Impact of Port Clearance on shipping Safety, Energy Consumption and Green Ports Sustainability

Abstract

In many ports, the ship's speed is limited for the safety of navigation. At the same time, ship captains and port pilots choose the speed of the ship, but not higher than the permitted speed of the ship in the port, therefore the speed of the ship also depends on the experience of the ship captains and port pilots and the sailing conditions of the ship in specific conditions. Choosing the optimal speed of ships in port, including the effect of shallow depth, can reduce fuel consumption and ship emissions in ports, which is important for the development of green and sustainable ports. In all cases, shipping safety is the highest priority. The main objectives of the article are determining the optimal speed of ships in ports with low clearance, ensuring navigational safety, reducing fuel consumption and emissions, and at the same time creating a sustainable port. The article presents the methodology of optimal ship speed calculation, minimum ship controllable speed maintenance, fuel consumption and emission reduction methodology and their impact on sustainable and green maritime transport and port development. The developed methodology was tested on real ships and with the help of a calibrated simulator, sailing through harbor channels and harbor waters in low clearance conditions.

Full text

Article Not peer-reviewed version
Impact of port clearance on
shipping safety, energy
consumption and green ports
sustainability
Vytautas Paulauskas * , Viktoras Sen
č
ila , Donatas Paulauskas , Martynas Simutis
Posted Date: 28 September 2023
doi: 10.20944/preprints202309.2004.v1
Keywords: maritime safety, energy efficiency, green and sustainable port, ships safety, environmental
impact, emissions
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Article
Impact of Port Clearance on shipping Safety, Energy
Consumption and Green Ports Sustainability
Vytautas Paulauskas 1, *, Viktoras Senčila 2, Donatas Paulauskas 3 and Martynas Simutis 4
1 Marine Engineering Department, Klaipeda University, H. Manto 84, LT-92219, Klaipeda, Lithuania;
vytautaskltc@gmail.com (V.P.)
2 Marine Engineering Department, Klaipeda University, H. Manto 84, LT-92219, Klaipeda, Lithuania;
Viktor.Sencila@ku.lt (V.S.)
3 Marine Engineering Department, Klaipeda University, H. Manto g. 84, LT-92294, Klaipeda, Lithuania;
paulauskasd75@gmail.com (D.P.)
4 Marine Engineering Department, Klaipeda University, H. Manto 84, LT-92219, Klaipeda, Lithuania;
martynas.simutis@gmail.com (M.S.)
* Correspondence: vytautaskltc@gmail.com (V.P.).
Abstract: In many ports, the ship's speed is limited for the safety of navigation. At the same time, ship captains
and port pilots choose the speed of the ship, but not higher than the permitted speed of the ship in the port,
therefore the speed of the ship also depends on the experience of the ship captains and port pilots and the
sailing conditions of the ship in specific conditions. Choosing the optimal speed of ships in port, including the
effect of shallow depth, can reduce fuel consumption and ship emissions in ports, which is important for the
development of green and sustainable ports. In all cases, shipping safety is the highest priority. The main
objectives of the article are determining the optimal speed of ships in ports with low clearance, ensuring
navigational safety, reducing fuel consumption and emissions, and at the same time creating a sustainable port.
The article presents the methodology of optimal ship speed calculation, minimum ship controllable speed
maintenance, fuel consumption and emission reduction methodology and their impact on sustainable and
green maritime transport and port development. The developed methodology was tested on real ships and
with the help of a calibrated simulator, sailing through harbor channels and harbor waters in low clearance
conditions.
Keywords: maritime safety; energy efficiency; green and sustainable port; ships safety;
environmental impact; emissions
1. Introduction
Sustainable and green ports are very important for all regions of the world and it is necessary to
achieve this in various possible ways. At the same time, it is necessary to understand that maritime
transport is very stagnant, for example, ships are planned to work for 15-20 years and reconstruction
or renovation is not always possible to use new types of fuel or new energy sources. At the same
time, even small progress in reducing environmental impact is important.
The entry of ships into ports is a daily procedure, but at the same time, the different experience
of ship captains and port pilots, different characteristics of ship manoeuvrability, traditions and other
elements greatly influence the amount of ship manoeuvres entering and leaving ports, fuel
consumption and generated emissions. The analysis of main engine manoeuvres of ships entering
ports shows very large differences between ships of the same type and it is mainly related to the
knowledge, experience and individual characters of ship captains and port pilots [1-3]. In many ports,
port pilots worked for a long time as navigators and captains on relatively small ships before
becoming pilots [4, 5]. As pilots become more competent, they receive permits to service larger
vessels, but the long working time on smaller vessels greatly affect their working methods.
