Reach Stacker Components, Stability and Load Charts
The machine
The reach stacker is a counterbalanced machine with a telescopic boom and a spreader (or other attachment) that handles containers. Key elements: chassis and counterweight, outriggers where fitted, boom with lift and crowd cylinders, spreader with twistlocks, tyres and axle loading, and a rated capacity (load moment) indicator with interlocks.
Stability - the core concept
Stability depends on the load moment: load weight × distance from the tipping line. Reach is the enemy of capacity. The load chart gives capacity for a given boom length, boom angle and, crucially, the first and second row handling positions. First-row capacity (container close to the machine) is higher than second-row (boom extended). The chart is machine-specific - never use another machine's numbers.
Traps
- Operating at maximum reach with a light load can still exceed the chart if the boom is long; capacity falls with reach, not just weight.
- Tyre deflection and ground bearing affect stability; a chart assumes firm level ground.
- The load moment indicator is an aid, not a substitute for the chart - and it must be functioning; a faulty indicator means stop.
- Wind acting on a container acts like extra reach - a large sail area reduces effective capacity.
Worked example
A chart shows 30 t at 3 m and 18 t at 6 m. A 20 t container at 6 m is over capacity - the correct action is to reposition closer or use a larger machine, not to "lift slowly".
Rule of thumb
Read the chart for the actual reach and configuration before every lift, and treat the load moment indicator as a backstop you never intend to reach.