Port Crane Selection Guide: RTG vs RMG vs Ship-to-Shore — Engineering & Operations Comparison

The Port Crane Ecosystem

Container terminal productivity is measured in moves per hour — and the cranes that load and unload vessels, stack containers in the yard, and transfer boxes to trucks are the machines that drive this number. Getting the crane mix wrong in a terminal design costs operators millions in lost productivity and creates bottlenecks that persist for decades.

The three primary crane categories in a modern container terminal are:

• Ship-to-Shore (STS) / Quay Cranes — load and unload vessels at the berth
• Rubber-Tyred Gantry (RTG) — stack containers in the yard, move on rubber tyres
• Rail-Mounted Gantry (RMG) — stack containers in the yard, move on rails

Each has a distinct role, distinct economics, and distinct automation potential. This guide gives terminal operators, port developers, and equipment procurement teams the technical framework to make the right selection.

Port Crane Type Comparison Matrix

Parameter

STS Quay Crane

RTG

RMG

SWL (typical)

40–65 t under spreader

40–50 t

40–50 t

Outreach (max)

Up to 72 m (25 rows)

N/A (yard stacking)

N/A (yard stacking)

Stacking height

N/A

4–6 high (1 over 5)

6–9 high (1 over 8)

Power source

Shore power (electric)

Diesel/electric hybrid

Electric (grid/catenary)

Automation potential

Semi/fully auto

Semi-auto (ARMG)

Full automation (ARMG)

Flexibility

Fixed berth

High — row reassign

Low — fixed rails

Capex (relative)

$$$$ per unit

$$ per unit

$$–$$$ + rail infra

Ship-to-Shore (STS) Quay Cranes

STS cranes (also called ship-unloaders in general terminology, but "STS" or "quay crane" specifically in container terminals) are the gateway to every container terminal — the cranes that physically transfer containers between the vessel and the quay.

Technical parameters:

Modern STS cranes are sized to the vessel classes they must serve. With the dominance of Ultra-Large Container Vessels (ULCVs) exceeding 24,000 TEU, STS cranes must reach across 25 container rows — requiring outreach of 67–72 m from the quay wall. Key specifications:

• SWL: 40–65 t under spreader (with twin-lift spreader capability on premium units, allowing two 20' containers simultaneously)
• Outreach: 52 m (Panamax), 60–65 m (Post-Panamax), 67–72 m (Super Post-Panamax)
• Back reach: 15–20 m (behind the quay wall for container handoff to the yard)
• Lift height above rail: 38–50 m
• Hoist speed: 90–120 m/min (loaded); 180–200 m/min (empty)
• Trolley speed: 180–240 m/min
• Slew: STS cranes do not slew — they are traversing gantries running on quay rails, with a trolley traversing the fixed boom
• Rail gauge: 15.24 m (50 ft) standard; some terminals use 30 m gauge for high-capacity cranes

STS crane procurement lead times: 18–28 months from order to delivery for major OEMs (ZPMC, Liebherr, Konecranes, Gottwald/Terex). ZPMC (Shanghai Zhenhua Heavy Industries) supplies approximately 70% of the global STS market.

Key design choices for STS crane procurement:

• Hinged vs fixed boom: Hinged booms raise clear of the vessel's superstructure when not in use; required for some berth configurations but heavier and more expensive
• Single trolley vs dual trolley: Premium dual-trolley STS cranes use an intermediate platform and transfer trolley to eliminate ship-to-shore transport cycle bottleneck — increases moves per hour by up to 25% on high-productivity berths
• Spreader type: Standard single 20'/40' spreader vs twin-lift vs tandem lifts — choice depends on container mix and productivity targets

Rubber-Tyred Gantry (RTG) Cranes

RTGs are the most common yard crane in global container terminals, operating on rubber tyres and able to relocate between container rows without rail infrastructure. The standard RTG configuration straddles 6–7 lanes of containers and stacks 4–6 high (typically designated "1-over-5" — stacking 5 boxes and lifting to position a 6th on top).

How RTGs work: The RTG operator sits in a cab at the top of the gantry and drives the crane to a specific row. The spreader lowers to pick the target container. The RTG then travels down the row to the truck lane, where the container is placed on a truck or trailer. RTG cycles are typically 3–4 minutes per move under manual operation.

