Kapal keruk
Artikel Utama: Pengerukan
Kapal Keruk atau dalam bahasa Inggris sering disebut dredger merupakan kapal yang memiliki peralatan khusus untuk melakukan pengerukan.
Ada beberapa jenis kapal keruk diantaranya adalah:
Kapal keruk penghisap / Suction dredgers
Beroperasi dengan menghisap material melalui pipa panjang seperti vacuum cleaner. Jenis ini terdiri dari beberapa tipe.
Trailing suction hopper dredger
Sebuah trailing suction hopper dredger atau TSHD menyeret pipa penghisap ketika bekerja, dan mengisi material yang diisap tersebut ke satu atau beberapa penampung (hopper) di dalam kapal. Ketika penampung suda penuh, TSHD akan berlayar ke lokasi pembuangan dan membuang material tersebut melalui pintu yang ada di bawah kapal atau dapat pula memompa material tersebut ke luar kapal. TSHD terbesar di dunia adalah milik perusahaan Belgia yaitu Jan De Nul TSHD. Vasco Da Gama (33.000 m3 penampung, 37,060 kW total tenaga yang ada) dan perusahaan BelandaBoskalis W.D. Fairway (35.000 m3 penampung).
Pengerukan Indonesia memiliki pula kapal keruk jenis ini seperti TSHD. Halmahera dan TSHD. Irian Jaya. Digunakan untuk melakukan maintenance dredging di pelabuhan-pelabuhan seluruh Indonesia.
Cutter-suction dredger
In a cutter-suction dredger or CSD, the suction tube has a cutter head at the suction inlet, to loosen the earth and transport it to the suction mouth. The cutter can also be used for hard surface materials like gravel or rock. The dredged soil is usually sucked up by a wear resistant centrifugal pump and discharged through a pipe line or to a barge. In recent years dredgers with more powerful cutters have been built in order to excavate harder and harder rock without blasting. The two largest cutter suction dredgers in the world are Dredging International's D'Artagnan (28,200 kW total installed power), and Jan De Nul's J.F.J. DeNul (27,240 kW).
Auger suction dredger
This works like a cutter suction dredger, but the cutting tool is a rotating Archimedean screw set at right angles to the suction pipe.
Jet-lift dredger
This uses the Venturi effect of a concentrated high-speed stream of water to pull the nearby water, together with bed material, into a pipe.
Air-lift dredger
An Airlift (dredging device) is a type of small suction dredge. It is sometimes used like other dredges. At other times, often an airlift is used handheld underwater by a diver. It works by blowing air into the pipe, and dragging water with it.
Bucket dredger
A bucket dredger is a dredger equipped with a bucket dredge, which is a device that picks up sediment by mechanical means, often with many buckets attached to a wheel or chain.
Some bucket dredgers and grab dredgers are powerful enough to rip out coral reef to make a shipping channel.
Grab dredger
A grab dredger picks up seabed material with a clamshell grab, which hangs from an onboard crane, or is carried by a hydraulic arm, or is mounted like on a dragline. This technique is often used in excavation of bay mud.
Backhoe/dipper dredge
A backhoe/dipper dredge has a backhoe like on some excavators. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a pontoon.
The two largest backhoe dredgers in the world are Bean Excavations dredge Tauracavor and Great Lakes Dredge & Dock's dredge New York. Both feature a barge mounted Liebherr 996 excavator: see Bean Excavation and Great Lakes Dredge & Dock.
Water injection dredger
A water injection dredger injects water in a small jet under low pressure (low pressure because the sediment should not explode into the surrounding waters, rather it is carefully moved to another location) into the seabed to bring the sediment in suspension, which then becomes a turbidity current, which flows away downslope, is moved by a second burst of water from the WID or is carried away in natural currents. Opposition claims that Water Injection Dredging is not a natural way of dredging while the side of the WID claims otherwise. As a side note: Water injection results in a lot of sediment in the water witch makes measurement with most hydrografic equipment (for instance: singlebeam echosounder) difficult and should make use of filtering to produce better results.
Pneumatic dredger
Here, there is a chamber with inlets. The water is pumped out of it with the inlets closed. The inlets are then opened to let material in. The chamber is then pumped empty. The cycle is repeated. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.
Bed leveler
This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has the effect of a bulldozer.
Krabbelaar
This is an early type of dredger which was formerly used in shallow water in the Netherlands. It was a flat-bottomed boat with spikes sticking out of its bottom. As tide current pulled the boat, the spikes scraped seabed material loose, and the tide current washed the material away, hopefully to deeper water. Krabbelaar is Dutch for "scratcher".
Fishing dredges
There are types of dredges used for collecting scallops or oysters from the seabed. They tend to have the form of a scoop made of chain mesh. They are towed by a fishing boat. Scallop dredging is very destructive to the seabed, and nowadays is often replaced by scuba diving to collect the scallops.
Amphibious dredger
Some of these are any of the above types of dredger, which can operate normally, or by extending legs so it stands on the seabed with its hull out of the water. Some forms can go on land.
Some of these are land-type backhoe excavators whose wheels are on long hinged legs so it can drive into shallow water and keep its cab out of water. Some of these may not have a floatable hull and, if so, cannot work in deep water. Some makes are:-
- Apollo Duck.
- Sandhurst Group Ltd (click on "Special Products" in the left margin) make a "pontoon dredger". It can float.
- Wright International's Amphibious Dredger.
- Richard Smalley's Amphibious Dredger.
- Inland Dredging Ltd's Watermaster is said to be able to dredge and do various crane-type jobs in shallow water or on land.
- This form by Gendredge Pty Ltd has 4 legs, each with a caterpillar track on its end.
- Susumo Engineering makes a backhoe dredger which has a pontoon hull and can float, and also has wheels on legs.
- Oliver Evans (1755-1819) in 1804 invented an amphibious dredger which was America's first steam-powered road vehicle.
Submersible dredger
These are usually used to recover useful materials from the seabed. Many of them travel on caterpillar tracks.
This link describes a type intended to walk on legs on the seabed. It is a summary of the article "Concept of a mathematical model for prediction of major design parameters of a submersible dredger/miner" by Sritama Sarkar, Neil Bose, Mridul Sarkar, and Dan Walker, in "3rd Indian National Conference on Harbour and Ocean Engineering, National Institute of Oceanography", Dona Paula, Goa 403 004 India, 7 - 9 December 2004: see http://www.nio.org for more information about publisher etc.
Punaise is a subersible dredging pump station. See http://www.damendredging.com/html/en/specials.htm#PUNAISE . (punaise is Dutch for "thumbtack".)
Spider made by Nexans crawls on the seabed on tracks and levels the seabed and lays cable. It is remote controlled from the surface.
I do not know if there are any neutrally-buoyant submarines which can dredge.
Drag
In some police departments a small dredge (sometimes called a drag) is used to find and recover objects and bodies from underwater. The bodies may be murder victims, or people who committed suicide by drowning, or victims of accidents. It is sometimes pulled by men walking on the bank.