Terminal Productivity Container Management

T E R M I N A L P R O D U C T I V I T Y

38 • CONTAINER MANAGEMENT • August 2007

Increased volumes,vessel sizes andservice standardsrequire higher berthproductivity from

terminal operators. It hasbecome obvious that ever-increasing crane intensity forvessel operations is notalways the right answer tothe challenge. If we considerthat berth productivitydemand nowadays and forthe coming years is atminimum 200 containers perhour (cont/hr), and that thepractical number of cranesallocated for the vesselshould not exceed six, thanthe sustainable gross rate (alldelays included) should be atleast 35 cont/hr.

The technicalproductivity rate forconventional cranes isgreater than 45 cont/hr, butnot many terminals in theworld have a sustainableproductivity rate at this level,even if they allocate anadequate number of primemovers to the cranes. Asresult, terminal operators and

crane manufacturers areseeking new ways to boosttheir cranes’ productivity.Historically, increasing thenumber of 20 ft containerson-deck and in 40 ft cellsunder-deck has driven themove to increaseproductivity by handling two

20 ft containers ‘end to end’simultaneously (twin-lift). Asa result, most conventionalcranes are now equippedwith telescopic spreaderswhich can handle twin-liftsas well as single lifts.

When the spreader isextended, the crane can lift a

single 40 ft, 45 ft of 48 ftcontainer or twin containers.When the spreader isretracted, it can lift single 20ft containers. Most spreadersare adjustable: they adjust tothe gap between two 20 ftcontainers and can be used toperform twin-lifts in anydeck/cell arrangement. Mostof the cranes used in twin-liftoperations have a liftingcapacity of 65 tonnes, whichallows them to handle ‘heavylifts’.

Currently, the centre ofattention for many terminaloperators has moved tocranes with dual and triplespreaders. Several ports havecommissioned dual spreadercranes manufactured byShanghai Zhenhua PortMachinery Co, Ltd (ZPMC).About 60 such cranes havebeen commissioned and anadditional 85 are currentlyon order, according toZPMC.

The most commonlyadopted configuration fordual spreader cranes consistsof two independent sets of

In pursuit ofproductivity

In part one of a two-part article, Alexandre Goussiatiner investigates productivity

rates for multi-spreader quayside cranes compared with single-lift alternatives

Alexandre Goussiatiner


August 2007 • CONTAINER MANAGEMENT • 39

hoists, head blocks andtelescopic spreaders similarto the ones fromconventional cranes (seeFigure 1).

Mechanical linkagesbetween the two sets are usedto adjust to differentcontainer heights and toadjust side-to-side clearancesof two containers quaysidewhile landing them onto

adjacent terminal trucks.When sets are connected toeach other, the crane canperform various dualspreader (tandem) lifts: two20 ft containers side-by-sidewith retracted spreaders, twotwins side-by-side withextended spreaders, etc. Allpossible lift types are listedin Figure 2.

When the sets are not

connected, the crane isoperationally identical to aconventional single spreadercrane.Disconnection/connectiontakes less than a minute, butcan be performed only whilethe spreaders are grounded onthe quay surface. The ratedcapacity of the cranes is 80tonnes under two spreaders or65 tonnes under one spreader

(see Figure 4). A smallnumber of dual-hoist craneshave been built with 120-tonne lifting capacity undertwo spreaders.

Just recently ZPMC hasmade further advances with atriple-spreader crane. The firstthree triple-spreader craneswere commissioned at MawanTerminal in the Port ofShenzhen in China inFebruary 2007. The craneconfiguration consists of threespreaders, two head blocksand two hoists. Twoinseparable spreaders on thewaterside are connected to athird spreader on the landside(see Figure 3).

The crane operates usingthe following modes: Three spreaders mode:

landside spreader isconnected.

Two spreaders mode:landside spreader isdisconnected and hoisted up.

