Since the 1960s, the transport of containers has continued to grow. The specific advantage of the use of containers is that the cargo can be transported directly from customer to customer, and not just from port to port. The transport by water is just a link in the chain of transport.
Container vessels have grown from a capacity of 1500 TEU (1966) to approximately 8000 TEU (2002).
Maximum amount of TEUs or FEUs.
Amount of TEUs and FEUs below the weather deck along with their heights.
Number of container tiers.
Presence of cargo gear.
Open or closed ship.
There are two main types of container vessels:
A.Big intercontinental container vessels up to 8,400 TEU (1999)
B.Container Feeder, starting at 200 TEU.
The big container ships can only go to the largest ports because of the ship’s size and the transfer capacity of the port. Large container vessels usually do not have their own loading gear.
Container feeders are small or medium sized ships starting at 200 TEU that specialize in transporting cargo from small ports to large ports, or for use in services which are not profitable for the larger container vessels. The feeder may be equipped with cargo gear. Often multipurpose ships are employed as container feeder.
A common characteristics of all tugboats is their low aft deck. This guarantees that the towing line has some freedom of movement. The point of application of the force in the towing line must be located close to the midships in such a way that the force has no influence on the manoeuvrability.
The towing winch is of great importance because it has to be able to transfer the total force of the propeller to the towing line.
Seagoing tugs are used for:
Salvage, Towing, Anchor Handling in the offshore industry, Environmental Service, Ships with engine trouble.
Partly completed ships, floating wrecks, docks, drilling rigs and other large floating objects that have to relocated can be towed by tug boats. Ever since the introduction of semi-submersible heavy lift carriers, long distance towing is used less often as a method of transport. Coastal states often use seagoing tugs to avert an imminent environmental disaster.
Escort tugs are used to escort (large) ships along dangerous passages. They have been developed after a number of serious (tanker) accidents in recent years. Escort tugs operate in confined coastal waters and are small sturdy seagoing tugs that can push or pull a large ship away from a danger zone when the own propulsion is not sufficient. Escort tugs need to be highly maneuverability and therefore often have azimuth thrusters.
Harbor tugs are used in ports, inland waterways and coastal areas for:
Assisting and towing vessels in and out of ports.
Assisting seagoing tugs when these are towing a bulky object.
Salvaging, or assisting in salvage in ports or coastal areas.
Fighting fires and environmental disasters.
Keeping port free of ice.
Bollard pull: this is the towing force at zero velocity.
Salvage pump capacity
Fire fighting equipment
Means of fighting pollution.
Trailing hopper suction dredger
Trailing hopper suction dredgers are used to maintain or deepen channels and fairways and for construction of artificial islands. These vessels are usually equipped with two adjustable suction pipes, which drag over the bottom to dredge. Dredging pumps in the holds or in the suction pipes pump a mixture of water and material from the sea floor into the holds. Till now (2003) they are able to dredge to a depth of 155m. The holds are called hopper. The solid material precipitates in the hopper. The excess water flows overboard. In order to dredge in adverse weather, the suction pipes are suspended from special cranes, which operate with heave compensation. This ensures that the suction nozzles stay in contact with the seabed.
When the vessel is at its (Plimsoll) mark. It will navigate to the discharging site. The discharging can be done with pressure, using the dredging pumps and the pressure lines at the bow. When the vessel navigates towards the direct vicinity of the dumping location, the discharging can also be done using the spray nozzle, located on the force end. This is called rainbowing. In bot cases, the solid precipitate is mixed with water so that pumps can be used. When the ship reaches the exact dumping location, the cargo is discharged through the bottom flaps. The load is then dumped instantaneously. To facilitate this way of discharging, some small hopper suction dredgers are constructed as two hinged port and starboard halves, which separate when the load is discharged. These vessels are called split rail suction dredgers.
Possible cargo: Sand, gravel, stratum or clayish soil, mud.
Cutter Suction Dredgers
For tougher types of soils, the kind that can not be simply sucked up, cutter suction dredgers are used. These vessels rake the seabed with a rotating cutter and are often used in the development of new ports and new waterways. Cutter suction dredgers can be equipped with their own means of propulsion, but this is not always the case. Spud poles are used to temporarily fix the vessels. The dredgers then move in a swinging motion to deepen the bottom. The loosened soils are washed away through a dredging pump and a floating discharge pipeline to the soil destination. The soil can also be pumped into a barge that can transport the material over larger distances. Cutter suction dredgers are never equipped with a hopper.
Multipurpose means that these vessels can transport many types of cargo. These ships use hatch covers as bulkheads as well as tween decks in the hold. These hatch covers can be placed at varying heights and positions. Usually the head ledges and hatch coamings are of the same dimensions as the holds, which makes loading and discharging easier. The holds are sealed with hatches using a variety of systems. Cargo like wood or containers can be carried on top of the hatches. Often the bulwark is heightened to support the containers.
Possible Cargo: containers, general cargo, dry bulk cargo like grain, wood, cars, heavy items.
Characteristics: dead weight (t), hold capacity (m3, ft3), number of containers and their dimensions, maximum deck load (t/m2), maximum wheel load (T), lifting capacity of cargo gear.
A multipurpose vessel can be subdivided into: ships with cargo gear (up to 120T lifting capacity per crane), ship without cargo gear, coastal trade liners.
A multipurpose vessel can also be equipped with one or more ramps on the side of the ship. Loading and discharging can then commerce through these ramps by forklifts. This is faster and less dependent on the weather.
Trawlers are fishing vessels which drag their nets through the water. In pelagic fishery, the nets are suspended between the water surface and the seabed. In bottom fishery, the net is dragged over the seabed, which requires additional power, especially if the nets are equipped with disturbing chains to churn up the sea floor. The construction and equipment of these fishing vessels strongly depend on the fishing method and the species of fish aimed at. The most important types of trawlers are the cutter and the stern trawler.
Possible cargo: cooled fish (in crushed ice) and frozen fish or shell-fish.
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