A very good understanding of the ship's manoeuvrability by the ship's captain and port pilots
allows to guarantee the ship's navigational safety when entering ports and other places [2, 6], as well
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2
as to optimize the ship's manoeuvres and thereby reduce the ship's fuel consumption and emissions
generation [7, 8].
The analysis of accidents and incidents when ships enter the port showed that they are mostly
related to the mistakes of ship captains, port pilots or VTS (vessel traffic system) operators, but very
rarely ship accidents and incidents are related to the ship’s speed in port channels and port waters
[1, 3]. Many ports have speed limits for ships and in most cases these limits are between 6 and 10
knots [3, 9, 10].
In some situations, ship captains and port pilots, due to a lack of information about the ship's
manoeuvrability or lack of experience, did not take into account the technical and manoeuvrability
parameters of the ships, which affected the ship's behaviour at low clearances (spaces between the
ship's keel and the channel bottom), which led to ship manoeuvres errors, especially when ships
navigate the bends of navigational channels [3, 11]. It should be noted that in cases where professional
training and practical staff training is based on modern knowledge of ship manoeuvrability under
various navigational conditions, it can increase the navigational safety of ships entering and leaving
ports when ships sail independently and/or with the additional use of external assistance (e.g. port
tugs) or without it [12-14].
The optimal of ship’s speed in the ports entrance and internal navigation channels, assessing the
manoeuvrability of ships, has not been well studied, so the available experience of ship captains and
port pilots is often relied on, but such solutions are not always optimal [15, 16].
The main objective of the paper is to present a developed methodology to determine the optimal
ship speed in low clearance conditions, during which the ship is still well controlled, with minimum
fuel consumption and minimum ship emissions, which is very important for the development of
sustainable and green ports. The novelty of the article is based on the development of a methodology
that allows the calculation of the minimum ship's controllable speed, using minimum fuel
consumption and generating minimum ship emissions, depending on the size of the clearance (in the
case of low clearance).
The research methodology is based on the assessment of external and internal forces and
moments acting on the ship while sailing in port channels and port waters, determining the minimum
controllable ship’s speed, with small clearances and possible minimum fuel consumption, adapting
to specific port conditions and at the same time generating minimum emissions.
The main goal of low-clearance optimization is the safety of navigation in port shipping channels
with minimal fuel consumption and minimal ship emissions, which is essential for the development
of sustainable and green ports.
The article presents a method for calculating the optimal ship’s speed in port navigation
channels and port water areas, which are important for many ports, using the minimum fuel
consumption, and its application in specific conditions, which allows guaranteeing navigation safety
in ports, optimize fuel consumption, reduce emissions from ships, research results. The article
consists of the research analysis of the existing situation, the principles of creating a mathematical
model and the mathematical model itself. The application of the developed mathematical model in
specific conditions, the results of experiments performed on real ships and using a calibrated visual
simulator are presented. It also presents the discussion and conclusions of the calculated and
experimentally verified results of optimal ship’s speed in port navigation channels and port waters,
using minimal fuel consumption.
The scientific contribution of the conducted research is a new methodology that allows
determining the optimal speed of ships in port channels and port waters with minimal fuel
consumption and minimal impact on the environment, which is important for the development of
sustainable and green ports.
2. Analysis of ships sailing speed and generated emissions in ports situation and literature
review
Numerous resources have analysed vessel speed in harbours and inland waterways [2, 10, 17,
18]. Ship speed in ports is limited by the hydrodynamic effect of ship interaction (floating and
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3
mooring at quays), as well as waves caused by moving ships, which erode shores and negatively
affect (destroy) port infrastructure [15]. . Reduced ship speed also reduces the probability of ship
collisions [13, 17, 19 - 22]. For example, in the port of Klaipeda the permitted speed of the ship is up
to 8 knots [9], in the access channels of the port of Hamburg (in the Elbe river) up to 13 knots, in the
port areas up to 9 knots. (some places have special requirements when approaching individual port
locations and individual inland navigation for canal sections) [23]. Vessel speed limits are up to 12
knots in the canals of the port of Rotterdam, up to 8 knots in some sections [24]. Similar permissible
ship speeds can be found in other ports of the world [13, 18, 19, 21]. At the same time, the allowed
speed of ships in ports is often not optimal in terms of energy (fuel) consumption and emissions of
ships [16, 25]. For a sustainable approach, it is very important to find optimal ship speed solutions
when entering the port and in the internal shipping channels, as well as approaching individual
important points of the port (areas defined by port administrations) [19]. Reduced ship speed is also
important in reducing ship energy (fuel) consumption and emissions [25, 26].
