Types of Commercial Vessels
There are many different types of commercial maritime vessels and each vessel type is built specifically for the type of cargo that they are transporting. These vessels are built to optimize the transportation process making loading / unloading efficient whilst increasing load capacity and ensuring cargo and crew will be safe during ocean transit.
Dry Cargo Vessel Types
General Cargo Vessels
General cargo vessels are the most basic dry cargo carrying vessel; they are used to carry loose and irregular cargo which is not suitable for container, Ro-Ro, bulk or specialist heavy lift vessels. Stevedores will secure cargoes to these vessels using custom fittings often welded to the ships hold. General cargo vessels are often fitted with rigging for winches which are used to load and unload cargo to the vessel hold(s).
Container ships transport an estimated 52% of all global ocean trade and are specifically designed to transport ISO standardised shipping containers, these include 10, 20, 40 & 45ft standard containers, high-cube containers, open-top containers, flatrack and platform containers (these are used for oversized cargo), tank containers (for liquids / gasses) and refrigerated containers which require a power source to provide temperature control. Container ships are loaded / unloaded using gantry cranes which move the containers straight between the vessel and truck which removes the need for warehousing and improves efficiency. Container vessels come in many different sizes, the world’s largest is the Maersk Triple-E class which is 1306 ft long and has a capacity of 18,340 TEU.
RO-RO or roll-on/roll-off vessels are ships designed to carry wheeled cargo, they come in different forms depending on the need, including vehicle ferries, cargo vessels (which are used for truck trailers, railroad cars etc) and car carriers which are the most prominent. Ro-Ro vessels are loaded/ unloaded using single or multiple loading ramps. The largest Ro-Ro vessel is the Mark V Class owned by Wilh. Wilhelmsen which is 869ft long and has three hoistable decks which provide 138,000 cubic metres of cargo space.
Bulk carriers are used to transport loose dry cargoes such as ore, grains and cement which often have a high weight to cost ratio making ocean transportation by other methods / vessel types inefficient. Bulk carriers are large vessels which are usually divided into separate cargo holds, covered by hatches. Bulk carriers are loaded by spouts, conveyors or by cranes fitted with grabs, some carriers have cranes fitted to allow the loading and unloading of cargo without the need for port equipment. Bulk carriers are usually unloaded using cranes fitted with grabs although some cargoes can be unloaded using specialist equipment to speed up the process. Bulk cargo is generally loaded from the vessel into hoppers which then use conveyor belts to transfer the cargo to open storage or silos.
Crude oil carriers are designed (as the name suggests) to transport crude oil to refineries where it can be processed. Very Large Crude Carriers (VLCCs) and Ultra Large Crude Carriers (ULCCs) are the largest ships in the world. Due to the size of these supertankers many cannot dock at ports so cargoes are unloaded at offshore pumping stations / terminals. Supertankers (VLCCs & ULCCs) can carry approximately 2,000,000 barrels of oil or 318,000 metric tons. The Knock Nevis is regarded as the largest ULCC supertanker ever built with a length of 1504ft although this vessel stopped operations in 2009.
Product carriers are much like crude carriers but generally smaller, they are used to transport refined products from larger terminals to smaller ports located worldwide. These vessels carry products such as petroleum, diesel, asphalt, jet fuel, tar and lubricating oil, the smaller of these product carriers are also used for non-petroleum bulk products such as palm oil.
Liquefied Gas Carriers
Liquefied gas carriers are highly specialised vessels which are used to transport Liquefied Natural Gas (LGN) or Liquefied Petroleum Gas (LPG). The cargo is stored within spherical tanks under high pressure and often at low temperatures. Loading and unloading of these vessels require specialist terminals and handling equipment. LGNs are usually larger than LPGs, the largest type of liquefied gas vessel is the Q-Max which is a 1132ft long LGN vessel and has a capacity of 266,000 m3.
Chemical carriers are used for the transportation of a whole range of chemicals, which each have different properties, characteristics and inherit hazards. Chemical tankers generally have a number of separate cargo tanks which are either coated with specialized coatings such as zinc pait/ phenolic epoxy or they are made from stainless steel. The material used for the cargo tanks or the coating determines what types of cargo each tank can hold, epoxy coated tanks can hold cargoes such as vegetable oil whilst hazardous cargo such as aggressive acids (e.g. phosphoric and sulphuric acid) must be carried using stainless steel tanks.
