507
1 INTRODUCTION
Maritime container terminals are key elements of the
global transport network. Due to the necessity to
shorten the ship’s mooring time in the port and to
minimise transport and handling costs, port terminals
are becoming more efficient while transhipment
operations must be carried out quickly. For each ship
that comes to the port for service, the terminal earns
money. As one of the most important performance
measures is the turnaround time of ships in the port,
it is necessary to keep this time to a minimum [11].
Unlike other research that propose an optimisation
methodology for solving container handling problems
using different algorithms [5, 10, 13], this article
develops new formulas enabling the calculation of
times of individual operations that affect the
reloading of a container. Although some authors use
the network planning to investigate chosen aspects of
everyday port operations [4, 6], there are several
contributions of this paper. First, for the better
understanding of the processes taking place at
maritime container terminals, main reloading
operations are disaggregated in several elementary
activities. The vessel cycle time is analysed while
separately investigating the STS (Ship to Shore) crane
cycle time, the RTG (Rubber-Tyred gantry) cycle time,
as well as the IMV (Internal Movement Vehicle)
transfer time. Then, we propose mathematical
formulas for times of each operation influencing both
the unloading and then the loading of a container at
the maritime container terminal. Thus, it is possible to
analyse in detail individual reloading operations and
indicate those that can be further improved. Finally,
this work assumes that the elements of the PERT
The Determination of Times of Transhipment Processes
at Maritime Container Terminals
A. Bartosiewicz & A. Kucharski
University of Łódź, Łódź, Poland
ABSTRACT: Nowadays managers and decision-makers around the world seek every opportunity to lower costs
of the ship’s mooring time at seaports. In this article, main operations taking place at maritime container
terminals are first disaggregated in several elementary activities. Then the vessel cycle time is analysed while
separately investigating the STS (Ship to Shore) crane cycle time, the RTG (Rubber-Tyred Gantry) crane work
cycle time and the IMV (Internal Movement Vehicle) transfer time. A triangular distribution describes times of
each of the container handling stages while the PERT (Program Evaluation and Review Technique) method is
used to estimate the total time for all reloading activities. The paper demonstrates the proposed method
effectiveness with data of Baltic Container Terminal (BCT) Gdynia. The use of formulas developed for the
calculation of times of individual operations that affect the reloading of a container at maritime container
terminals enables an in-depth assessment of the effectiveness of the reloading processes. Thus, the proposed
tool gives terminal managers opportunity to track which stage of the container reloading consumes most time
and generates biggest costs.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 16
Number 3
September 2022
DOI: 10.12716/1001.16.03.13
508
(Program Evaluation and Review Technique) method
can be used to estimate the total time for all reloading
activities. Therefore, a triangular distribution with
parameters (to, td, tp) is used when each of the
considered stages would most likely take td seconds,
but not more than tp, nor less than tp seconds. The
method we propose is relatively simple, but it gives
satisfactory results that can successfully support
decision-making. It is also universal. Without
significant modifications, it can be used to optimise
the operation of different container terminals, with a
different layout of quays, storage yard, etc. Moreover,
in future research, it can be extended with PERT-LESS
cost-time model, thus allowing the determination of
the possibilities of potential time reduction for each
stage.
2 RESEARCH DESCRIPTION
2.1 Assumptions
Table 1 presents basic technical data of reloading
devices operating at the BCT Gdynia which were later
used to calculate the duration of reloading operations.
Table 1. Technical data of the equipment operating at the
maritime container terminal (Authors).
_______________________________________________
Equipment Parameters Technical
data
_______________________________________________
STS Winch trolley travel length 100 m
Lifting height from the wharf to ~ 35 m
the bottom of the winch spreader
Crane span 30 m
IMV Length 18.5 m
Width 3.0 m
Height 1.5 m
Maximum capacity 60 t
Maximum speed 7 m/s
RTG Crane travel length 135 m
Lifting height from the ground to 15 m
the bottom of the spreader
Crane span 20 m
_______________________________________________
We also assumed that containers were reloaded at
the BCT Gdynia at 32 sectors where RTGs were
placing 20-ft containers parallel to the quay in
7x22x/1–5/ (width x length x height) blocks. We than
assumed that at the described terminal, 2,402 40-ft
containers were reloaded, arranged on the ship as
follows: 24 containers along, 17 containers across and
up to 6 containers above. Four gangs were assigned
for the task, consisting of one STS crane, three RTGs,
five IMVs and employees necessary for the
implementation of operations at the quay and in the
storage yard.