One spreader mode:waterside spreaders aredisconnected and hoistedup. Only the landsidespreader is utilised. In thismode, the crane operatesas a conventional crane.

Figure 1. Dual spreader crane configuration

Lift type Description Conventional Dual Triple crane spreader spreader

crane crane

20 Single 20 ft 1-Retracted 1-Retracted 1-Retracted

40 Single 40 ft/45 ft 1-Extended 1-Extended 1-Extended

2x20 Twin 1-Extended 1-Extended 1-Extended

20_20 Two 20 ft side-by-side 2-Retracted 2-Retracted

2x20_2x20 Two twins side-by-side 2-Extended 2-Extended

2x20_40 Twin and 40 ft side-by-side 2-Extended 2-Extended

40_40 Two 40 ft/45 ft side-by-side 2-Extended 2-Extended

20_20_20 Three 20 ft side-by-side 3-Retracted

2x20_40_40 Twin and two 40 ft side-by-side 3-Extended

2x20_2x20_40 Two twins and 40 ft side-by-side 3-Extended

2x20_2x20_2x20 Three twins side-by-side 3-Extended

40_40_40 Three 40 ft side-by-side 3-Extended

Figure 2. Crane lift types

Figure 3. Triple-spreader crane configuration


40 • CONTAINER MANAGEMENT • August 2007

According to ZPMC, thecrane’s rated lifting capacity isas follows:

Pluses and minusesStrengthsThe cranes have asubstantially higher liftingcapacity than conventionalcranes and can handle morecontainers in a single liftcycle. Still, the hoisting speedremains the same and, despitethe fact that cycle elapsed timeis greater than for aconventional crane, terminaloperators report significantincreases in productivity.

Operational constraintsCertain requirements areimposed before a multi-spreader mode can be used.

Weight constraints: The 80-tonne and 120-tonne liftingcapacities allow cranes tohandle dual 40 ft and triple 40ft containers respectively, butdo not always allow multiplefull 20 ft containers to behandled. If the maximum grossweight for a 20 ft container is30 tonnes, than the ‘heavy lift’of four 20 ft containers willrequire a lifting capacity of 120tonnes under two spreaders,and six 20 ft containers willrequire 180 tonnes.

Stowage constraints:Multiple spreaders cannot beused if stowage is uneven, asthe containers have to belevelled and be in positionside-by-side to each other. For

instance, a dual spreader infour 20 ft container mode canbe used only when there arefour levelled 20 ft containersavailable to pick up.

Yard interface constraints:Multi-spreader operationrequires that multiple terminaltrucks are located under thecrane at the same time. Evenif the terminal operatingsystem dispatches multipletrucks to arrive at the sametime, there is no guarantee thatthey will arrive concurrently.Decoupled operations usingstraddle or shuttle carriers donot have this constraint.

OpportunitiesIncreased crane productivitysuggests that suchconfigurations can be usedefficiently for mega-vesseloperations that require a largernumber of containers to behandled from fewer numbersof bays.

Areas of concernIntroduction of the dual- andtriple-spreader crane raisessafety issues for the gear crewinspecting containers andhandling semi-automatictwistlocks (SATLs) from allfour corners of each container.To get to the corners, theworkers have to pass througha narrow corridor between twoterminal trucks.

Multi-spreader craneoperation can inducecongestion in the apron area,if the terminal is using trucksas prime movers. During

operation terminal trucks areoccupying multiple lanes andcan block traffic to othercranes.

Dual- and triple-spreadercranes create a higher wheelload. For example, a dual-spreader crane with eightwheels per corner creates 165tonnes of wheel load, 37.5%more than a conventionalcrane wheel load. This meansthat a complete engineeringassessment of the wharfsurface and rails is needed tomake sure that the cranedeployment is feasible.

A case studyVarious container terminalstatistics analyses use anumber of indicators tomeasure productivity ofcontainer cranes. For thisarticle we are going to use thegross crane rate indicator,which is defined as the totalnumber of containers handleddivided by the gross cranetime. The gross crane rate is ameasure of the productivity ofthe crane and terminaloperation as a whole, as alldelays under control of theterminal operator (operatingdelays) are included in thegross crane time.

