Dredging vessels are engineering ships used to excavate underwater soil, sand, and gravel. Dredgers include cutter suction dredgers, suction dredgers, bucket dredgers, grab dredgers, and others.
1. Suction Dredger
A suction dredger is a type of dredging vessel that uses a mud pump to suck up the mud and sand from the seabed after it has been turned into a slurry, and then discharges the slurry into a mud tank or designated disposal area. The main types are trailing suction dredgers and cutter suction dredgers.
2. Trailing Suction Dredger
This type of dredger uses a mud rake located in front of the suction nozzle to loosen the soil, and is mainly used for dredging waterways. It has an open-bottom mud tank in the middle, the volume of which indicates the size of the vessel, measured in cubic meters. The mud rake can be single or double. A single rake is placed on either side, in the middle, or at the stern; double rakes are placed on both sides. After the mud rake loosens the soil, a mud pump sucks the slurry into the mud tank. Trailing suction dredgers are self-propelled. After the mud tank is full, the vessel sails to a designated location to discharge the slurry, or uses methods such as high-level side discharge or overflow to dispose of the mud. The rake head, rake teeth, and mud pump liners are all made of high-manganese steel, suitable for dredging silt and sandy clay. The dredging depth is 4-24 meters, and the production capacity is approximately 1000-12000 cubic meters per hour. A transverse thruster is installed in the middle of the bow to facilitate turning, and the propulsion power comes from two main engines. Cutter suction dredgers use a rotating cutter at the suction nozzle to loosen the soil and are mainly used for dredging and filling harbor basins. They are generally not self-propelled. To facilitate relocation at the construction site, some are equipped with propulsion engines. The deck is equipped with 4-6 winches for repositioning, and a lifting cutter frame. The frame has a cutter shaft, and the shaft end is equipped with open or closed cutter blades, inlaid with manganese steel teeth. During dredging, one end of the cutter frame is lowered to the specified depth for dredging. Some have a small bucket wheel rotating at the cutter for dredging, called a bucket wheel dredger. The excavated mud is sucked in by a mud pump along the suction pipe and then discharged to a designated location through a discharge pipe. The dredging pipes include floating water-based dredging pipes and land-based dredging pipes; the former can move with the vessel. The dredging distance can reach 5000 meters. During operation, in addition to using winches to move the vessel, two long positioning piles at the stern can be used interchangeably to ensure a level underwater dredging surface. Cutter suction dredgers are suitable for excavating clay and sandy mud, with a dredging depth of 4-30 meters and a production capacity of approximately 40-4000 cubic meters per hour.
In addition, there are high-pressure water jet suction dredgers and high-pressure mud pump suction dredgers. These utilize high-pressure water pumps to wash away mud and sand through nozzles or use high-pressure mud pumps to suck up mud with a suction head and discharge it to a designated location. The pressure is generally above 10 kgf/cm². They are only suitable for excavating and sucking up mud, sand, and non-cohesive soil. Bucket chain dredgers are dredgers that use a set of bucket chain dredging devices to continuously excavate mud and sand at the bottom of the water. They are used for excavating and filling harbor basins and also for excavating foundation trenches. They are generally non-self-propelled, but some are self-propelled. The bucket chain dredging device mainly consists of a bucket bridge and a bucket chain. The bucket bridge is located in a groove in the middle and rear of the vessel. One end is fixed to a five-sided wheel at the top of the bridge frame, and the free end is equipped with a six-sided wheel. A bucket chain is installed along the bridge surface, consisting of 20-76 buckets connected in a chain. The buckets are directly connected to each other, or connected by chain plates. The bucket capacity is 0.2-0.8 cubic meters. The main engine rotates the upper five-sided wheel through a vertical shaft or an electric motor through a reduction gear, and the lower end rotates the bucket chain through the six-sided wheel for dredging. The excavated mud is dumped into a mud pit when the bucket chain rotates to the top of the bucket bridge, and then discharged into a mud barge via a chute. The mud is then transported to a designated location for disposal or blown ashore by a mud blowing vessel. Bucket chain dredgers are suitable for excavating harder soil layers, resulting in a relatively flat dredged surface. The dredging depth is 3-40 meters, and the production capacity is 20-1000 cubic meters per hour.
3. Bucket Dredger
This type of dredger uses a bucket to excavate hard soil and crushed rock from the seabed. The hull is box-shaped, and the bow is equipped with a rotating bucket excavator that can rotate 130° on a circular track. Dredging is performed by extending and retracting the bucket arm. Bucket dredgers are generally non-self-propelled. There are positioning spuds on both sides of the bow, approximately 25 meters long, and another positioning spud at the stern, approximately 23 meters long. These spuds are used for positioning during dredging, with the stern spud also serving to support the recoil force. Bucket dredgers have a dredging depth of 2–10 meters and a production capacity of 100–240 cubic meters per hour.
4. Grab Dredger
This type of dredger uses a grab bucket to excavate mud and sand from the seabed. The hull is mostly box-shaped, and the deck is equipped with one or two grab cranes that can rotate 360°. Grab buckets come in various types, including flat-mouth, semi-toothed, fully toothed, and petal-shaped. Grab dredgers can be self-propelled or non-self-propelled. Self-propelled vessels have a mud hold; once the hold is full, the vessel sails to the dumping area to discharge the mud. Non-self-propelled dredgers are equipped with barges for mud transport. Grab dredgers have a dredging depth of 3–60 meters and a production capacity of 20–400 cubic meters per hour.
5. Cutter Suction Dredger
Cutter suction dredgers are engineering vessels developed for silt removal, sand pumping, and dredging projects. They are equipped with a cutter head at the front to ensure high silt concentration and long-distance transport, resulting in a high sand content in the dredged water during effective working time.