2.2 Notations and parameters
The following notations and parameters are used
throughout the paper to model the container
reloading at the maritime terminal.
2.2.1 Times
L
H
t
or
l
h
t
adopted time needed for the load hooking
(3 s).
L
Li
t
or
l
li
t
time needed for the load lifting.
T
Lo
t
time needed for the winch trolley driving and the
load lowering
L
Lo
t
time needed for the load lowering.
L
U
t
adopted time needed for the load unhooking (10
s).
T
Li
t
time needed for the spreader lifting and the winch
trolley driving.
c
d
t
time needed for the crane bridge driving.
T
d
t
or
t
d
t
time needed for the winch trolley driving.
l
u
t
time needed for the load lowering and unhooking.
l
lo
t
time needed for the load lowering.
S
Li
t
or
s
li
t
time needed for the spreader lifting.
ct
d
t
time needed for the crane bridge and the winch
trolley driving.
S
Lo
t
or
s
lo
t
time needed for the spreader lowering.
2.2.2 Heights
Li
H
container lifting height to the bottom of the STS
crane traverse.
s
H
known height of the ship above the waterline
(12.5 m).
c
h
known container height (2.393 m).
sf
h
adopted safety margin for manoeuvring over the
last layer of containers (3 m).
L
Li
h
or
l
li
h
height of the load lifting.
IMV
h
known height of the IMV’s trailer (1.5 m).
L
Lo
h
or
l
lo
h
height of the load lowering.
s
lo
h
height of the spreader lowering.
2.2.3 Distances
T
d
s
or
t
d
s
travel distance of the loaded winch trolley.
c
d
s
travel distance of the crane bridge.
2.2.4 Phases
1
f
accelerated motion.
2
f
constant speed.
3
f
reduced speed.
2.2.5 Accelerations
L
Li
a
or
l
li
a
known acceleration for the loaded winch
(0.75 m/s
2
or 0.15 m/s
2
).
c
d
a
known acceleration for the crane bridge (0.2 m/s
2
).
L
Lo
a
or
l
lo
a
known acceleration for the load lowering
(0.75 m/s
2
or 0.15 m/s
2
).
T
d
a
or
t
d
a
known acceleration for the winch trolley
(1 m/s
2
or 0.4 m/s
2
).
S
Li
a
or
S
Lo
a
or
s
li
a
or
s
lo
a
known acceleration for the
unloaded winch (0.75 m/s
2
or 0.15 m/s
2
).
2.2.6 Speeds
LiL
v
or
lil
v
known accelerated speed of the load
lifting (1 m/s or 0.47 m/s).
LoL
v
or
lol
v
known constant speed of the load
lowering (1 m/s or 0.47 m/s).
HLoL
v
or
Hlol
v
adopted reduced speed of the load
lowering (0.25 m/s or 0.08 m/s).
dc
v
known accelerated speed of the crane bridge (2.17
m/s).
Hdc
v
adopted reduced travel speed of the crane
bridge (1.08 m/s).
509
dT
v
or
dt
v
known accelerated travel speed of the
winch trolley (3.5 m/s or 1.17 m/s).
Hdt
v
known reduced speed of the winch trolley (0.58
m/s).
pLi
v
or
lis
v
known accelerated speed of the empty
spreader lifting (2.5 m/s or 0.93 m/s).
los
v
known speed of the empty spreader lowering
(0.93 m/s).
HLoS
v
or
Hlos
v
adopted reduced speed of the empty
spreader lowering (0.25 m/s or 0.17 m/s).
2.2.7 Other
c
b
known container width (2.352 m).
c
l
known container length (5.898 m or 12.032 m).
k number of containers in layers/rows on the
ship/yard.
L adopted distance to the first container in the row
(15 m).
kSn number of yard sectors passed along the quay.
lS adopted length of the yard sector (150 m).
sn adopted straight-line distance from the quay to the
yard (20 m).
kRp number of rows passed in the storage yard.
bR adopted width of the yard row (18 m).
kSp number of sectors passed in the storage yard.
2.3 Calculations
The following paragraphs contain formulas used to
calculate times of the container unloading from the
ship on the IMV (1, 3–22), of transporting it from the
quay to the storage yard (34–35) and of unloading it
from the IMV by the RTG (2, 23–33). The formulas
were written out in detail for the first stages of the STS
work cycle only. All calculations are based on own
knowledge and observations made during study
visits to the BCT Gdynia as well as the literature of the
subject [3, 7–9, 12].
