Straddle Carriers - Can they affect cargo completion time?
For vessel operators, fleet managers, and port captains/superintendents, understanding the impact of straddle carrier operations on cargo operations performance is vital. The operation of straddle carriers by a container terminal can directly affect gantry/berth productivity and container ships' cargo operations completion time.
This article explains how container terminals are optimised for straddle carrier operation and the decisions made to ensure the operations are carried out as efficiently as possible. A discussion of potential delays due to straddle carrier operations is also made.
Straddle carriers are a staple of container terminal cargo operations, but did you know that they originated in the lumber industry?
H.B. Ross designed the straddle carrier in 1913 to move lumber around mill yards. The carrier could grasp, lift, and carry lumber significantly longer than the vehicle and proved valuable in both lumber yards and pre-containerisation seaports.
Some seaports eventually adopted the straddle carrier for moving containers, with straddle carriers now a backbone of the global container supply chain.
Why would a container terminal use straddle carriers over chassis or automated guided vehicles?
Straddle carriers are a cost-effective option for container transport within a terminal. Less yard machinery is required as straddle carriers handle container lifts and transportation, unlike chassis and Automated Guided Vehicles (AGVs), which require reach stackers and/or rail-mounted gantries/rubber-tyred gantries (RMGs and RTGs) in the container yard for loading and discharging containers.
This cost-efficiency is offset by increased maintenance and infrastructure costs and specialist operator training required for straddle carrier operations.
How are container terminal layouts optimised for straddle carrier operations?
The following container terminals set out their container in rows, optimised for straddle carrier operations:
DP World Southampton
CTB Hamburg
MPET Antwerp
Europort Fos-sur-Mer
APM Terminals Barcelona
APM Terminals Port Elizabeth, New Jersey
In these terminals, containers are stacked in single-container rows, usually up to a maximum height of three containers high. The container rows are separated by gaps for the straddle carriers to transit the rows. With containers reaching a maximum height of three high, these terminals often have a large terminal footprint.
Linear layout storage in DP World Southampton (Image credit: Intelligent Cargo Systems)
Straddle carriers are also used with block storage layouts, where the containers are stacked by rail-mounted gantries (RMG’s) or rubber-tyred gantries (RTG’s) in large container stacks (usually six or seven containers high), with the straddle carriers providing the transport from the quayside or import gate to the stack.
Examples of these kinds of operations are:
DP World London Gateway
BEST Barcelona
APM Terminals Tangier MedPort
TTI Algeciras
This layout improves the density of stored containers but requires more costly infrastructure in the container yard.
Block layout storage in Hutchison Ports BEST Barcelona (Image credit: Hutchinson Ports BEST)
How can straddle carriers affect quayside performance during cargo operations?
Vehicle speed, operator experience and availability are key factors when analysing berth performance.
Speed
Straddle carriers are defined by the height of containers they can work over. For example, a ‘1-over-2’ carrier can stack a container over two on the ground (three containers high). The largest straddle carrier in a container terminal can be a 1-over-3 carrier, and the smallest can be a ‘1-over-1’.
As straddle carriers' height increases, their maximum horizontal speed must decrease to ensure the vehicle’s stability. It is often a trade-off between the need for a straddle carrier to travel quickly across the container terminal against their ability to service the tallest container stack.
Most container terminals opt for a ‘1-over-2’ for quayside shuttling operations and a ‘1-over-3’ for stacking and yard repositioning tasks.
The shorter straddle carriers have a maximum speed of approx. 30 km/h (18.6 mph), with the taller straddle carriers slower at 25km/h (15.5 mph)
Container terminal operators will always want their fastest straddle carriers shuttling between the vessel and the container stacks.
If a straddle carrier is unable to keep up or is slowed down (carrying heavier containers or moving a further distance to the container drop-off/pick-up point), this will affect the productivity of the quayside operations.
“If a straddle carrier is unable to keep up or is slowed down (carrying heavier containers or moving a further distance to the container drop-off/pick-up point), this will affect the productivity of the quayside operations.”
1-over-3 straddle carrier in MPET Antwerp (Image credit: Intelligent Cargo Systems)
Operator experience
Straddle carriers require high levels of operator training for best performance. The operator normally sits at right angles to the direction of travel and needs good spatial awareness of the vehicle, cargo, and operations area.
