There is also a multi-purpose dry cargo ship being developed, which can carry general packaged groceries, as well as bulk cargo and container cargo, etc. This type of cargo ship is more applicable and has higher transportation efficiency than general cargo ships that carry a single type of cargo.

        General cargo ships are widely used, and they rank first in the world merchant fleet in terms of total tonnage. The tonnage of general cargo ships sailing in inland waters is hundreds of tons or thousands of tons, while that of general cargo ships in ocean transport can reach more than 20,000 tons. General cargo ships are required to have good economy and safety, without the need to pursue high speed. General cargo ships usually sail to various ports according to the specific conditions of the source of goods and the needs of freight, with fixed sailing schedules and routes. General cargo ships have a strong longitudinal structure, and the bottom of the hull is mostly a double-layer structure. The bow and stern are equipped with front and rear peak tanks, which can be used to store fresh water or load ballast water to adjust the ship's longitudinal tilt. In the event of a collision, it can prevent seawater from entering the large cabin, which plays a safety role. There are 2 to 3 decks above the hull, and several cargo holds are set up. The hatches are covered with watertight hatch covers to prevent water from entering.

        The engine room can be arranged in the middle or at the rear, each with its own advantages and disadvantages. Arranging it in the middle can adjust the hull's longitudinal tilt, while arranging it at the rear is conducive to the arrangement of cargo space. There are cargo lifting bars on both sides of the hatch. In order to load and unload heavy items, it is usually equipped with a heavy-duty lifting bar. In order to improve the good adaptability of general cargo ships to the transportation of various goods, they can carry large cargo, containers, general cargo, and some bulk cargo. Modern new general cargo ships are often designed as multi-purpose ships. 

        A dry bulk carrier is a ship specially used to load dry bulk cargo. As bulk cargo is not afraid of pressure, in order to facilitate loading and unloading, its cargo holds are all single-deck, with high and large hatch coamings, and a prismatic cross section. The triangular tanks at the four corners of the cargo hold are ballast water tanks, which can be used to adjust the draft and stability height.

        It is generally used to transport bulk goods, so its tonnage is large, and the ports where it first arrives generally have loading and unloading equipment, so large bulk carriers do not need to be equipped with lifting equipment.

        Most dry bulk carriers are single-deck, with no pillars in the hold, but with partitions to prevent cargo from being misplaced in the hold when running in wind and waves. The characteristics are that the hatch coaming is high and large, and the cargo hold has a prismatic cross section, which can reduce the work of trimming the hold. The triangular tanks at the four corners of the cargo hold are ballast water tanks, which can adjust the draft and stability height. Its characteristics are that the cab and engine room are arranged at the rear, and the cargo hold is wide; the inner bottom plate is connected to the side with an upwardly inclined side plate to facilitate the concentration of cargo in the center of the cargo hold, and there are inclined top side tanks at the two sides and the hatch under the deck to limit the movement of cargo; there are more ballast water tanks for ballast navigation.

        Refrigerated ships are special transport ships that keep perishable foods such as fish, meat, fruits, and vegetables in a frozen state or under certain low temperature conditions. Due to the limitation of cargo volume, the tonnage of refrigerated ships is not large, usually hundreds to thousands of tons. The cargo hold of a refrigerated ship is a refrigerated hold, which is often divided into several compartments. Each compartment is an independent closed loading space.

        The bulkheads and doors are airtight and covered with heat-insulating materials such as foam plastics, aluminum plates and polymers to prevent heat conduction between adjacent compartments, so as to meet the different temperature requirements of different cargo types. The height between the upper and lower decks of the refrigerated compartment or between the deck and the bottom of the compartment is smaller than that of other cargo ships to prevent the cargo from being piled up too high and crushing the lower cargo.

        A cargo ship that transports fresh vegetables and perishable goods. It is mostly operated in a regular liner mode, with a speed of up to 20 to 22 kilometers per hour. In order to prevent the transported goods from being crushed, multiple decks are often set up, and they have good heat resistance and moisture retention functions. According to the different forms of refrigeration, refrigerated ships are divided into refrigerated cabin ships and refrigerated container ships. The cargo hold of the former is made into a refrigerated cabin, the bulkhead has good heat insulation function, and the goods are placed in the cabin in the form of pallets or baskets. The goods of the latter are loaded in containers. There are two types of containers, one is a built-in refrigerated container with a built-in freezer; the other is a clutch refrigerated container without a freezer, and low-temperature cold air is injected into the container through the ship's freezer.

        A refrigerated ship is a special ship that carries goods in a refrigerated state. Its cargo hold is a refrigerated hold, and it has several compartments. Each compartment is an independent, closed loading space, and the doors and bulkheads are airtight, and insulation materials are used so that adjacent compartments can carry goods of different temperatures. There are refrigeration devices on refrigerated ships, and the refrigeration temperature is generally -25~15℃. Refrigerated holds often have multiple decks, and the deck height is relatively low to prevent excessive refrigerated products from being crushed. Refrigerated ships have a small tonnage, usually a few hundred tons to a few thousand tons, but a high speed to minimize the transportation time.