According to ZPMC, adual-spreader crane “can boostproductivity by 50% if loadingand unloading techniques areimproved accordingly”. For atriple-spreader crane, ZPMCstates that: “Compared withthe twin 40 ft container cranes,its handling efficiency can beimproved by at least 15-20%”.

ZPMC also reports thatdual-spreader cranes at thePort of Dubai have created anew world record: 104 teu perhour. At the same time, whilemost ports report an increasein performance, their reportedproductivity rates vary. We

hope that by providinganswers to the followingquestions, a model will beprovided that can be used forimpartial estimation of craneproductivity in a variety ofoperational conditions.1. What maximum

(minimum) increase insustainable performanceshould we expect if wereplace the conventionalcrane with a dual- ortriple-spreader crane andperform a ‘typical’operation?

2. What sustainableproductivity can theterminal operator expectfrom the deployment of adual- or triple-spreadercrane instead of aconventional crane for aparticular vessel?

We hope that the article cananswer those questions andprovide a model that can beused for impartial estimationof the crane productivity in avariety of operationalconditions.

LimitationsCrane productivity depends ona number of factors, includingthe characteristics of theoperation, such as vesselstowage configuration; the teuto containers ratio; averagecontainer weights; containershandled in each task; etc. Inorder to estimate the general‘boost’ in productivity, we haveused the parameters of a‘typical’ operation for a middle-size post-Panamax vessel at theterminal with benchmarkingcharacteristics of the containerfleet. Results are therefore notuniversal and can be used forcomparison purposes only.

It has been known forquite some time in theindustry that the gross cranerate fluctuates significantly,

Dual-spreader crane Triple-spreader craneUnder single spreader 65 tonnes 60 tonnes

Under dual spreader 80 tonnes 100 tonnes

Under triple spreader 120 tonnes

Figure 4. Rated lifting capacity


August 2007 • CONTAINER MANAGEMENT • 41

even for terminals that havesimilar operating conditionsand identical cranes. Themodel presented here is notintended to predict exactproductivity figures; rather itestimates the ‘end points’ ofthe confident interval.

At any particular timeduring vessel operation, thecrane executes one of thefollowing tasks:

Task 1: unloading from the deckTask 2: unloading from the holdTask 3: loading to the deckTask 4: loading to the hold.

Each task has its ownspecifics and its owndistribution of operationaldelays. The differences arereflected in the productivitystatistics. Hence we willmodel each taskindividually.

Alexandre Goussiatiner is a container terminal andtransportation specialist with Sandwell Engineering Inc. inVancouver, Canada. The second part of this article will appearin the September 2007 issue of Container Management.

Sandwell Engineering Inc.Suite 600 - 885 Dunsmuir StreetVancouver, BC V6C 1N5 Canadael 604 630 7525 (direct)tel 604 684 9311e-mail: [email protected]

Model definitionContainers handledSuppose that during vessel operation the crane was involved in all four operational tasks:

Task 1 2 3 4Containers handled v1 v2 v3 v4

Then the total containers handled during the operation can be found as follows:

Total containers handled:

Loading spectrumSuppose that we have portioned all the crane cycles in a task into groups according to the number of containers handled in each cycle:

# Containers 1 2 n# Lifts s1 s2 sn

Then the loading spectrum of the crane, denoted by, is defined as follows:

Loading spectrum: S = {s1, s1, ...,sn}.

Elapsed time spectraSuppose that we have portioned all the crane lifts in a task into groups according to the number of containers handled in each liftcycle and then calculated average gross lift cycle time, measured in seconds, within each group:

# Containers 1 2 nAverage cycle time t2 t2 tn

Then the elapsed time spectrum of the crane, denoted by, is defined as follows:

Elapsed time spectrum: T = {t1, t1, ...,tn}..