The specificity of the work of the STS winch trolley
[2] allows us to assume that the times of the container
unloading (T1) and loading (T6) at the quay can be
calculated in a similar way, as the sum of the
following components (1):
16
L L T L T S
H Li Lo U Li Lo
T T t t t t t t= = + + + + +
(1)
The total times of the container unloading (T3) and
loading (T4) in the yard may be determined similarly
(2):
34
l l c t l s ct s
h li d d u li d lo
T T t t t t t t t t= = + + + + + + +
(2)
2.3.1 STS crane work cycle
As shown in paragraph 3.2, times needed for the
load hooking (process A in Table 2) and unhooking
(process D) were adopted. The latter one is longer and
lasts 10 seconds because we also considered the time
needed for the container to be put on the terminal
vehicle waiting at the quay.
As regards other times of the STS crane work cycle,
first we must consider container lifting height to the
bottom of the STS crane traverse. It can be calculated
as the sum of known height of the ship above the
waterline, the height of the containers’ layers on the
deck, as well as adopted 3 metres safety margin for
manoeuvring over the last layer of containers:
Li s c sf
H H k h h= + +
(3)
We assume that all containers are un/loaded
from/to the ship’s deck, so the container is always
lifted, and the empty spreader is always lowered at 3
metres. Then, we may determine the time of the load
lifting (process B):
( ) ( )
12
LL
L
Li
Li Li
t t f t f=+
(4)
In the first phase (f1) the container is lifted to the
height
( )
1
L
Li
hf
, and in the second phase (f2) – to the
height
( )
2
L
Li
hf
. The sum of these two heights must
equal the adopted safety margin for manoeuvring
over the last layer of containers:
( ) ( )
12
LL
L
Li sf
Li Li
h h h f h f= = +
(5)
The height of the load lifting in the accelerated
motion may be determined if we know the
acceleration for the loaded winch, or the winch
maximum speed for the load lifting:
( )
( )
2
1
1
2
L
L
L Li
Li
Li
a t f
hf
=
(6)
( )
1
L
LiL
Li
L
Li
v
a
tf
=
(7)
Then, we may calculate the height of the load
lifting at constant speed, and later also the time
needed for the load lifting in the second phase:
( ) ( )
21
LL
L
Li
Li Li
h f h h f=−
(8)
( )
( )
2
2
L
L
Li
Li
LiL
hf
tf
v
=
(9)
Total time needed for the winch trolley travel and
the load lowering (process C), in turn, consists of two
partial times: the winch trolley travel time (
T
d
t
) and
the time needed for the load lowering (without the
winch trolley driving) (
L
Lo
t
). Therefore, we have
performed our calculations in two steps. First, we
calculated the winch trolley travel time:
( ) ( )
( )
1 2 3
T
TT
T
d
dd
d
t t f t f t f= + +
(10)
In the first phase (f1), the winch trolley travels the
distance
( )
1
T
d
sf
, in the second phase (f2) – the
distance
( )
2
T
d
sf
, and in the third phase (f3) the same
distance as in the first phase
( )
( )
31
T
T
d
d
s f s f=
. Once
again, in our calculations we may use the known
510
acceleration for the winch trolley and the known
maximum travel speed of the winch trolley:
( )
( )
2
1
1
2
T
T
Td
d
d
a t f
sf
=
(11)
( )
( )
13
T
T
dT
T
d
d
d
v
t f t f
a
==
(12)
Then, we may calculate the distance the winch
trolley has to travel at a constant speed:
( ) ( )
( )
2 1 3
T
TT
T
d
dd
d
s f s s f s f= − −
(13)
In the above formula, we assumed that total travel
distance of the loaded winch trolley may be
determined as the sum of the adopted 15 metres
distance to the first container in the row and the
overall width of the containers’ layer:
T
dc
s L k b= +
(14)
Considering all the above, the time needed for the
winch trolley to travel at a constant speed may be
calculated as follows:
( )
( )
2
2
T
T
d
d
dT
sf
tf
v
=
(15)
The load lowering begins after the winch trolley
has finished traveling. Total time needed for the load
lowering consists of three partial times. We must
remember that in the below formula times of the load
lowering in phases 1 and 3 are equal