        A timber carrier is a bulk cargo ship used to transport timber, also known as a timber transport ship or wood chip transport ship, or simply a timber ship.

        A cargo ship that is used to transport logs and timber. In addition to the structure and equipment suitable for stacking timber, the ship is also equipped with some equipment of ordinary cargo ships to meet the requirements of transporting other goods on the return trip. Most timber transport ships are stern-engined, single-deck, with forecastle, and equipped with topside water tanks or vertical side water tanks.

        1/4 to 1/3 of the wood is piled on the deck, and the height of the cargo pile can sometimes reach more than 5 meters. Therefore, the wood-carrying ship should have a strong deck structure, the equipment on the deck should be as few as possible, and the lifting equipment and its platform should also be located at a higher position. The cargo hold of the wood-carrying ship is very large, and the length of the cargo hold is adapted to the integer multiple of the length of the wood being transported. There are no pillars or other components that hinder loading and unloading in the hold, and there are good ventilation conditions to prevent wood from being contaminated and producing odor.

        The ship is also equipped with complete special fire-fighting equipment to prevent fires caused by wood ignition. In order to fasten the deck cargo timber, upright posts and eye plates for tying ropes are installed on both sides of the deck. The cross-section of the cargo hold of modern timber carriers includes outward-inclined side and vertical side tanks. Outward-inclined side can increase the usable area of ​​the deck, and the increase in ship width is beneficial to stability when fully loaded; vertical side tanks are used as ballast water tanks, which not only improves the utilization rate of the cabin space but also facilitates the loading and unloading of timber. Since the timber on the deck has a certain reserve buoyancy and the ability to resist waves, the freeboard of the ship can be reduced, so the specification has special provisions for the survey and marking of load line marks for timber carriers.

        In order to improve the efficiency of loading and unloading, large-capacity slewing cranes are installed; some also use interconnected ballast tanks to adjust the ship's heel angle and quickly unload bundles of timber on the deck into the water.

       Wood is light in weight and large in size. Therefore, the cargo hold of a wood-carrying ship is wide and there are no beams, columns or other ship components in the cargo hold. As wood is not afraid of wind and rain, it can be loaded in the cargo hold or stacked on the deck. In order to block and protect the wood, wooden pillars are installed on the side of the deck so that more wood can be loaded.

        Container ships, also known as container ships, cargo ship or container ship, are cargo ships that carry standard cargo boxes (called containers) of uniform specifications. Container ships can shorten the time of loading and unloading goods, reduce cargo damage and cargo difference, and improve the economic benefits of operation. Containers are standard cargo boxes made of materials such as metal or fiberglass. Currently, container transportation accounts for a large part of global maritime transportation.

        The characteristics of container ships are that they have containers of uniform specifications stacked in the cargo hold and on the deck, with wide and long hatches, small decks, often double hulls, and are mostly stern-engined ships with short superstructures. Ocean-going container ships usually have bulbous bows and square sterns. Most of them rely on special port cranes for loading and unloading, and a few have their own cranes.

       Container ships can be divided into full container ships and semi-container ships. Their structure and shape are significantly different from conventional cargo ships. Container ships have high loading and unloading speeds, short port stays, and most of them use high speeds, usually 20-23 nautical miles per hour.

        In recent years, in order to save energy, the economic speed is generally adopted, about 18 nautical miles per hour. The speed of container ships sailing short distances along the coast is only about 10 nautical miles per hour. In recent years, about 70%-90% of the groceries imported and exported by the United States, Britain, Japan and other countries are transported by containers.

        Containers can be loaded in the cargo holds and decks of container ships, and the cargo hold covers are strong. Most of them are single-deck structures with wide cargo hold openings. To ensure the strength of the hull and improve the torsion resistance, the hull is designed with a double bottom and double-shell side structure, and a torsion box structure is set on the top of the double-layer side. At the same time, to prevent the movement of cargo containers and to fix the cargo containers, grid-type shelves (cell guide system) are set in the cargo hold. It has high loading and unloading efficiency and less cargo damage and loss. In addition, the main engine power of container ships is large and the speed is high. The box coefficient Cb of ocean-going high-speed container ships is less than 0.6.

        A cargo ship that carries cargo vehicles or loads and unloads containers and other cargo in a rolling manner in a horizontal direction. Its main features are: there is no cargo lifting equipment on board, no cargo hatch on the upper deck, peak cabins at the bow and stern, and the engine room is located at the stern and is almost closed; a gangway is set at the stern, bow, or both sides of the ship to connect to the dock.

