cargo | Breakbulk, project cargo | Own cranes, wide hatches |
| Ro-ro and car carrier | Wheeled cargo, cars | Loading by ramp |
| Reefer | Fruit, meat, fish | Temperature-controlled holds |
Non-cargo vessels are part of the system as well: tugs, pilot boats, cable layers and offshore support craft. The small tankers and barges that deliver fuel to ships in port form the last link in the bunker supply chain.
The Cost Structure of a Ship
Ship costs fall under three headings. Capital costs come from buying and financing the vessel. Operating costs cover crew, maintenance, insurance and stores. Voyage costs consist of fuel, port charges and canal dues.
The contract decides who bears which. Under a voyage charter the owner pays everything and recovers it through freight. Under a time charter the charterer pays fuel and port costs, and the daily hire covers the owner's operating and capital expenses. On a bareboat charter the charterer also supplies the crew and runs the ship. Since fuel is one of the largest voyage costs, the type of fuel and the choice of speed feed directly into the economics.
Chokepoints and Rerouting
Seaborne trade funnels through a small number of narrow passages, chief among them the Suez Canal, the Panama Canal, the Strait of Malacca, the Strait of Hormuz and the Turkish Straits. Closing or restricting one does not remove the cargo. It lengthens the route, which raises demand for ships, as the 2024 ton-mile figures show.[2] A longer route also means more ship days and more fuel burned, and both reach freight rates and bunker demand.
Regulatory Framework
A ship answers first to its flag state, which registers it, issues certificates and oversees it. International standards come mostly through IMO conventions: SOLAS for safety of life, MARPOL for pollution, STCW for training. The ILO's Maritime Labour Convention 2006 sets seafarers' working conditions. In port, foreign vessels are subject to port state control. Domestic carriage is usually reserved for the national flag, a practice called cabotage.
Environmental Footprint
Per tonne-kilometre, ships emit less carbon than trucks or aircraft, which is one reason long-distance trade goes by sea. The total is still large. The Fourth IMO GHG Study puts emissions from international, domestic and fishing vessels at 1,076 million tonnes of CO₂ equivalent in 2018, and their share of global anthropogenic emissions rose from 2.76% in 2012 to 2.89% in 2018.[4] On sulphur, the major step was the 0.50% global limit that took effect in 2020.
The Main Parties
Moving cargo by sea takes a chain of parties, and contracts use these terms in specific senses. The owner of a ship may not be its operator, and the operator may not be the party that finds the cargo.
| Party | Role |
|---|---|
| Shipowner | Owns the ship or operates it commercially |
| Ship manager | Provides technical management, crew and maintenance |
| Charterer | Hires the ship for a voyage or a period |
| Shipper and consignee | Sale parties, tied by an Incoterms rule |
| Port agent | Handles port formalities for the ship |
| Shipbroker | Brings ships and cargo interests together for charters |
| Freight forwarder | Organises transport on behalf of the cargo owner |
| Classification society | Surveys technical standards |
| P&I club | Insures liability to third parties |
The Incoterms rule in the sale contract decides who books the ship. Classification societies and P&I clubs stand outside the commercial deal and provide the assurance a ship needs to trade.
Core Transport Documents
The bill of lading has three functions: a receipt for the cargo, evidence of the contract of carriage and a document of title, which allows cargo to be sold during the voyage by transferring the bill. The charter party is the contract for hiring the ship. On a voyage charter it records laytime, demurrage and freight, and on a time charter the period, daily hire and guarantees of speed and consumption.
Both can appear on one tramp voyage. The charter party governs relations between owner and charterer, while later cargo buyers rely on the bill of lading. Which document and which law apply in a dispute depends on the wording.
Frequently asked questions
What is maritime transport?
Maritime transport is the carriage of cargo and passengers by ship, and it handles more than 80% of world merchandise trade by volume.
Is shipping cheaper than air freight?
Per ton, usually by a wide margin, though it is slower. High-value urgent cargo tends to fly.
Are maritime transport and the maritime industry the same thing?
The maritime industry is broader and includes shipbuilding, port operation and training. Transport refers to the commercial carriage of cargo and passengers.
What is the difference between tons and deadweight?
Tons measure the cargo carried. Deadweight is the total weight a ship can carry, including cargo, fuel, water and stores.
Sources
- UNCTAD. Review of Maritime Transport press conference, 24 September 2025.
- UNCTAD. Review of Maritime Transport 2025, Chapter 1: Staying the Course in Turbulent Waters.
- UNCTADstat. Maritime and Other Transport, fleet data, 1 January 2026.
- IMO. Fourth IMO GHG Study 2020.