Crane gross elapsed timeThe crane gross elapsed time for the whole operation can be defined as follows:

Crane gross elapsed time:

Crane gross rateThe crane gross rate is total containers handled divided by crane gross elapsed time.Then the crane gross rate, denoted by G, can be calculated as follows:

Crane gross rate: [cont/hr]

This formula is applicable for conventional cranes as well as for multi-spreader cranes. We assume that containers handled areknown, and now the question is how to determine load and time spectra.

4∑vii=1

n∑sjtij=1

4∑i=1

n∑sjtij=1

4∑i=1

4∑vii=1

3600


00 • CONTAINER MANAGEMENT • September 2007 September 2007 • CONTAINER MANAGEMENT • 00

To determineloadingspectra, aspecial cranesimulation

software system calledCraneSpectra has beendeveloped. CraneSpectra usesa physical model of a vesseland stowage and generatesdischarging and loadingsequences. The containers’stowage positions, theirstatus and weights arerandomised. During thesimulation the crane tries toselect moves with themaximum number ofspreaders. When this is notpossible, the crane‘disconnects’ spreaders, onlyto connect them again whensuch a move is allowed. Therecord of the cranemovement is used tocalculate load spectra.

The data presented inFigure 1 were used to simulatethe ‘typical’ operation.

The intermediate results ofthe CraneSpectra simulation

runs (data from 100 runs) arepresented in Figure 2. As canbe seen, CraneSpectra

recorded usage of all lift typesduring the runs anddetermined ‘average’

frequency for each lift type.Based on the recording,

CraneSpectra calculates the

In pursuit ofproductivity 2

In the final part of a two-part article, Alexandre Goussiatiner of Sandwell

Engineering Inc. concludes his investigation into productivity rates for multi-spreader

quayside cranes, compared with single-lift alternatives

Vessel capacityIn-hold rows 15

In-hold tiers 9

On-deck rows 17

On-deck tiers 6

In-hold capacity (teu) 3,000

On-deck capacity (teu) 3,300

20 ft bay to vessel capacity ratio 0.1

Containers handledHandled to capacity ratio 0.6

Teu to containers ratio 1.6

Full to total ratio 0.85

Weights 20 ft average gross weight (tonnes) 18

20 ft gross weight variation 0.7

20 ft average tare weight (tonnes) 2.3

40 ft average gross weight (tonnes) 24

40 ft gross weight variation 0.4

40 ft average tare weight (tonnes) 3.8

Figure 1: Typical operational dimensions



cranes’ loading spectra (seeFigure 3).

As can be seen, twocontainers at a time is theprevailing case for the double-spreader crane and threecontainers at a time for thetriple-spreader crane. Forcomparison, about 85% of alllifts performed byconventional cranes involveonly one container.

Elapsed time spectraWe assume that conventionalcrane gross rates for single-and twin-lift operations areknown from the terminalstatistics. We also assume thatthe operational conditions for

dual- and triple-spreadercranes (such as vesseloperational dimensions,container fleet, yardequipment, etc.) are equal tothose for the conventionalcrane. The purpose of this isto show how to estimateelapsed time spectra for dual-

and triple-spreader cranesusing comparative analysis.

Supposing thatcontainer/hour is the grossrate for the single lift andcont/hr is the gross rate forthe twin lift, then theelements of the elapsed timespectra can be calculated asfollowing:

t2= 3,600/ g2 sect2= 2*3,600/ g2 sec

For instance, if g2 = 30cont/hr (t2 = 120) and g2 = 40(t2 = 180), then conventionalcrane spectra are defined asfollows:

T= {120, 180}

Hoisting speed characteristics(see Figure 4) and liftingcapacity for all three types of

crane during single- and twin-lift operations are similar, sowe can conclude that the andparameters of the spectrumshould be the same for allcranes.

To estimate other elementsof the spectrum we shouldconsider two models: arealistic model (R-Model) andan optimistic model (O-Model).

