A dragline excavator is a large earth-moving machine whose bucket hangs from a long boom and is operated with two ropes — the hoist rope and the drag rope. The bucket is swung outward, dropped onto the ground, dragged back toward the machine (‘drag-line’), then hoisted and dumped.
How a dragline works
The dragline operating cycle is surprisingly simple but very effective:
- The bucket is swung forward on the boom
- The hoist rope pays out and the bucket drops onto the ground
- The drag rope pulls the bucket toward the machine, scooping up soil
- The hoist rope lifts the loaded bucket
- The machine swings and the bucket is emptied
Dragline buckets on the largest mining machines can hold hundreds of cubic metres.
Types of draglines
- Crawler dragline — moves on tracks, common in European earthworks
- Walking dragline — gigantic mining machines that walk on shoes
- Pontoon dragline — on a floating pontoon for dredging and bank work
- Mobile dragline — smaller wheel-mounted versions for flexible use
Applications
Draglines are mainly used for:
- Dredging — deepening waterways, ditches and harbours
- Mining — stripping overburden above coal and ore seams
- Canal construction — excavating channels and stormwater basins
- Dyke work — winning clay for dyke reinforcement
- Sludge removal — scooping silt from waterway beds
Pros and cons
Advantages:
- Reach of 50 m or more from one position
- Works underwater without dewatering
- Low ground pressure thanks to tracks or pontoon
- Long service life and high reliability
Disadvantages:
- Less accurate than a hydraulic excavator
- Slow cycle time
- Requires highly skilled operators
- Inconvenient on small sites
Related terms
- Excavator
- Dragline mat
- Backhoe
- Dewatering
- Bank protection
- Earthworks
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