Instruments and Monitoring System of Trailing Suction Hopper Dredger

Trailing Suction Hopper Dredger: Instruments and Monitoring System

Main Dredging Instruments of Trailing Suction Hopper Dredger:

Pressure gauge (vacuum gauge), flow meter, densimeter, loading indicator, drag head depth position indicator, dredging monitoring systems.

1) Pressure Gauge (Including Vacuum Gauge)

Elastic pressure instruments are widely used in dredging. According to different sensor types, pressure gauges are usually classified into Bourdon tube pressure gauges, bellows pressure gauges, diaphragm pressure gauges, etc.

2) Flow Meter

The flow meter is mainly used to monitor the axial flow velocity of slurry medium in the discharge pipeline in real time. Its core technical purpose is to ensure that the flow velocity is always maintained above the critical deposition flow velocity, using fluid suspension force to overcome the settlement effect of solid particles and prevent sediment accumulation or pipeline blockage caused by insufficient flow velocity.

Meanwhile, by accurately monitoring flow velocity data, operators can combine feedback from the densimeter to find the optimal operating point within the safe boundary of hydraulic transportation, optimize the speed and output power of the dredge pump, maximize slurry concentration and transportation efficiency on the premise of ensuring full-flow pipeline transportation, and avoid unnecessary frictional loss and energy waste caused by excessive flow velocity.

3) Densimeter

Densimeter (also known as concentration meter) is used to measure the density or concentration of slurry in real time.

Measure dredging efficiency: Density is the most direct indicator to measure the working efficiency of a dredger. It reflects the amount of solid soil contained in a unit volume of slurry. The higher the density, the more soil is dredged and the higher the transportation efficiency. Low density may indicate poor digging performance of the drag head or excessive intake of clear water.

Control the loading process: Densimeter data is critical when the trailing suction hopper dredger loads slurry into its own hopper. Operators judge the hopper loading status by monitoring density changes. When the hopper is nearly full, the density will change, and a decision can be made to continue loading, start overflow (discharge upper clear water to load more soil) or stop operation.

4) Loading Indicator

Trailing suction hopper dredgers are usually equipped with a loading indicator that automatically records the loading volume of dredged earth. This device measures the ship’s draft using multiple pressure sensors installed at the bottom of the ship, converts pressure signals into current signals through a converter, and the computer processes the signals to calculate and record the dredger’s displacement and mud loading capacity, displaying the loading process in real time.

5) Drag Head Depth Position Indicator

The drag head depth position indicator processes data signals from the drag arm angle sensor, ship draft sensor, tide level telemeter, GNSS positioning system, etc., through the computer system to display the drag head position, dredging section and plane position in real time. It also has functions such as automatic record storage and printing.

6) Dredging Monitoring System of Trailing Suction Hopper Dredger
According to the functional complexity and technical level, the dredging monitoring system of trailing suction hopper dredger is divided into basic dredging monitoring system and extended dredging monitoring system.

(1) Composition of Basic Dredging Monitoring System

The basic dredging monitoring system consists of the following subsystems:

① Dredging trajectory and profile display system.

② Draft and loading monitoring system.

③ Equipment control and monitoring system.

④ Monitoring and alarm system.

⑤ Dredging instruments.

(2) Composition of Extended Dredging Monitoring System

In addition to all subsystems of the basic dredging monitoring system, the extended dredging monitoring system also includes the following subsystems:

① Automatic dredging control system.

② Dredging auxiliary decision-making system.

③ Power management system.

④ Dynamic positioning / dynamic tracking system.

Dredging Operation Technology of Trailing Suction Hopper Dredger

The trailing suction hopper dredger is a self-propelled longitudinal dredger that dredges while sailing. It does not need anchoring and layout during operation, nor does it require auxiliary ships.

Generally, only sensitive navigation marks need to be set on the shore, including boundary marks, midline marks, start marks, end marks, etc. In recent years, with the popularization and application of DGNSS, the navigation and positioning of dredging operations have been greatly facilitated, which not only improves positioning accuracy and tracks the operation trajectory of the ship in real time. At present, no water-land dredging marks are preset for dredging, and DGNSS is directly used to control the ship position for dredging.

FAQs: Trailing Suction Hopper Dredger

Q1: How is a trailing suction hopper dredger classified?

A1: It is classified by hopper capacity into four levels: Small: q < 4000 m³; Medium: 4000 m³ ≤ q < 9000 m³; Large: 9000 m³ ≤ q < 17000 m³; Ultra‑large: q ≥ 17000 m³.

Q2: What are the objective factors affecting the time utilization of dredgers?

A2: Strong wind, high waves, dense fog, current, ice, tide, and construction interference.

Q3: What are the main dredging instruments of a trailing suction hopper dredger?

A3: Pressure gauge (vacuum gauge), flow meter, densimeter, loading indicator, drag head depth position indicator.

Q4: What constitutes the basic dredging monitoring system?

A4: ① Dredging trajectory and profile display system; ② Draft and loading monitoring system; ③ Equipment control and monitoring system; ④ Monitoring and alarm system; ⑤ Dredging instruments.

Q5: What constitutes the extended dredging monitoring system?

A5: It includes all basic subsystems plus: ① Automatic dredging control system; ② Dredging auxiliary decision‑making system; ③ Power management system; ④ Dynamic positioning / dynamic tracking system.

Q6: What does the deployment of a trailing suction hopper dredger include?

A6: No anchoring or auxiliary vessels required. The dredger approaches the starting point, confirms position, lowers the drag head, starts the dredge pump, and enters the dredging trench.

Q7: What are the construction methods of a trailing suction hopper dredger?

A7: Hopper loading (overflow), bypass/side casting, and rainfilling construction.

Q8: What environmental protection measures should be taken during overflow loading?

A8: Monitor back silting, control turbidity, avoid impact on aquaculture and water intakes; no overflow when dredging contaminated soil.

Q9: When is bypass/side‑casting used?

A9:
① Sufficient current to carry sediment away from the dredging trench;
② Shallow water insufficient for loaded draft;
③ Emergency rapid dredging;
④ Permitted by environmental authority with no obvious back silting risk.

Q10: How to operate the bottom doors during bow rainfilling?

A10: Open water valves first; open/close doors symmetrically in sequence; adjust water valves to match flow and concentration; flush the pipeline completely before stopping.

Q11: How to position and anchor when starting dredging?

A11: For spud positioning: lower spud after stopping. For anchor method: set stern anchor first; re‑position after anchoring.

Q12: How to dredge in a short dredging trench?

A12: Use reciprocating dredging; use forward‑and‑backward dredging if no turning space.

Q13: How to select the drag head?

A13: Fluid silt / loose sand: scouring type; Medium dense sand: scouring type + high‑pressure water; Silt / soft clay: digging type; Dense sand: digging type + high‑pressure water or active digging type; Stiff clay / loose gravel: active digging type + high‑pressure water.