I. Main categories and characteristics of dredgers
Dredgers can be divided into the following types according to their working principles and structural differences:
1. Cutter suction dredger
- The underwater soil is broken by a rotating auger, and the mud is sucked in and transported to the mud discharge area with a mud pump.
- Suitable for dredging in inland rivers, lakes and offshore, with high operating accuracy, but weak wind and wave resistance.
- Typical tonnage: small (200-500 tons), medium (500-3000 tons), large (3000-10000 tons).
2. Trailing suction dredger
- The hull is equipped with a rake head mud suction device, which can operate while sailing and has strong maneuverability.
- Mainly used for port and deep-water channel maintenance, suitable for loose mud and sand conditions.
- Large tonnage span: medium (3000-8000 tons), large (10,000-50,000 tons), and super large such as the Dutch "De Beagle" reaching 46,000 tons (data source: International Dredging Association IADC 2022 Annual Report).
3. Chain bucket dredger
- Continuous excavation by chain-driven bucket, suitable for hard soil or rock.
- Tonnage is usually 500-5000 tons. Due to the complex structure, modern applications are gradually decreasing.
4. Other types
- Grab bucket type: tonnage of 100-2000 tons, suitable for local precision excavation;
- Bucket type: tonnage of 200-1500 tons, mostly used for river regulation.
2. Key factors affecting tonnage differences
1. Working environment requirements
- Large offshore projects require high-tonnage ships (such as trailing suction dredgers) to resist wind and waves, while inland projects mostly use small and medium-sized ships.
- Example: Dredging vessels of 10,000 tons or above are commonly used in dredging projects at the Yangtze River Estuary (China Communications Construction Company, Technical Specifications for Dredging Projects).
2. Equipment configuration and function
- Mud tank capacity, power system, etc. directly affect tonnage. The mud tank volume of a large drag-and-suction vessel can reach 20,000 cubic meters, which requires a larger displacement to support it.
3. Balance between economy and efficiency
- Small ships (<500 tons) are low-cost but have limited efficiency, while ultra-large ships (>30,000 tons) are suitable for long-term continuous operations.
III. Professional data reference and trend
According to statistics from the International Maritime Organization (IMO), among the dredgers currently in service worldwide:
- 60% are small and medium-sized (<5,000 tons), mainly used for maintenance dredging;
- 15% are above 10,000 tons, concentrated in large projects such as waterway expansion.
Future trends show that environmentally friendly electric dredgers (such as the Dutch "Boskalis" test ship, with a tonnage of about 8,000 tons) are gradually being promoted.