After analysing ship accidents and emergency incidents in ports, it became clear that most of
them were caused by either too high or too low speed in ports [1, 3, 8, 13, 20], therefore, in determining
the optimal but at the same time safe speed of the ship in ports, the minimum possible the speed of
ships in ports is very important both from the point of view of the safety of shipping and the impact
on the environment [7, 15].
After assessing the main aspects of ship navigation in port channels and port waters (navigation
safety is a priority), they can be grouped as follows [20, 27, 28]:
- ship navigation must be safe for the sailing ships themselves;
- the passage of ships must not reduce the safety of other ships sailing in channels or moored at
quays;
- ship navigation must meet the general needs of the port (ship sailing schedules, positioning of
ships, minimal interaction with other ships entering and leaving the port);
- minimal impact on port infrastructure and superstructure;
- use the minimum fuel consumption;
- emit as little pollutants as possible during navigation.
Navigation of ships in port channels and port waters must be safe for the ship itself, and its
speed must allow good controllability of all operations entering the port (navigating through
channels, turning in turning basins, stopping, approaching and leaving quays) [21, 29]. In this way,
the ship's controllability is very important in the whole process of the ship's entry into the port.
When a ship is sailing through port channels and port water areas, it must not create impact for
other ships due to the high hydrodynamic interaction between ships, the impact of create by sailing
ship waves on berthing or passing ships as well during sailing clause to other constructions [28, 30].
Ports are sometimes very congested and ships sailing to and from the port must not create additional
time wasting for other ships and port operations [13, 17, 19, 31]. In many ports, the harbour
approaches and especially the inner navigation channels are not very busy, so ships have the
opportunity to sail at minimal but safe speeds, with minimal fuel consumption and at the same time
generating minimal emissions.
When sailing through port channels and port water areas, ships must not cause negative
consequences or additional risks to the port infrastructure and superstructure due to the waves
caused by the sailing ship or the risks of collision with the port infrastructure or superstructure [25,
28, 31, 32].
It is very important for ships to use as little fuel as possible when sailing through port channels
and port waters, which is very important for the economic indicators of the ship itself, and at the
same time generate minimal emissions in the port area, while positively influencing the creation of
green and sustainable ports [15, 33-35].
The above-mentioned factors are very important, but they partially contradict each other, as for
example, a very low speed of the ship in the port channels and port waters, as long as the ship is well
controlled, increases the safety of the ship, reduces the hydrodynamic impact on other ships, but at
the same time requires more time and it worsens port indicators, because other ships have to wait, in
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4
some cases they have to stop loading operations for a longer period of time, etc. [25, 33]. Many ports
have installed modern navigation systems that allow for high-quality regulation of ship traffic, but
they cannot accurately assess the minimum speed of control of ships, which is very important for
ensuring the safety of navigation in port channels.
Much attention is paid to the planning of port navigational channels and water areas in order to
meet the safety requirements of shipping navigation [33, 36-39], but in old and sometimes newly built
ports it is not always possible to fulfil all the requirements (standards and recommendations) due to
geographical and other conditions, for example, existing cities, protected historical objects, etc. As,
for example, in Helsinki, Haugesund and other ports in similar geographical situations, the
navigational channels are located between islands with historical structures and it is very difficult or
impossible to implement channel width standards or recommendations [18, 36, 37]. In this case, to
guarantee the safety of shipping, restrictions regarding wind speed and direction, requirements for
the use of tugboats and the like must be adopted [12, 22], so it is not always possible to use the optimal
calculated conditions.
Existing environmental requirements and recommendations, especially for ship emissions [40-
42], target ship operators to reduce fuel consumption and emissions at the same time, but this is not
always possible to achieve as the priority is navigational safety. In the event that ship captains and
harbour pilots, due to insufficient research on the manoeuvrability of the ship in specific conditions
or lack of knowledge and practical experience, doubt the possible minimum ships speed, they always
choose a speed that seems safe to them and often it is higher than the optimal speed [19, 31].
