Dredger

Designs of a Dredger Ship

A dredger is basically a type of boat. Its name derives from the equipment called dredge, that it has for dredging/scraping the seabed, thereby gathering sediments, which are later on deposited at various locations. Thus, dredgers are often referred to as a dredge also. The basic use of this boat is for dredging which may again be carried out for a number of reasons. Circumstances requiring dredging are discussed below:

Why dredging may be carried out?

There are a number of functions for which dredgers are used. Some of these are listed below.

• Maintaining waterways in a way that they are navigable or deepening waterways where due to sedimentation there is a risk of silting in due course of time, thereby making the passage too shallow for navigation and hampering the access of larger ships.
• Creating new harbors.
• Removing debris from the sea bed
• Mining for sand, rock or clay for usage at some other location for construction of a new land.
• Collecting sediments for minerals like gold, diamonds, etc.
• Mining of sand for placing it on beaches where it has been eroded by storms, waves, etc.
• Removing contaminants form the sea bed. These are chemicals and urban waste that are often a result of spills or storm erosion.
• Commercial fishing for shellfish in shallow waters.
• Preparing for making new bridges, docks, etc.
• For maintenance of the holding capacity of lakes, etc.

While initially dredgers were only used for navigational purposes, with time, their use has become more diverse, thereby making them vital not only for commerce.

Types of Dredgers

Categorically there are three types of dredgers;

• One in which the dredge is dragged along the seabed, collecting shellfish in this process. Certain large dredgers can have up to three dredges on each side.
• Hydraulic dredge bearing dredger wherein the dredge has a powerful water pump to use water jets to pump up the sediments or mollusks from the bottom.
• Mechanical dredgers that are operated with the help of gallows from the bow of the boat

However they can also be classified as ;

• Hopper Dredger: a boat that collects sediments and hauls it into a hopper(a large onboard hold)
• Suction Dredger: usually a stationary vessel, this is the most common type of dredger. It makes use of suction pump for mining sand.
• Bucket Dredger: make use of equipment that picks up sediments by mechanical means. These have circulation buckets attached to a wheel.
• Trailer Suction Hopper Dredger: here the dredge has a series of suction pipes that haul material with the help of certain pumps and deposit it into the hopper. When the hopper is full the material is dumped at the disposal area.
• Cutter Suction Dredger: are used for construction and related activities. These have a cutter like head at the suction mouth and are used for hard surfaces like coral reefs, rocks, etc.
• Bed Leveler Dredger: are used for leveling the sea bed.
• Water Injection Dredger: these dredgers use a jet to inject water at relatively low pressure in order to make the sediment suspend, and later carrying this loosened material with the help of a burst of water.
• Jet Lift Dredgers : use a burst of water to lift the sediments off the sea bed into the pipe.Thus the classification of dredgers can be done in accordance to the function performed by them or by the type of dredging equipment they use.

 

Dredge boats therefore primarily play a role in keeping the water transport unimpaired by facilitating easier access and traversing through sea channels, in addition to other functions mentioned above. This not only is vital for the commerce but also from the environmental point of view. However, care must be taken as too much of dredging is harmful for the ecosystem.

Image credit

www.scalemodelsweston.co.uk

www.landingcrafts.net