Crab Steering Explained: How It Enhances RTG Maneuverability

Rubber Tyred Gantry (RTG) cranes are critical assets in container terminals, intermodal yards, and logistics hubs, offering efficient container stacking and relocation without the need for permanent rails. As operations demand greater flexibility, speed, and spatial efficiency, the maneuverability of RTG cranes becomes a crucial performance parameter. One innovative solution that significantly boosts this capability is crab steering.

Crab steering is a specialized steering mode that allows all the wheels of a rubber tyred gantry crane to move in parallel, enabling the crane to move diagonally or sideways without changing its orientation. This article delves into how crab steering works, its technical foundations, benefits, and why it's an indispensable feature for enhancing the operational efficiency of modern RTG cranes.

Understanding RTG Crane Steering Systems

Before diving into crab steering, it’s essential to understand the basic steering configurations available in RTG cranes. These cranes are mounted on rubber tyres, making them mobile and flexible compared to their rail-mounted counterparts. The standard RTG steering system is designed to allow forward and backward movement along the container yard's layout.

However, due to space constraints and the need for frequent repositioning, RTG cranes are often equipped with advanced steering modes to support complex maneuvers. These typically include:

• Front-Wheel Steering: The front wheels turn while the rear wheels remain fixed.

• Rear-Wheel Steering: Opposite of front-wheel, mainly used during alignment.

• All-Wheel Steering: All wheels turn to create tighter turning radii.

• Crab Steering: All wheels align in the same direction for lateral movement.

Among these, crab steering stands out for its unique ability to move the entire crane sideways without rotating the frame—a game changer for space utilization and operational speed.

What Is Crab Steering?

Crab steering is a mode in which all of an RTG crane’s wheels turn in the same direction and angle. This alignment causes the entire crane structure to move sideways like a crab, hence the name. Unlike traditional turning where the crane must pivot to change direction, crab steering allows movement along a different axis without rotating the frame.

In a typical RTG crane with eight or sixteen wheels (depending on its size and design), the steering system is electronically controlled to synchronize wheel angles. When crab steering is activated, all the wheels rotate to a common angle, and the drive motors propel the wheeled gantry crane laterally.

How Crab Steering Works: A Technical Overview

The crab steering system is governed by a central control unit that sends commands to each wheel module. These modules consist of:

• Hydraulic or Electric Actuators: Responsible for changing the angle of each wheel.

• Encoders and Sensors: Measure wheel positions in real-time.

• Programmable Logic Controller (PLC): Processes inputs and manages wheel alignment.

When an operator selects crab steering mode from the control panel:

1. The PLC calculates the required wheel angle to move the crane in the desired direction.

2. The actuators turn each wheel to that angle.

3. Drive motors engage, moving the crane in a straight diagonal or sideways path.

The system ensures precision synchronization, even under load, allowing the crane to move smoothly across tight yard spaces or align perfectly over container rows.

Advantages of Crab Steering in RTG Cranes

1. Enhanced Maneuverability in Tight Spaces

Crab steering enables RTGs to move laterally, ideal for congested container yards. Operators can adjust the crane’s position without needing a wide turning circle or physically rotating the crane, minimizing disruption to surrounding traffic and equipment.

2. Efficient Container Handling

When a container needs to be picked or placed between tight rows or adjacent stacks, crab steering offers the precision required. This reduces time spent on micro-alignments and improves cycle time per move.

3. Faster Realignment Between Stacking Rows

Traditional movement methods require turning and reversing to shift between rows. With crab steering, RTGs can shift sideways from one row to the next instantly, speeding up yard operations.

4. Reduced Tyre Wear

Conventional turning can cause tire scuffing, especially with heavy loads. Crab steering promotes smooth lateral movement with minimal wheel scrubbing, thereby reducing wear and extending the life of the tyres.

5. Lower Fuel/Energy Consumption

Due to the minimized turning and repositioning, RTGs with crab steering consume less fuel (for diesel-powered cranes) or electricity (for electric models). This contributes to greener, more cost-effective operations.

Use Cases of Crab Steering in Port Terminals

Crab steering is particularly useful in the following scenarios:

• Space-Constrained Terminals: Older or inland container depots with limited maneuvering room.

• Rapid Repositioning: Shifting between stacking lanes or aligning with straddle carriers and terminal tractors.

• Intermodal Yards: Handling containers from rail to truck where precise alignment is critical.

• Obstacle Avoidance: Navigating around yard equipment, temporary obstructions, or ongoing maintenance work.

Many large terminals are retrofitting older RTGs with upgraded wheel modules and control systems to introduce crab steering, underscoring its importance in modern port logistics.

Operator Training and Safety

Operating crab steering requires a certain level of expertise. Most modern RTGs come equipped with operator-assist features, including:

• Auto Alignment Functions

• Joystick-Based Steering Mode Selection

• Real-Time Monitoring on HMI Screens

Safety interlocks ensure the mobile gantry crane cannot switch into crab steering mode under unsafe conditions, such as uneven ground or excessive load shifts. Some systems also provide automated steering correction to compensate for terrain variation or tire slippage.

Conclusion: Why Crab Steering Is the Future of RTG Mobility

As container volumes grow and terminal land remains scarce, the ability to operate RTG cranes with greater agility and control becomes paramount. Crab steering offers a practical, proven solution to the challenges of modern yard logistics. It enables:

• Greater space utilization

• Improved operational throughput

• Reduced crane repositioning time

• Lower maintenance costs

Investing in RTG cranes with crab steering—or upgrading existing fleets—is a strategic move for terminal operators seeking efficiency, safety, and long-term profitability.

In conclusion, crab steering is not merely a technical novelty; it is a functional upgrade that transforms how RTG cranes interact with their environment. With containerized trade evolving rapidly, terminal operators can no longer afford to overlook the enhanced mobility and precision that crab steering delivers.