The minimum speed of the ship at which it can navigate the harbour channels and harbour
waters must be such that the ship can be well controlled, especially when braking the ship at turning
basins or approaching quays, depending on external forces [22]. In such cases, vessels must use
rudder-propeller assemblies and thrusters, if available on board, or use tug(s) to maintain good
control of the vessel. The minimum possible ship speed, when the ship is still well controlled, has
been analysed in various literature sources [43-45], but the minimum ship speed has been little
studied at shallow depths, which are typical for ports. At the same time, the minimum controllable
speed of the ship when sailing the ship in the navigation channels of the ports is especially important
in extreme hydro meteorological conditions, when it is very difficult to correct even the smallest
inaccuracies in the control of the ship.
Many studies deal with the problem of the schedules of ships navigating the harbour channels
and harbour waters [31]. Given the uncertainty of the arrival time processes of container ships and
other liners at large container ports and other similar ports and terminals, modelling capabilities are
often used. Separate works identify the main navigational processes and operations related to the
port's marine infrastructure and review and evaluate existing port modelling methods [12, 25]. The
indicated studies are for port assessment purposes with a focus on safety and capacity. The
evaluation of various similar models focuses on determining the appropriate criteria for ship
navigation based on what processes are included in each model and how they have been taken into
account in each model, but many models are incompletely related to the optimal ship speed in
harbour channels and harbour waters by estimating minimum fuel consumption and minimum
emissions [43, 47-49].
The analysis of previous theoretical and experimental works by various authors allows to
partially solve the practical problems of shipping safety and reducing environmental impact in ports,
but at the same time, new challenges are very important, because ports try to attract ships of the
maximum possible sizes, to reduce environmental impact as much as possible, i.e. to become green
and sustainable ports, therefore further research is essential.
The literature analysis carried out on the topic analysed in the article showed that a number of
studies have been carried out, but at the same time, there is a lack of complex studies related to the
minimum ship controllable speed, optimal fuel consumption when ships sail in ports, opportunities
to minimize the amount of ship emissions while sailing at an optimal speed, at low clearances in
harbour channels and harbour waters, what constitutes the novelty of these studies presented in the
article.
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In this way, the article analyses the minimum speed at which the ship can be operated using
minimum fuel consumption in port conditions, where there is little or in some cases the minimum
possible clearance is important both to provide navigational safety and to reduce environmental
impact, and this problem has been studied very little in detail.
In this way, there is a need to study the optimal ship’s speed in port channels and water areas
in order to optimize the ship’s speed in ports, minimizing fuel consumption and minimizing
generated emissions, which is influence on sustainable and green ports development and in same
time guaranteeing the necessary navigational safety of ships.
3. Research methodology
The following steps of research methodology were used to conduct the research (Figure 1). After
conducting the situation analysis and literature review, the mathematical model has been developed.
Figure 1. The algorithm of the research methodology.
3.1. Research methodology basic ideas
In order to prepare the methodology, first of all, an analysis of the available situation and
literature was carried out, which allowed an overview of the situation of ship control of ships entering
ports, including navigation safety, using the necessary fuel and the influence of shallow depth on the
sailing characteristics of ships. The movement of ships in port channels and port waters, the reduction
of emissions from ships in port channels and port waters, etc., were also studied. The necessary data
were collected based on literature sources and observations of real ship sailing conditions in port
channels and port waters, as well as experimental data obtained from VTS (vessel traffic system)
systems operating in ports, shipping companies and using calibrated full-mission simulators.
In this way, the methodology developed in the study must take into account the possible
attraction of the largest ships to the ports, the parameters of the port channels and the port water
area, the manoeuvrability of ships, fuel consumption, the effect of shallow water, hydrological and
hydro metrological conditions in the ports, as well as the possible minimum speed of ships in the
port navigation in the channels and in the port areas, guaranteeing the navigational safety of ships
(Figure 1).
Hydro-meteorological and hydrological conditions during navigation of ships in port channels
and port waters, which must be evaluated when developing research methods, are the following:
wind speed, wind course angle, current speed, current course angle, etc.
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Additional data needed for research and must be collected and analysed, such as: the width of
navigation channels (waterways), depths in port navigation channels and port water areas intended
for ship navigation and manoeuvring [50]. In addition, the relevant calibration coefficients of the
simulator obtained during theoretical and experimental studies [51-53] were taken into account.