(
( )
( )
13
)
L
L
Lo
Li
t f t f=
):
( ) ( )
( )
1 2 3
L
LL
L
Lo
Lo Lo
Lo
t t f t f t f= + +
(16)
The load is being lowered until it is placed on the
IMV waiting at the quay. The crane spreader height
from the ground may be calculated as the sum of
known heights of both the IMV’s trailer and the
container:
L
g IMV c
h h h=+
(17)
The adopted height of the load lowering is the
difference between the container lifting height to the
bottom of the STS crane traverse and of the IMV’s
trailer (
L
Lo Li IMV
h H h=−
), but at the same time we may
determine it as below:
( ) ( )
( )
1 2 3
L
LL
L
Lo
Lo Lo
Lo
h h f h f h f= + +
(18)
We assumed that
( )
3
3
L
Lo
h f m=
, and in next steps
we used formula 6 to calculate
( )
1
L
Lo
hf
and formula
9 to calculate
( )
2
L
Lo
tf
, as well as
( )
3
L
Lo
tf
. Then, we
may use the below formula to calculate the height of
the load lowering at a constant speed:
( ) ( )
( )
2 1 3
L
LL
Li IMV
Lo Lo
Lo
h f H h h f h f= − − −
(19)
When determining the time needed for the
spreader lifting and the winch trolley driving (process
E) we first determined the time needed for the
spreader lifting (
S
Li
t
), and then – for the winch trolley
travel time (
T
d Li
t
). The time needed for the empty
spreader lifting was calculated based on the following
formula:
( ) ( )
12
SS
S
Li
Li Li
t t f t f=+
(20)
In the first phase (f1), the empty spreader is lifted
to the height
( )
1
S
Li
hf
, and in the second phase (f2) – to
the height
( )
2
S
Li
hf
. Once again formulas 6 and 12
may be used in subsequent calculations together with
the below formula:
( ) ( )
21
SS
Li IMV
Li Li
h f H h h f= − −
(21)
The travel time of the winch trolley with an empty
spreader (
T
dS
t
), in turn, may be calculated similarly to
the travel time of the loaded winch trolley (10–15).
Yet, in this case the winch trolley should take the
container from the next row or tier on the ship.
Finally, the STS work cycle ends with the lowering
of the empty spreader from the adopted 3 metres
safety height on the container (process F). This again
takes place in two phases, in accelerated motion
( )
1
S
Lo
tf
and at a reduced speed
( )
2
S
Lo
tf
. Both times
may be determined according to the formulas 6, 9, 12,
and the formula presented below:
( ) ( )
21
SS
sf
Lo Lo
h f h h f=−
(22)
2.3.2 RTG work cycle
We determined reloading times in the storage yard
in a similar way as at the quay. The adopted time
needed for the load hooking (process A in Table 2) in
this case equals 3 seconds, while the time needed for
the load lifting (process B) is the sum of two
components:
( ) ( )
12
ll
l
li
li li
t t f t f=+
(23)
In the first phase, the container is lifted to the
height
( )
1
l
li
hf
, and in the second phase – to the
height
( )
2
l
li
hf
, while the spreader is always lifted to
the total height of 15 metres. In this case we used
formulas 5–9, as well as the formula considering the
height of the IMV’ trailer and of the container:
( ) ( )
21
ll
l
li IMV c
li li
h f h h h h f= − − −
(24)
Total travel time of the crane bridge (process C), in
turn, consists of three partial times:
( ) ( ) ( )
1 2 3
c c c
c
d
d d d
t t f t f t f= + +
(25)
511
During this time, RTG travels total distance which
depends on the place where the container is to be put
on the storage yard:
c
dc
s k l=
(26)
This distance consists of three distances which can
be determined based on the formulas 11, 13 and 15
and the assumption that
( )
32
c
d
s f m=
:
( ) ( ) ( )
1 2 3
c c c
c
d
d d d
s s f s f s f= + +
(27)
Total travel time of the winch trolley (process D) is
also the sum of three components:
( ) ( ) ( )
1 2 3
t t t
t
d
d d d
t t f t f t f= + +
(28)
In the first phase, the winch trolley travels the
distance
( )
1
t
d
sf
, in the second phase – the distance
( )
2
t
d
sf
, and in the third phase – the adopted 1 metre
distance
( )
3
t
d
sf
. Once again, to determine total
travel distance of the loaded winch trolley we used
