Ships are mostly classified along the line of the functions they perform. Apart from military vessels, most commercial vessel classes can be along the following categories: cargo carriers, passenger carriers, industrial ships, service vessels, and noncommercial miscellaneous.
These are vessels that are designed for the sole purpose of cargo transportation. For macro-identification, cargo ships can be distinguished by the type of cargo they carry. Fortunately, the superstructure design and construction of vessels for specific cargo type tends to be distinct. This means that it is easy to distinguish container, bulk and passenger carriers from each other by their unique appearances.
Container carriers are primarily used to transport inter-modal containers at sea. The popularity of these types of ship had increased over the years due to the increased impact of shipping containers as the primary driver of globalization. The vessels are built with cellular grid of compartments below deck and above the deck. It is these grid networks that holds either standard 20, 40 or 45 footer shipping containers.
Container carriers are about the most popular type of vessels as the volume of container shipments increased considerably worldwide. About 90% of unitized cargo in world are shipped by container. The cargo carrying capacity of these types of vessels are measured in TEU (Twenty-Foot Equivalent- that is the number of 20 foot containers that the vessel can accommodate).
RORO (Roll-on/roll-off) Vessels
Roll-on/roll-off vessels are ships that are designed to transport wheeled cargoes. These include cars, buses, trucks and construction/heavy equipment. These types of vessels are easily distinguished by large doors in the hull and external ramps that can open outwards and downwards to allow rolling of the wheeled cargoes between the port pier and the ship.
The interior of the vessel tend to resemble huge parking lot which are constructed at multiple layers within the deck in order to fully maximize its internal cargo carrying capacity.
A RORO Carrier.
General Cargo Vessels
Before the advent of Container carriers, these were the most popular cargo carrying vessels in the world. They are designed to carry all forms of unitized cargoes and these are designated by the type of packaging. These could include bags, palettes, crates, boxes, cartons and even shipping containers. Some of these type of vessels are fitted with deck cranes to facilitate unassisted cargo evacuation.
Tankers are vessels designed to transport bulk liquid cargoes.Most of these cargoes include crude and refined petroleum products, liquefied natural gas, liquid chemical materials, vegetable oil etc. These types of vessels are constructed with multiple cargo holding tanks within the ship hull. The liquid cargo is loaded and unloaded through the use of series of pumps and pipes.
Dry bulk vessels are designed for the carriage of ore, coal, grain, fertilizer etc. Appearance wise, they tend to resemble container vessels without the trademark container cargoes. One of their main features are multiple large cargo hatches that covers the cargo compartments within the ship hold. Some bulk carriers have on-board cranes with bucket heads to offload their cargo volume while others without these might need ship side equipment for the same task. The cargo is mostly evacuated through the use of suction pumps, chain buckets etc.
Most passenger ships fall into two sub-classes, cruise ships and ferries.
Cruise ships are derived from the transatlantic ocean liners, which, since the mid-20th century, have found their services supplanted by jet aircraft. These ships are designed for large numbers of passengers on vacation. They are characterized by high superstructures of many decks with hotel-like, outlined rooms for passengers. In addition to this major social facilities that may be found onshore are replicated in the ships. These include casinos, shopping malls, dance clubs and theaters. Many cruise ships have stern ramps, much like those found on cargo-carrying roll-on/roll-off ships to facilitate passengers transfer.
Most of these cruisers are painted white because their routes lie in warm seas.
Ferries are small to medium sized vessels that designed to carry passengers and (sometimes) vehicles on hinterland waterways. The vessels are mostly made up of one or multiple decks. Ferries are not designed to be used in the rough, open waters of the seas like the big ocean going vessels but are designed for calmer waterways, mostly in urban areas, where large volumes of passengers need to be commuted daily.
Industrial ships are vessels that are purpose built to carry out an industrial processes at sea. A good example is a factory ship that processes fish at sea. The final products include fillets, canned fish and fish meal. In the petroleum sector, industrial ships include floating oil drilling or production rigs and Floating Production Storage and Offloading (FPSO) vessels. These types of vessels are characterized by the specialized equipment they carry onboard for the extraction and processing of items of value at sea into a final product.
A circular FPSO being transported to sea.
Tug boats are high powered vessels that are used in tugging or towing vessels. This activity is mostly carried out in port approaches, navigational channels, harbors and inland waterways where the use of the ships propulsion might be damaging to surrounding facilities or the environment. Although Tug boats are relatively smaller when compared to ocean going vessels, they are primarily designed to provide towing capacities for the bigger vessels. Due to this factor, they carry more power to size ratio than any other vessel type.
Platform Supply Vessels (PSVs)
Platform Supply Vessels (PSVs) are specialized vessels that are designed to supply offshore oil and gas facilities. The primary usage of these vessels is supply of logistic support and transportation of goods, materials, equipment and personnel to and from these platforms. This broad class of vessels can be subdivided into offshore vessels (OSVs), crane vessels (CVs), offshore construction vessels (OCVs), well stimulation vessels(WSVs) etc.
An Offshore Supply Vessel.
Other Types of Vessels
A barge is a type of flat-bottomed vessel that is designed for transportation of goods on rivers and canals. They are broken into two major categories: those that are self propelled and those that need external power, either by tugs or pusher boats.
A Barge carrying bulk coal.