On the basis of theoretical and experimental research, a mathematical model was created that
allows to calculate the possible minimum and optimal ships speed in the port channels and in the
port water area with the possibility of good control of the ship, the sailing time of the ships, fuel
consumption, emissions, as well as evaluating the hydrological and hydro meteorological conditions
in the port channels and the port in water areas. This model considers the implementation of the
following steps:
- collect and analysis of the aforementioned data,
- plan possible sailing distances in the port,
- calculate the minimum ship’s speed in real harbour conditions, based on the collected
necessary data,
- calculate of specific ship sailing parameters: speed, time, costs and fuel consumption;
- calculate and analysis of the total amount of emissions while the ship is sailing in the port
channels and in the port water area at optimal speed;
- make conclusions and recommendations on specific conditions.
The boundary conditions of the methodology and the model are as follows: the sizes of ships
and their sailing speed in the port channels and in the port water area depend on the infrastructure
parameters; the minimum ships speed depends on the external impact forces (wind, current, waves)
and clearance in case of good ship controllability; optimal ship speed is due to ship control
limitations; tugboat assistance is available to improve vessel handling.
The proposed methodology was verified based on a case study. The possible ships speed which
draft to depth ratio was up to 0.92 - 0.96 were analysed in detail, and calculations were made based
on the real data. Based on the archived results, recommendations, discussions and conclusions were
proposed regarding possible minimum ships speed in harbour channels and harbour waters, with
the lowest emission estimates. At the same time, the proposed methodology can be applied in other
ports as well.
3.2. Mathematical model
Many ports in the world have long approach and internal navigation channels in which ships
can keep optimal speed. External forces and moments acting on the ship sailing by port navigational
channels and port waters shall be compensated by ship’s rudder created forces and moments or if
use tugs assistance – created by additional tugs forces and moments. Thus, calculation of the forces
and moments can be done using the following mathematical model, based on D’Alembert principle
[22, 39, 54]:
Bandyti dar kartą
Bandoma iš naujo...
Bandoma iš naujo...
... 0
in k p N a c b sh T tug
XXXXXXXXXXX
β
++++ ++++ ++ +=
(1)
... 0
in k p N a c b sh T tug
YYYYYYYYYYY
β
++++ ++++ ++ +=
, (2)
... 0
in k p N a c b sh T tug
MMMMMMMMMMM
β
++++ ++++ ++ +=
, (3)
Where: ,,
in in in
X
YM- inertia forces and the moment; ,,
kk k
X
YM
- forces and moment created by
the ship’s hull, could be calculated by using the methodology stated at [51, 53]; ,,
X
YM
β
ββ
- the
ship’s hull as the acting “wing” related forces and the moment, could be calculated using the
methodology stated at [14]; ,,
p
pp
X
YM - forces and the moment created by the ship’s rudder or other
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steering equipment [51, 53]; ,,
NN N
X
YM - forces and the moment created by thrusters [22, 53];
,,
aa a
X
YM
- aerodynamic forces and the moment, could be calculated using the methodology stated
at [51, 53, 54]; ,,
cc c
X
XM
- forces and the moment created by the current, could be calculated using
the methodology stated at [51, 53]; ,,
bb b
X
YM
- forces and the moment created by waves, could be
calculated using the methodology stated at [51, 53]; ,,
s
hsh sh
X
YM
- forces and the moment created by
shallow water effect [22, 55]; ,,
TT T
X
YM- forces and the moment created by ship’s propeller
(propellers), could be calculated using the methodology stated at [51, 56]; ,,
tug tug tug
X
YM
- forces
and moment created by tugs [22, 51]. Additional forces and moments could be created by anchor or
mooring ropes or other factors.
When a ship is moving through port navigation channels and port waters (typical procedures
for ships entering ports) and without the assistance of tugboats, the ship's rudder forces and moments
must be able to compensate for all external forces and moments to keep the ship on a specific heading.
Then equations (1) – (3) could be written as follows:
...
in k a c b sh T p
X
XXXXXX X X
β
++++++ ++= (4)
...
in k a c b sh T p
YYYYYYYY Y
β
++++++ ++= (5)
...
in k a c b sh T p
M
MMMMMM M M
β
++++++ ++= (6)
Forces and moments expressed in equations (4) – (6) could be calculated using methodologies,
presented in [14, 51, 53, 55] and others.