Power systems — the critical choice:

Diesel-powered RTGs (DRTGs): Traditional configuration. Simple deployment — no infrastructure. High fuel cost and emissions. Being phased out of new terminals in Europe and increasingly Asia due to emission regulations.

Diesel-electric RTGs: Diesel engine drives a generator; all motions electric. Better energy recovery through regenerative braking. Mid-range fuel consumption.

Electric RTGs (ERTGs) / Plug-in hybrid RTGs: Connect to a trailing cable reel or on-board battery at the end of each row. Near-zero emissions during operation. Higher infrastructure cost (power distribution). The dominant specification for new terminal developments from 2022 onwards.

Automation — ARMG: Automated Rubber-Tyred Gantries (ARTGs) replace the cab operator with a remote operator who manages exception handling only. A single remote operator can supervise 4–8 cranes simultaneously. ARTGs require camera systems, laser profiling, and a sophisticated TOS (Terminal Operating System) integration. Investment payback: typically 4–7 years on a high-throughput terminal.

Leading RTG manufacturers: Konecranes, Liebherr (Noell), Kalmar (Cargotec), ZPMC, Weihua, SANY.

RTG sizing example — standard specification:

Rail-Mounted Gantry (RMG) Cranes

RMGs operate on fixed rails embedded in the terminal yard. Unlike RTGs, they cannot relocate between rows — each RMG is dedicated to one block. However, this constraint enables significantly higher automation reliability, higher stacking density, and lower energy consumption.

Why RMGs enable higher automation: The fixed rail path eliminates the most complex challenge in ARTG automation — accurate positioning on an unpaved, potentially uneven surface. RMGs know exactly where they are at all times. This makes full unmanned automation more reliable and more economical to implement.

Higher stacking density: RMG blocks can stack 6–9 containers high (typically "1 over 7" or "1 over 8"), significantly improving ground slot utilisation compared to RTG blocks. In terminals where land is expensive (Singapore, Rotterdam, Hamburg), this is economically decisive.

The infrastructure trade-off: Rail installation is expensive — a double-rail block for an RMG costs significantly more per metre than a paved RTG surface. RMG blocks are also inflexible — adding capacity requires new rail infrastructure. For terminals expecting significant configuration changes or uncertain throughput growth, RTG flexibility has real option value.

Automated RMG (ARMG) terminals: APM Terminals (Rotterdam, Los Angeles, Medcenter), DP World (London Gateway), PSA Singapore, and Yildirimlar (Mersin) are benchmark ARMG operations. Container flow in these terminals moves from STS to Automated Guided Vehicles (AGVs) or Automated Straddle Carriers (ASTRACs) to ARMGs without human intervention in the main flow.

Hybrid Terminal Configurations

Most terminals do not use a single crane type exclusively. Common configurations:

STS + RTG (most common globally): Universal configuration for medium and large terminals. Simple to operate, flexible, no rail infrastructure. Used in most Indian ports (JNPT, Mundra, Adani, DP World), all GCC container terminals, and the majority of Southeast Asian ports.

STS + RMG (automated or semi-automated): Preferred for greenfield developments in high-labour-cost economies or where land premium requires high stacking density. Rotterdam Maasvlakte 2, London Gateway.

STS + Straddle Carriers: High-productivity but complex. Used in some European and Australian terminals. Straddle carriers can stack 2–3 high and carry containers — they do both transport and stacking. Very high capex.

Selection Framework

Use these questions to guide crane selection in a terminal design:

1. What vessel classes will call at this terminal? → Determines STS outreach. If ULCV calls are planned, specify 67+ m outreach.

2. What is the target throughput in TEU/year? → Determines the number of STS cranes and yard crane density required. Rule of thumb: 1 STS crane handles 150,000–250,000 TEU/year; 1 RTG block handles 20,000–30,000 TEU/year.

3. What is the land area available? → Constrained land favours RMG (higher stacking density). Abundant land with uncertain growth favours RTG (flexibility).

4. What is the labour cost environment? → High labour costs make automation investment viable faster. Low labour cost markets see longer payback on automation — but automation also provides predictable productivity regardless of labour availability.

5. What is the power infrastructure status? → ERTG/RMG require reliable, high-capacity grid connection. If port power infrastructure is weak or unreliable (common in West Africa), diesel-electric RTGs with on-site generation may be the practical choice.

Key Takeaways