Reach stackers are heavy mobile machines used to lift, move, and stack shipping containers in ports, rail terminals, logistics yards, and warehouse-adjacent container areas. They matter because container handling speed affects ship turnaround time, rail loading efficiency, truck queues, and the overall cost of freight movement. A reach stacker combines road mobility, high lifting capacity, and a telescopic boom, allowing it to work in tight yards without fixed cranes or rails.
Its design is a practical example of forces, torque, hydraulics, stability, and systems engineering working together.
Key Facts
- Load moment = load weight x horizontal distance from the front axle.
- Weight force is W = mg, where m is mass and g is about 9.8 m/s^2.
- A reach stacker remains stable when the combined center of mass stays inside the support base of the tires.
- Hydraulic pressure creates lifting force by F = PA, where P is pressure and A is piston area.
- Typical loaded container mass can range from 20,000 kg to over 30,000 kg, so safe working load limits are critical.
- Stacking capacity decreases as boom reach increases because torque about the front axle increases.
Vocabulary
- Reach stacker
- A mobile container-handling vehicle with a telescopic boom and spreader used to lift and stack shipping containers.
- Telescopic boom
- An extendable arm made of sliding sections that changes the reach and height of the lifting point.
- Spreader
- The locking frame that connects to the corner castings of a shipping container so it can be lifted safely.
- Load center
- The effective horizontal position where the container load acts on the machine for stability calculations.
- Counterweight
- A heavy mass built into the rear of the machine to balance the torque created by the lifted container.
Common Mistakes to Avoid
- Ignoring boom extension when estimating safe lifting capacity, because the same container creates more overturning torque when held farther from the front axle.
- Treating mass and weight as the same quantity, because mass is measured in kilograms while weight is a force measured in newtons.
- Assuming the machine can lift its rated maximum at any height or reach, because capacity charts change with boom angle, extension, and load position.
- Forgetting ground conditions in stability analysis, because soft pavement, slopes, or uneven yard surfaces can shift the support base and increase tipping risk.
Practice Questions
- 1 A reach stacker lifts a 28,000 kg container. Using g = 9.8 m/s^2, calculate the container weight in newtons.
- 2 A 250,000 N container load acts 4.0 m in front of the front axle. Calculate the load moment about the axle.
- 3 Explain why a reach stacker can lift a heavier container close to the machine than it can when the telescopic boom is fully extended.