When sailing in port navigation channels and port waters, there are often no waves, when a
ships speed of 6 knots and more, the ship's control is not affected by tugs and steering devices
(thrusters), and only traditional ship steering devices (ship propeller(s) and rudder(s)) are used to
control the ship. In such most cases, the ship sails with no or minimal drift angle and the ship's speed
does not change significantly (if the power of the ship's main engine(s) does not change), then
dependencies (4) - (6) will be written:
...
pkacshT
X XXXX X=+++ ++
(7)
...
pacT
YYYY=+++
(8)
...
pacT
MMMM=+++
(9)
Equations (7) - (9) are adapted to port conditions when there are no waves and the ship moves
straight or in small turns and does not require the use of additional ship control devices: tugs and
steering devices, like thrusters. In this case, the equations do not take into account the effects of waves,
forces and moments created by tugs and thrusters. In each specific case, equations (4) - (6) must be
adapted to the specific situation of the sailing ship (specific port).
Forces and moment created by rudder (rudders) ( ,,
p
pp
X
YM), acting on ship’s steering, could be
calculated as follows [22, 51, 53, 56]:
2
2
pxp
X
CSv
ρ
=; (10)
2
2
pyp
YC Sv
ρ
= ; (11)
p
pp
M
Yl=, (12)
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Where: ,
x
y
CC
- rudder hydrodynamic coefficients, could be taken in account until rudder turn
angle up to 20 degrees (to have steering reserve) [22, 57, 58]; v - ship’s speed;
ρ
- water density;
p
S - the area of projection of the rudder plane into the diametrical plane (area) [39, 53, 57];
p
l -
rudder’s transverse force shoulder [39, 53, 57].
The lateral (lift) force generated by the ship's steering mechanism, depending on the angle of
rotation of the rudder feather on shallow waters, can be calculated using the following formula:
2
2
py p w
YC Svk
ρ
=⋅⋅⋅⋅
, (13)
Where: w
k - turning velocity coefficient as the effect of shallow water factor [22, 54, 55].
In port channels and water areas, the ship will be steered without external help (tug) until the
moment created by the rudder (assessing the ship's controllability reserve) is greater than or equal to
the moments created by external forces, i.e. [22, 48, 53, 59]:
...
pacT
MMMM≥+++
, (14)
Aerodynamic forces and the moment ( ,,
aa a
X
YM
), could be calculated using the methodology
presented in [51]. Aerodynamic moment could be calculated as follows [51]:
2
1
0
()(sin)
2
aa x aa a
M
CSxxvq
ρ
=⋅⋅⋅ + ⋅⋅ , (15)
Where: a
C - aerodynamic coefficient, for the calculations could be taken between 1.07 – 1.30
depends of the ships architecture [51, 53]; 1
ρ
- air density, for calculations could be taken 1.25 kg/m³;
x
S - the space of projection onto diametrical plane (DP) of the wind surface area of the ship [39, 50,
53]; a
x
- abscissa of centre of gravity of aerodynamic force, can be calculated by methodology,
presented in [22, 39, 53, 57]; a
v - wind velocity; a
q - wind course angle; 0
x
- abscissa of the ship’s
turning pivot point [57], can be calculate as follows:
01 2
0()
o
ab
xx x
TT
xLk k k
L
α
−
=+ −⋅
, (16)
Where: L - ship’s length between perpendiculars; 0
x
k - abscissa coefficient, for many type of
ships is between 0.3 – 0.4; 1
x
k - abscissa coefficient depends of the ship’s draft differences, for many
type of ships is between 11.0 – 12.0; 2
x
k - abscissa coefficient depends of rudder turn angle, for many
type of ships is between 0.004 – 0.0045; a
T - ship’s astern draft; b
T - ship’s bow draft; o
α
- ship’s
rudder turn angle in degrees.
Current moment could be calculated as follows [51, 53]:
2
0sin
2
cc c c
M
CLTvxq
ρ
=⋅⋅⋅⋅⋅⋅ , (17)
Where: c
C - current hydrodynamic coefficient, for many type of ships could be taken between
1.2 – 1.5 (1.5 is for double propeller and ships with bulb); T - ship’s average draft; c
v - current
velocity; c
q- current course angle.