R-ModelCertainly handling morecontainers in a single liftincreases the elapsed timeand it is reasonable to assumethat this is a quasi-linearfunction. The assumption isbased on the limitedmonitoring data and can bevalidated further when moredata become available. Theassumption allows us todetermine the lowerboundary of the ‘confidenceinterval’. It is unlikely thatproductivity can fall lowerthan the level defined by theR-Model.

O-ModelFor the ‘optimistic’ model,we assume that handlingmore than two containers atonce does not require moretime than it takes to performa twin-lift. The assumptionallows us to determine theupper boundary of the‘confidence interval’. It isunlikely that productivity canbe higher than the level

Figure 2: CraneSpectra simulation runs

Figure 3: Loading spectra

Lift Type Task 1 Task 2 Task 3 Task 4 Dual Triple Dual Triple Dual Triple Dual Triple

20' 10 0 12 0 12 0 10 0

40' 18 36 42 0 88 0 73 36

2x20' 16 3 12 3 14 0 13 0

20_20 94 12 84 0 84 0 94 12

2x20_2x20 64 3 57 2 57 0 64 0

2x20_40 0 9 6 0 4 0 3 9

40_40 360 9 312 7 290 6 331 9

20_20_20 0 58 0 60 0 60 0 58

2x20_40_40 0 0 0 5 0 6 0 0

2x20_2x20_40 0 0 0 0 0 0 0 0

2z20_2x20_2x20 0 42 0 40 0 42 0 45

40_40_40 0 225 0 216 0 216 0 225

Task Containers

1 2 3 4 5 6 Dual Spreader Crane 1 28 470 0 64 0 0 2 54 408 6 57 0 0 3 100 388 4 57 0 0 4 83 438 3 64 0 0 Triple Spreader Crane 1 36 24 292 3 0 42 2 0 10 276 7 0 40 3 0 6 276 6 0 42 4 36 21 292 0 0 45

Conventional Dual Spreader Triple Spreader Crane Crane Crane

Rated Load Hoist Speed

[m/min] 90 90 75

Empty Hoist Speed [m/min] 180 180 180

Trolley Speed [m/min] 240 250 240

Figure 4: Hoisting speed comparison table



defined by the O-Model. Based on these models,

we can estimate the elapsedtime spectra, as shown inFigure 5.

Modelling results

The elapsed time spectrum,which is based on thepremise that the gross cranerate for the conventionalcrane is 30 cont/hr for thesingle lift and 40 cont/hr forthe twin lift, was used toproduce the final modellingresults (see Figure 6).

Figure 7 representsmodelling results for thenumber of lifts counted duringthe vessel operation.

ConclusionsConservatively, terminal

operators should expect a26% increase in productivitywhen deploying a dual-spreader crane and a 38%increase when deploying atriple-spreader crane. Theincrease is indeed verysignificant. However, it doesnot mean that from now onwe can recommend only dualor triple cranes to bepurchased and deployed.Crane productivity is onlyone criteria of many that haveto be considered duringdecision-making.

Figure 5: Elapsed time spectra

Figure 7: Crane lifts counted for a typical vessel operation

Alexandre Goussiatiner is a container terminal andtransportation specialist with Sandwell Engineering Inc. inVancouver, Canada. The first part of this article appearedin the August 2007 issue of Container Management.

Sandwell Engineering Inc.Suite 600 - 885 Dunsmuir StreetVancouver, BC V6C 1N5 Canadael 604 630 7525 (direct)tel 604 684 9311e-mail: [email protected]

Dual Spreader Crane Triple Spreader CraneR-Model O-Model R-Model O-Model

Gross Crane Rate [cont/hr] 37.8 40.4 41.5 59.8

Increase over baseline 26% 35% 38% 99%

Gross Crane Rate [TEU/hr] 60.5 64.6 66.4 95.7

Figure 6: Gross crane rates

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