Trailing Suction Dredger
A trailing suction dredger is a type of suction dredger. It works by using a drag head located on either side or at the stern of the hull to suck up mud, operating by simultaneously dredging and sailing. Trailing suction dredgers are highly maneuverable, efficient, and resistant to wind and waves, making them suitable for operation in coastal ports, wide rivers, and ship anchorages.
Bucket Chain Dredger
A bucket chain dredger utilizes a series of buckets attached to a chain, driven by an upper guide wheel, to continuously rotate on a bucket ladder. The buckets excavate mud underwater and lift it above the water surface. Simultaneously, the anchor cables are adjusted to move the vessel forward or sideways for dredging. The excavated soil is lifted to the top of the bucket tower, dumped into a mud hopper, and then discharged via a chute into a mud barge moored alongside the dredger. The mud barge is then towed to the unloading area by a tugboat. Bucket chain dredgers are highly adaptable to different soil types, capable of excavating all types of soil except rock. They have a high excavation capacity, produce regular trench cross-sections with minimal error, and are most suitable for projects requiring strict specifications, such as port berths and hydraulic structures. Therefore, they have a considerable range of applications.
Cutter Suction Dredger
A cutter suction dredger is a widely used vessel in dredging projects. It uses a rotating cutter head mounted around the suction pipe at the front of the vessel to cut and agitate the riverbed sediment. The dredged sediment is then transported through the suction pipe to a sediment disposal area using powerful pumps. Its dredging, transportation, and unloading processes can be completed continuously in one operation. It is a highly efficient and cost-effective type of dredger and an excellent underwater excavation machine. The overall length refers to the sum of the hull length and the extended length of the cutter suction frame. The dredging pump is directly driven by the main engine, and the cutter head is driven by an electric motor or hydraulic mechanism. Assuming the dredging efficiency is 30% of the discharge volume, theoretically, a single-stage dredging pump can only suction to a depth of 0M, but in practice, it does not exceed 28M. To increase the suction depth, an intermediate booster pump is needed. The booster pump does not require high head pressure; although its discharge volume is the same as the dredging pump, its power consumption can be greatly reduced. Therefore, the booster pump is generally powered by an underwater high-pressure motor or hydraulic mechanism. With one stage of booster pump, the maximum suction depth is only about 55M. To increase the depth further, the head pressure of the booster pump must be increased, which consequently increases the power consumption. The discharge volume of the dredging pump is generally 1.5 to 2 times the main engine power. For example, if the main engine power is 1200 PS, the dredging pump discharge volume is approximately 1200 * 1.5 = 1800 M³. For cutter suction dredgers, in addition to dimensions, the specifications should include discharge volume (M³/n), head pressure, positioning pile diameter and height, lateral force after traversing, pulling force after positioning pile lifting, dredging depth, cutter head diameter, and rotation speed. The dredging volume is generally between 20% and 30% of the discharge volume. The suction pipe diameter and discharge pipe diameter of the dredging pump should also be provided. This makes the specifications more complete. A workboat is required to accompany the cutter suction dredger, responsible for anchoring and lifting anchors. When buying or selling, attention should be paid to the following spare parts: ① Whether the workboat is included. ② The number of discharge pipes. ③ There should be 4 working anchors, at least two, and anchor buoys. ④ Whether the guide pins for the positioning piles are included.
Cutter suction dredgers are divided into self-propelled and non-self-propelled types: the former, such as the Tianjing, has the highest installed power and dredging capacity in Asia and the third highest in the world; the latter, such as the Tianqi.
Bucket Dredger (Self-propelled)
A bucket dredger is a type of single-bucket dredger that can concentrate all its power on a single bucket for extra-hard digging. It uses a boom and dipper arm to extend the bucket into the water, inserting it into the riverbed or seabed for excavation. Then, a winch pulls the bucket, dipper arm, and boom together, lifting them out of the water to a suitable height. A slewing mechanism rotates the bucket to a discharge point or mud barge, where the bottom of the bucket is opened to release the dredged material, before rotating back to the dredging location. This process is repeated cyclically. Bucket dredgers are suitable for excavating coral reefs, boulders, gravel, large and small stones, clay, coarse sand, and mixtures.
Grab Dredger
Grab dredgers use the boom and steel cables of a rotary excavator to suspend the grab bucket; the bucket is lowered to the seabed by its own weight to grab the sediment. Then, the bucket cable winch is activated, and the bucket cable passes through the pulley at the top of the boom, closing and lifting the grab bucket. The excavator then rotates to a predetermined point (or mud barge) to unload the dredged material. The excavator then rotates back to the dredging location to continue dredging, repeating the cycle. Grab dredgers are mainly used for excavating clay, silt, and boulders, and are suitable for grabbing fine sand and silt. The main power source of a grab dredger is the crane, and the prime mover of the crane is generally a small, high-power, high-speed diesel engine. Its power and the crane's original configuration mainly determine the crane's capacity. Cranes with different boom lengths and lifting capacities exist; a crane with a larger lifting capacity for the same engine power will have a shorter boom length, and vice versa. Generally, cranes on engineering vessels come in three forms: primarily for lifting, primarily for dredging, and a combination of both. Those primarily for lifting generally have longer booms (36-60M), and although their lifting capacity is relatively large, the lifting capacity at a 40°-45° angle (called the direct lifting capacity) is not very large, so their dredging capacity is not necessarily large. Conversely, for those primarily for dredging, a boom length of around 30M is sufficient, and it doesn't need to be very long. In this case, the crane's lifting capacity is relatively large, so the dredging capacity is also large.
Bucket Wheel Dredger
Bucket wheel dredgers are similar to cutter suction dredgers, except for the difference in the excavation equipment. The rotating shaft of the bucket wheel is at a certain angle to the support arm, while the rotating shaft of the cutter head on a cutter suction dredger is parallel to the support arm.