the formulas 11, 13 and 15 together with the below
assumption:
t
dc
s k b=
(29)
The time needed for the load lowering and
unhooking (process E) consists of the time needed for
the load lowering (
l
lo
t
) and the time needed for the
load unhooking (
"l
u
t
). We assumed that the latter one
lasts 5 seconds. The lowering of the load begins when
the winch trolley travel ends. Thus, total time of the
load lowering consists of the following times:
( ) ( ) ( )
1 2 3
l l l
l
lo
lo lo lo
t t f t f t f= + +
(30)
In this case, the height of the load lowering is the
difference between the height of load lifting and the
product of the container height and the number of
containers plus one in layers/rows in the yard
( )
( 1 )
ll
lo li c
h h k h= − +
. Yet, this height may be also
calculated with the use of formulas 6, 9, 12, as well as
the below formula which assumes that
( )
3 1
l
lo
h f m=
:
( ) ( ) ( )
1 2 3
l l l
l
lo
lo lo lo
h h f h f h f= + +
(31)
The time needed for the empty spreader lifting
(process F) at the height equal to the height of the load
lowering may be calculated as below:
( ) ( )
12
ss
s
li
li li
t t f t f=+
(32)
In turn, to determine the travel time of the crane
bridge and the winch trolley (process G), we assumed
that except for the case when the crane bridge does
not move, the travel time of the crane bridge is longer
than the travel time of the winch trolley. Thus, total
operation time is influenced by total travel time of the
crane bridge. When the crane bridge does not move
(the travel time of the crane bridge equals zero), only
the travel time of the winch trolley affects total
operation time. As the travel speed of the crane bridge
and the winch trolley is independent of the load, at
this stage the formulas used previously to determine
the travel time of the crane bridge (25) and the travel
time of the winch trolley with the load (28) may be
also used.
The RTG crane work cycle ends with lowering the
empty spreader from the adopted height of 15 metres
onto the container. It takes place in three phases, in
accelerated motion
( )
1
s
lo
tf
, at a constant speed
( )
2
s
lo
tf
, and at a reduced speed
( )
3
s
lo
tf
. To
determine these times, we may use formulas
presented in this paragraph, as well as the below
formula which assumes that
( )
31
s
lo
h f m=
:
( ) ( ) ( )
2 1 3
s s s
l
li c IMV
lo lo lo
h f h h h h f h f= − − − −
(33)
2.3.3 IMV driving time
Finally, taking into account the way the terminal
vehicles travel along the storage yard and the quay,
adopted after Bartosiewicz [1], we calculated the
driving time of the IMV. We assumed that this time is
a product of the distance travelled by the IMV and
known speed of the IMV (
7
dIMV
m
v
s
=
):
dIMV dIMV dIMV
t s v=
(34)
We assumed that the distance travelled by the
terminal vehicle is a sum of such components as
number of yard sectors passed along the quay
multiplied by adopted 150 metres length of the yard
sector, adopted 20 metres long straight-line distance
from the quay to the storage yard, number of rows
passed in the storage yard multiplied by adopted 18
metres width of the yard row, as well as number of
sectors passed in the storage yard multiplied by
adopted length of the yard sector:
dIMV Sn S n Rp R Sp S
s k l s k b k l= + + +
(35)
2.4 Results
The paper demonstrates the proposed method
effectiveness with data of BCT Gdynia container
terminal. Based on our previous assumptions, the
formulas presented earlier and the information in
Table 1, in the next step we determined times for
individual operations, including unloading and then
loading of one container at the terminal in question. In
this case, we used a triangular distribution with
parameters (to, td, tp).
512
Table 2. The shortest (to), the most probable (td) and the
longest (tp) times (in seconds) for each operation comprising
the unloading and loading of one container at the terminal
(Authors).
