A trailing suction hopper dredger is a

ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...

that has a full sailing capacity used to maintain navigable waterways, deepening the maritime

canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...

s that are threatened to become silted, to construct new land elsewhere or to replace sand

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is disti ...

by storms or wave action on the beaches. This is made possible by large powerful pumps and engines able to suck sand, clay, silt and gravel.

Operation

Properties

A trailing suction hopper dredger is self-loading/unloading and sometimes equipped with a

pressurized {{Wiktionary Pressurization or pressurisation is the application of pressure in a given situation or environment. Industrial Industrial equipment is often maintained at pressures above or below atmospheric. Atmospheric This is the process by ...

discharging system.

Loading

From the side of the ship one or two suction pipes descend to the bottom of the seabed. On the end of the pipe a so-called trailing drag head is connected. This head is comparable to a large vacuum cleaner and is trailed along the seabed. In the head there are nozzles connected to a high pressure water installation that are capable of loosening the material on the seabed. Due to lower pressure in the pipe, the material will be sucked inward and discharged in the

hopper Hopper or hoppers may refer to: Places *Hopper, Illinois * Hopper, West Virginia * Hopper, a mountain and valley in the Hunza–Nagar District of Pakistan * Hopper (crater), a crater on Mercury People with the name * Hopper (surname) * Grace H ...

. The vessel should always have a positive speed over the ground. It is possible to regulate the density of the sucked substance. If the head is lowered, more material will be sucked but this risks damaging the installation because the material can get stuck inside the pipes. Once the mixture is loaded inside the hopper, the substance will sink and the water is discharged overboard, saving on storage space. A trailing suction hopper dredger can only suck relatively loose substance because the steel teeth are not so big. Harder substances such as rock or ironbased rock must be destroyed by a cutter.

Discharging

There are several ways to discharge a TSHD. The most common way is dumping the material. * Dumping – This is done by simply opening the doors that close the hopper. Once opened the substance will simply drop to the seabed because of gravity. The hopper will never be completely empty because there will always be some residue and water left inside. * Pressing – High-pressure pumps will pump water inside the hopper to loosen or even liquefy the substance, which can then be pumped via long hoses over great distances (f.i. ashore) *

Rainbowing Rainbowing is the process in which a dredging ship propels sand that has been claimed from the ocean floor in a high arc to a particular location. This is used for multiple purposes, ranging from building up a beach to prevent erosion to construct ...

– This is the same principle as pressing, but instead of transporting the substance it will simply be blown away. This is often used to create land. * Crane – It is always possible to discharge the load with a crane, but this will be a time-consuming process.

Equipment

A trailing suction hopper dredger is equipped with the following equipment: * One, or more, rearward extending suction pipes * One or more, Dredging pumps to create an under pressure in order to suck the substance into the hopper * Transportation tubes to transport the substance from the pipes to the hopper * An overflow to discharge the redundant water overboard * Degassing installation to extract any possible gas from the substance in order to reduce damage and increase fluency

Functions

A dredging vessel and particularly a TSHD is mostly used for * Maintaining the depth of a

harbor A harbor (American English), harbour (British English; see spelling differences), or haven is a sheltered body of water where ships, boats, and barges can be docked. The term ''harbor'' is often used interchangeably with ''port'', which is a ...

waterway A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary b ...

. * Constant delivery of sand for land reclamation or

beach nourishment Beach nourishment (also referred to as beach renourishment, beach replenishment, or sand replenishment) describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach ...

References

External links

{{commonscatinline, Suction hopper dredge ships
Ship Knowledge – Ship design, construction and operation

Dredge Engineering
Dredgers