Over time, the maritime shipping sector has become a highly specialized industry. Optimizing freight vessels to carry specific types of cargo has allowed companies to improve their efficiency and reduce operational costs. Designed to transport a vast array of goods ranging from automobiles to the gas that fuels them, the merchant fleet of the international maritime shipping industry facilitates approximately 90 percent of all the world’s trade.
Dry Cargo Vessels
Container ships are the most commonly used vessels in maritime shipping, transporting over half of all goods traded by sea. They are also some of the largest merchant ships in the world, with many spanning over 1,300 feet in length and offering capacities of over 18,000 twenty-foot equivalent units (TEU). Maritime shipping companies continue to outperform one another with the development of these megaships—a trend that will likely have a significant impact on the future of the industry.
The advent of container shipping, widely referred to as “containerization,” was a huge boon for global trade as it greatly improved the efficiency of intermodal shipping. The standardized design of shipping containers allows them to be easily transferred from ship to truck or train, removing the often-expensive need for warehouse storage.
The International Organization for Standardization (ISO) has set multiple acceptable sizes for shipping containers, including 10-, 20-, 40-, and 45-foot-long units. However, the common standard is the eight-foot-wide, eight-foot-tall, 20-foot-long unit that gives the TEU its name.
Bulk carriers act as the work horses of the dry cargo sector, transporting loose, pourable goods such as coal, grains, and ore. The high weight to cost ratio of these commodities makes bulk carriers, which are generally around 800 feet long, the most efficient choice for global shipping.
These ships are easily identifiable by their large hydraulic hatches covering several separate cargo holds. Crews load bulk carriers using cranes, conveyors, or spouts, depending on the nature of the cargo, and some vessels are even equipped with onboard cranes for more convenient loading and unloading. After being transported off the vessel, cargo is generally carried in hoppers via conveyor belts to storage facilities or silos. Oftentimes, a ship’s cargo hold must be steam-cleaned while the ship is docked at port in order to safely transport different types of goods.
Sometimes referred to as “breakbulk carriers,” general cargo vessels transport goods that do not require specialized shipping, such as shoes and textiles, which are often transported in pallets or bags. These ships carry cargo in holds similar to those found on bulk carriers, but at an average of 500 feet in length, they typically have fewer compartments than their bulk counterparts. General cargo vessels often feature winch rigging for loading and unloading cargo.
Roll-on/Roll-off, or “RO-RO,” vessels exist in several varieties to carry many types of wheeled vehicles, from consumer automobiles to railroad cars, and are outfitted with ramps to allow for easy loading and unloading. RO-RO vessels encompass cargo ships and smaller ferries, but the most common is the car carrier, which resembles a massive maritime parking garage. Spanning on average more than 600 feet in length, these vessels can carry between 2,000 and 8,000 vehicles.
Refrigerated vessels, or “reefers,” safely carry perishable cargo, such as meat or fruit, in temperature-regulated cargo holds. These vessels have become less common in recent years, as refrigerated units on container ships have become a more economical option.
As their vessel class suggests, crude oil tankers transport crude oil from active oil wells to refineries. Categories of crude oil carriers include Very Large Crude Carriers (VLCC) and Ultra Large Crude Carriers (ULCC), which comprise the largest class of merchant vessels currently at sea. They are so large, in fact, that they often cannot dock at traditional ports and must instead unload their cargo at offshore terminals and pumping stations. These vessels can carry as many as 2 million barrels of oil, the equivalent of 318,000 metric tons.
Product carriers are essentially smaller versions of crude carriers. However, while crude oil tankers transport unrefined oil, product carriers ship refined products such as petroleum, diesel, asphalt, and jet fuel. In some cases, these vessels will also carry non-petroleum liquid products, such as palm oil.
Liquefied gas carriers are specialized vessels designed specifically to transport liquefied natural gas, or LNG. They carry LNG in pressurized spherical tanks, which are kept at the extremely low temperatures necessary to keep gas in its liquid state. The Liquefied Gas category of merchant vessels also includes liquefied petroleum gas carriers, which are slightly smaller than LNGs. Both vessels require special terminals equipped for the loading, unloading, and general handling of these products.
Chemical cargo ships feature specialized designs to carry chemicals safely and effectively. They often include heating and cooling controls to ensure that sensitive materials maintain an appropriate temperature, as well as heavy-duty cleaning systems that allow various types of cargo to be transported without the risk of cross-contamination.