_______________________________________________
Equipment Operation to td tp
_______________________________________________
Unloading
_______________________________________________
STS A. Load hooking 3 3 3
B. Load lifting
a
4 4 4
C. Winch trolley driving and load 34 48 60
lowering
D. Load unhooking 10 10 10
E. Spreader lifting and winch 16 25 33
trolley driving
F. Spreader lowering
a
12 12 12
_______________________________________________
IMV Transfer to the storage yard 37 74 131
_______________________________________________
RTG A. Load hooking 3 3 3
B. Load lifting
b
26 26 26
C. Crane bridge driving 0 36 66
D. Winch trolley driving 5 14 20
E. Load lowering and unhooking 28 38 49
F. Spreader lifting 7 12 17
G. Crane bridge and winch trolley 5 36 66
driving
H. Spreader lowering
b
20 20 20
_______________________________________________
Loading
_______________________________________________
STS A. Load hooking 3 3 3
B. Load lifting
a
17 25 32
C. Winch trolley driving and load 15 20 25
lowering
D. Load unhooking 5 5 5
E. Spreader lifting and winch 12 18 23
trolley driving
F. Spreader lowering
a
12 15 18
_______________________________________________
IMV Transfer to the storage yard 37 74 131
_______________________________________________
RTG A. Load hooking 3 3 3
B. Load lifting
b
8 19 29
C. Crane bridge driving 0 36 66
D. Winch trolley driving 5 14 20
E. Load lowering and unhooking 46 46 46
F. Spreader lifting 15 15 15
G. Crane bridge and winch trolley 5 36 66
Driving
H. Spreader lowering
b
12 17 22
_______________________________________________
a - all containers are unloaded from the ship’s deck, so the
container is always lifted, and the empty spreader is always
lowered at 3 m; b - the RTG lifts each container at 15 m, the
empty spreader is lowered from this height.
Then, using the PERT method, we estimated the
duration of individual reloading activities at the
described terminal (Table 3).
Table 3. Times (in seconds) of individual reloading
operations for one container handled at the analysed
terminal (Authors).
_______________________________________________
Equipment Operation Unloading Loading
_______________________________________________
STS Reloading a container 101.5±5.18 85.7±3.66
from the ship to the
IMV and vice versa
IMV Transfer to and from 77.3±12.60 77.3±12.60
the storage yard
RTG Reloading a container 183.5±15.67 184.2±15.67
from the IMV to the
storage yard and
vice versa
_______________________________________________
The average working time of the STS unloading a
container from a ship is approx. 102 seconds, and of
the STS loading a container, approx. 86 seconds. The
transport of a container by the IMV through the
terminal to or from the storage yard takes less than 78
seconds, while the transfer of a container by the RTG
takes an average of 184 seconds. Finally, to check for
the robustness of our results, we used the cumulative
distribution function of the standard Normal
distribution and performed the sensitivity analysis.
First, we indicated the directive term with 30 and 60
percent probability (Table 4). Then, we depicted
distributions for four described stages where the
dashed lines correspond to the deadlines for
completion in the schedules of both 30 percent and 60
percent probability scenarios (Figure 1).
Table 4. Times (in seconds) of individual reloading
operations for one container handled at the analysed
terminal (Authors).
_______________________________________________
Stage Schedule
30 percent 60 percent
probability probability
_______________________________________________
STS unloading 98.78 102.81
RTG unloading 175.28 187.47
STS loading 84.1 86.48
RTG loading 175.98 188.17
_______________________________________________
Figure 1. Cumulative standard Normal distribution for each
of the PERT models (Authors).
For the STS unloading, the directive term of the
container unloading may vary from 98.78 to 102.81
seconds. Shortening this time below the left end of the
range carries too high a risk of failure. On the other
hand, extending the time limit above the right limit
would unnecessarily extend this stage and inevitably
increase costs related to, inter alia, a longer stay of the
ship at the quay.
The expected values of directive terms are given
on the horizontal axis, and the cumulative
probabilities are on the vertical axis. In this way, we
may determine the chance of the implementation of a
given process for various scenarios, from those with
almost zero to those with almost 100 percent
probability.
513
3 CONCLUSIONS
In this article we propose formulas to analyse in detail
individual reloading operations and indicate those
that can be further improved. In particular, the
proposed approach allows to determine in which
cycle (STS crane work cycle, RTG work cycle, IMV
transfer cycle) there are the most delays, the
elimination of which may lead to a reduction in the
transhipment time, and thus the ship’s berthing time
in the port. This is particularly useful for decision-
makers and terminal operators who are interested,
inter alia, in identification of bottlenecks during the
container handling, as well as in optimisation of
processes taking place in seaports.
Our results show that most time-consuming
activities during the unloading include transfer to and
from the storage yard (IMV transfer time), driving the
trolley and lowering the load (STS cycle), or driving
the gantry and the winch trolley (RTG cycle). It also
appears that during the loading of one container at
the terminal, managers should pay special attention to
such aspects as the IMV transfer time, or the time that
the STS and the RTG need to lift, lower, and unhook
the load. At the same time, the sensitivity analysis we
performed proves the accuracy of estimations of the
duration of activities that constitute each of the stages.
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