The operators must operate at a similar performance level to the gantry or yard operators they move containers between; otherwise, the straddle carrier can be a bottleneck for berth productivity.
Trainees and newly qualified operators should be expected to be more cautious than experienced operators. As such, they might be notably slower than the other straddle carriers working on the quayside.
In addition, weather and environmental conditions on the berth can affect all operators equally. Conditions affecting visibility, such as mist, rain, snow and fog, and vehicle stability, such as high or gusty winds or ice/standing water, will slow straddle carriers.
Straddle carrier availability
When the container terminal plans a vessel's cargo operations, it calculates the optimum number of straddle carriers to assign to each gantry crane.
If the number of straddle carriers servicing a gantry is not optimal, this can directly affect its productivity.
If there are too many straddle carriers per gantry, the gantry will become the bottleneck during cargo operations.
Straddle carriers will be idle, waiting for the gantry to load or discharge containers.
If there are too few straddle carriers per gantry, the straddle carriers become the bottleneck during cargo operations.
Gantry’s will be idle waiting for the straddle carriers to transfer the containers from the yard to/from the quayside.
Availability is flexible during cargo operations. Straddle carriers can be assigned to other vessels within the container terminal. These vessels can have priority due to terminal and shipping company KPI agreements or if a vessel has berth priority for a rapid turnaround.
If a straddle carrier breaks down before or during operations, does that mean departure time will be affected?
The container terminal will plan the cargo operations and include buffer time for delays. If the breakdown duration exceeds the buffer duration, cargo operations completion and vessel departure will be delayed.
Depending on the cargo plan, the terminal can mitigate the delay duration. Suppose multiple gantries are in operation, and a gantry’s productivity is above its target. In that case, it might be possible for straddle carriers from one gantry to be redeployed ad-hoc to the gantry with the most need. Indeed, certain container terminals might not have a fixed number of straddle carriers per gantry, preferring to maintain the flexibility of the straddle carrier’s assigned gantry on a move-by-move basis.
Additionally, depending on the pressure to complete a vessel turnaround, a terminal may opt to assign more straddle carriers from other terminal areas or operational berths.
When a cargo operation is running normally and optimally, any breakdown lasting more than a few minutes will cause a productivity drop. The final section discusses measures to be informed of productivity drops.
Can a straddle carrier terminal layout also affect the duration of cargo operations?
Straddle carriers must transport certain cargoes to/from specific terminal areas. Depending on the container terminal's capacity, most general-purpose cargo will be shuttled to the container stacks nearest to the vessel to keep the shuttling time to a minimum.
Special cargo such as reefer, out-of-gauge (OOG) and some dangerous goods (DG) can be segregated from the general purpose cargo due to specific stowage requirements.
Reefer cargo needs access to shore power connections and easy accessibility for reefer technicians to check and perform maintenance to refrigeration equipment as required.
OOG cargo needs additional yard space as the cargo may be higher, wider or longer than a standard container
Straddle carriers can transport over-height containers, over-width and over-length flat racks when the flat rack cargo fits within the dimensions between a straddle carrier’s legs.
DG cargo may need to be segregated due to provisions of the IMDG code
These handling requirements mean the special cargo areas for reefer, OOG and DG within a container terminal are usually a further distance from the quayside than the general purpose stacks, requiring a longer round-trip time for the straddle carriers.
During the cargo planning stage, the container terminal Terminal Management System (TMS) should consider this extra travel time when calculating the expected completion time for cargo operations.
How can I be informed if a straddle carrier breaks down and/or vessel completion time is in doubt?
Depending on your relationship with the container terminal, they may inform you when the completion time has changed, but they are unlikely to let you know when or why delays have happened. The cause of the delay may only be shared once operations are complete and the terminal departure report has been shared with the shipping company. At this point, the potential for remedial action has been lost.
Proactively monitoring and collaborating with the container terminal as they work your vessels can be the difference between on-time and costly, delayed departures.
Utilising a cargo operations monitoring platform such as CargoMate can provide a real-time view of the operations without needing the terminal to provide regular updates.
There are three details CargoMate measures which can indicate when there are issues with straddle carriers:
Gantry performance for a single gantry is notably slower than the other gantries operating on the vessel
A gantry has an unplanned stoppage or maintenance issue
The crew and/or senior officers onboard have observed and noted an issue with the straddle carriers
Using these three features, CargoMate ensures that port captains can monitor cargo operations with the right information at their fingertips.