Specialised Vessel Types
Heavy Lift / Project Cargo Vessels
Heavy lift / project cargo vessels are specialist vessels built to transport extremely heavy or bulky cargoes including heavy industrial components and other vessels, such as yachts. There are two main types of heavy lift / project cargo vessels; semi-submergible (also known as flo-flo or float-on/float-off) which are used for the transportation of other vessels and augment unloading vessels which are fitted with specialist heavy lift equipment to make unloading at under-equipped ports possible. Semi-submergible vessels allow cargoes to be floated into position before the semi-submerged vessel de-ballasts to lift the cargo out of the water.
Livestock vessels are usually converted from other types of cargo vessels and fitted with the necessary equipment to safely transport large numbers of animals. They are designed to provide adequate ventilation, food and water. There is two types of livestock vessels; open livestock carriers with animal pens installed on open decks, providing natural ventilation and avoiding the reliance on mechanical ventilation systems, and closed livestock carriers which have animal pens within holds and internal decks of the vessel. Closed carriers required mechanical ventilation systems but also allow for a more controlled environment which is sheltered during server weather.
Passenger vessels range from small 10 person ferries to large cruise ships capable of carrying more than 6000 passengers. Passenger vessels such as cruise ships are fitted with hotel-like interiors and include facilities such as restaurants, shops, cinemas and swimming pools. The largest passenger vessel is the ‘Allure of the Seas’ which is 1187ft long and can comfortably accommodate 6296 passengers.
A naval ship is a ship (or sometimes boat, depending on classification) used for combat purposes, commonly by a navy. Naval ships are differentiated from civilian ships by construction and purpose. Generally, naval ships are damage resilient and armed with various weapon systems, though armament on troop transports is light or non-existent. The term "warship" is usually used to identify the subclass of naval ships designed primarily as combatants, as opposed to support or yard operations.
Coastal Trading Vessel
Coastal trading vessels, also known as coasters, are shallow-hulled ships used for trade between locations on the same island or continent. Their shallow hulls mean that they can get through reefs where sea-going ships usually cannot (sea-going ships have a very deep hull for supplies and trade etc.).
A ferry is a form of transport, usually a boat or ship, but also other forms, carrying or ferrying passengers and sometimes their vehicles. Ferries are also used to transport freight (in lorries and sometimes unpowered freight containers) and even railroad cars. Most ferries operate on regular, frequent, return services. A foot-passenger ferry with many stops, such as in Venice, is sometimes called a water bus or water taxi. Ferries form a part of the public transport systems of many waterside cities and islands, allowing direct transit between points at a capital cost much lower than bridges or tunnels.
A cable layer is a deep-sea vessel designed and used to lay underwater cables for telecommunications, electricity, and such. A large superstructure, and one or more spools that feed off the transom distinguish it.
Dredging is the repositioning of soil from a marine environment, using specialized equipment, in order to initiate infrastructural and/or ecological improvements. In this definition "repositioning" stands for the process of removal, transport, placement and often treatment of soil; "soil" stands for sediment or silt, as well as for specified soil types like sand, gravel and rock.
A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods. Most barges are not self-propelled and need to be moved by tugboats towing or towboats pushing them. Barges on canals (towed by draft animals on an adjacent towpath) contended with the railway in the early industrial revolution but were outcompeted in the carriage of high value items due to the higher speed, falling costs, and route flexibility of rail transport.
Cargo ships are classified under different categories based on their size, dimension and weight. Most common classifications (at the time of this post) are :
- Handy size, ships weighing between 28,000-40,000 DWT
- Handymax, ships weighing between 40,000-50,000 DWT
- Panamax, the largest size of ship which can pass through the Panama Canal – DWT of between 60,000 to 80,000 tons
- Aframax, generally tankers weighing between 75,000 and 115,000 DWT
- Suezmax, the largest size of ship which can pass through the Suez Canal – DWT of around 150,000 tons
- Malaccamax, the largest size of ship which can navigate through the Malacca Straits – would have a DWT of ideally between 280000 to 300,000 tons in terms of container ships
- Capesize, vessels larger than Panamax and Suezmax, which cannot pass through either the Panama Canal or Suez Canal and has to pass through the Cape of Good Hope and Cape Horn – above 150,000 long tons in DWT
- VLCC (Very Large Crude Carrier), supertankers between 150,000 and 320,000 DWT
- ULCC (Ultra Large Crude Carrier), supertankers between 320,000 and 550,000 DWT
- Seawaymax, the largest size of ship that can fit through the canal locks of the St. Lawrence Seaway – has a DWT of between 10,000 to 60,000 tons