        This type of ramp is a distinct feature of ro-ro ships. The stern ramp of a ro-ro ship with a deadweight of 20,000 tons can be as long as 50 meters. The cargo holds are all horizontally divided and have several decks. There is generally no transverse bulkhead in the cargo area. The traffic between the upper and lower cargo holds is connected by a movable (or fixed) ramp or lifting platform between decks. In order to facilitate vehicle driving and stable placement of cargo, all compartment decks do not use ridge arcs and beam arches.

        The cargo hold is equipped with complete ventilation and fire-fighting equipment to promptly discharge the exhaust gas emitted by vehicles during loading and unloading and the volatile gas generated by the remaining gasoline in the fuel tank, which is conducive to safe operation.

        RoRo ships change traditional vertical loading and unloading to horizontal loading and unloading, which greatly improves loading and unloading efficiency and reduces terminal loading and unloading fees. They are particularly suitable for short-distance, non-bridge loading and unloading and transportation of some oversized goods, and are conducive to door-to-door transportation. However, due to the use of multi-layer long cargo hold structure, the ship's anti-sinking ability is poor, the cabin utilization rate and load factor are low, and the construction cost and transportation cost are also relatively high.

        Ro-ro ship, also known as "drive-on-ro-off" ship or "roll-on-roll-off" ship, is a special ship that uses freight vehicles to carry cargo. It is a transport ship that uses a tractor to tow a semi-trailer or wheeled pallet carrying container cargo or other piece cargo to directly enter and exit the cargo hold for loading and unloading.

        A transport ship that carries cargo barges. Also known as a mother-and-daughter ship. It refers to a new type of ship that loads loaded barges into a large ship for transportation. The barge-carrying ship itself is the mother ship, and the barge loaded on the mother ship is the daughter ship. It is a dry cargo ship developed in the early 1970s after containerization. The port congestion in third world countries is very serious. In order to reduce the dependence of ships on port terminals during loading and unloading, it is designed to separate the transportation function from the loading and unloading function.

         Barge carriers are used for river-sea transport. The operation process is to first load the barge (a ship of uniform size, also called a daughter ship) with cargo, then load the barge onto the carrier barge (also called a mother ship), and after transporting it to the destination port, unload the barge into the waters, and then be sent to the destination port by inland river push boats to load and unload cargo and wait for another transport.

        The advantages of barge carriers are that they do not require docks and yards, have high loading and unloading efficiency, short berthing time, and are convenient for river-sea transport. Their disadvantages are that they are expensive, require multiple sets of barges for turnover, require spacious waters with good berthing conditions, and are suitable for river-sea transport routes with relatively stable cargo sources. Therefore, although the first barge carrier was built in the United States as early as 1963, it has not been greatly developed.

 　   According to the way of loading and unloading barges, barge carriers are divided into gantry crane type, lifting type and floating dock type. Gantry crane type barge carriers are equipped with gantry tracks on both sides, and use gantry cranes to load and unload barges at the stern; lifting type barge carriers are equipped with a lifting platform at the stern to load and unload barges, and are equipped with a conveyor to deliver the barges to their place; when loading and unloading barges, the floating dock type barge carrier sinks to a certain depth first, opens the door at the bow or stern, and allows the barge to float in and out. This type of barge carrier does not need to be equipped with lifting equipment, but needs to operate in deep waters, and is limited in terms of use conditions.

       A semi-submersible vessel, also known as a semi-submersible mother ship, submerges its cargo deck into the water by adjusting its own ballast water so that the specific cargo to be transported (such as barges, yachts, ships, drilling platforms, etc.) can be floated from a designated location to the loading deck of the semi-submersible vessel and transported to the designated location.

Semi-submersible vessel

       Semi-submersible vessels are special sea-going vessels that are specialized in transporting large offshore oil drilling platforms, large ships, submarines, gantry cranes, prefabricated bridge components and other extra-long and extra-heavy equipment that cannot be divided and lifted.

        Semi-submersible vessels are called new types of ships in the shipbuilding industry because they combine the characteristics of forklifts, floating vessels, and offshore supply vessels, and have the ability to propel themselves.

        Generally, forklift ships can be loaded and unloaded by rolling and docking with the dock rails, but they cannot be semi-submerged for loading and unloading; floating ships can be loaded and unloaded by rolling and docking with the dock rails, and can also be semi-submerged for loading and unloading, but they usually do not have the ability to propel themselves, let alone cross the ocean; and offshore supply ships have the ability to propel themselves, but they usually do not have the ability to semi-submerge and roll-on loading and unloading. Semi-submersible ships cannot simply be equated with any of the above types of ships.

        Semi-submersibles are also called pontoon barges because a damaged ship can be transported across the sea using a heavy ship called a pontoon barge. This pontoon barge has a long, low deck with tanks that can be filled or pumped out. When the barge sinks below the water's surface, the damaged ship can be towed onto the barge.