Ship’s propeller(s) creating moment could be calculated as follows [22, 51, 53] (in case of twin
propellers with different turning sides, this moment is equal to zero):
'24
10
()sin
2
Tprpr pr
L
MK nD x
ρ
α
=⋅⋅ ⋅ + ⋅ , (18)
Where: 1
'
K
- propeller’s coefficient, for many type of conventional propellers could be used
for calculations as 0.2 (more accurate coefficient could be taken from propeller’s specification);
p
r
n -
rotation frequency of the ship's propeller, 1
s
−;
p
r
D
- ship’s propeller diameter;
p
r
α
- the deviation
angle of the propeller flow, for conventional propellers is from 2 to 4 degrees, about 3 degrees can be
accepted in the calculations [22, 39, 53].
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Ship’s rudder(s) creating moment could be calculated as follows [22, 51, 53]:
2
0
()
22
py p w
L
M
CSvk x
ρ
=⋅⋅⋅⋅⋅+ , (19)
Finally, ship’s minimum steering speed in navigational channel could be calculated as follows:
0
2( ...)
()
2
acT
yw
MMM
vL
CSk x
ρ
+++
=
⋅⋅⋅ ⋅ +
, (20)
When sailing a ship in port navigational channels and water areas, it is very important that the
ship is well controlled and at the same time its speed is such that the fuel consumption is minimal.
The power of the ship's main engine and the relative fuel consumption can be expressed in a graph
obtained by analysing relevant data from literature sources [60-63] and experimental data obtained
on real ships (Figure 2).
Figure 2. The relative fuel consumption coefficient of a ship's engine ( '
k
qΔ), depending on the
relative power of the ship's engine(s) ( '
N).
The relative power of the ship's main engine(s) and the ship's relative speed can be expressed
by the following expressed on Figure 3 [29, 53, 62, 64]. The power of the engine and the speed of the
ship are related by a quadratic relationship [57, 66]. In most cases, the relative power of the ship’s
engine(s) and the ship’s speed can be used. For this purpose, a graph based on the experimental
results from more than 1000 ship passages can be used [53, 54, 61] (Figure 3).
Figure 3. The relative speed of the ship ( '
v) as a function of the relative power of the ship's engine(s)
('
N).
A limitation of the graph (Figure 3) with a very high overall hull fullness factor (δ) is that with
the overall fullness factor of the ship’s hull greater than 0.9, the form resistance parameters of the
ship’s hull shape change significantly and the accuracy of the graph is not good enough (error size
can reach more than 10 percent) [54].
On Figure 3 is the relative power of the ship's engine(s), could be calculated as follows [14]:
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'
n
N
NN
= , (21)
Where: N - the current power of the ship's engine, while the ship is sailing at speeds v; n
N -
nominal power of the ship's main engine(s).
On Figure 3 the relative ship’s speed '
v is calculated as follows [51]:
'
0
v
vv
= , (22)
Where: 0
v - the ship's speed at the rated power of the ship's engine(s).
Many harbours have limited depths, and with a small clearance between the ship's hull and the
bottom of the navigation channel, the added water mass increases and, at the same time, the
resistance of the ship's hull increases. The decrease in ship speed at low depth can be calculated using
the following formula [22, 55]:
11
'
11
1
1
S
k
vv k
+
=⋅ + , (23)
Where: S
v- ship’s speed in shallow water; v - ship’s speed in deep water; '
11
k - attached
water mass coefficient in shallow water; 11
k- attached water mass coefficient in deep water.
Added water mass coefficients in deep and shallow waters could be taken from graph (Figure
4) [22].
Figure 4. Dependences of the added water mass coefficient '
11
k on the T/H ratio and the ship's
sailing speed v.
The added mass of water depends on the speed of the ship and the draft of the ship, as well as
on the depth of the navigational channels and port water area, i.e. ratio (T/H). Additional water mass
coefficients are usually used for calculation, which are presented in Figure 4, when the ship moves in
the longitudinal direction, which corresponds to the navigation of ships in port channels [4,5].
The generation of emissions when a ship navigates port navigation channels and port water
areas depends on the amount of fuel consumed, the power used by the engine(s) and the engine(s)
working time and can be calculated using the methodologies presented in [7, 35].
The Kalman filter [66] and the maximum distribution method [67] were used for the processing
and generalization of the obtained theoretical and experimental results.
The methodology presented in this part allows to determine the optimal speed of the ship in the
shipping channels of the port and the water areas of the port, when the ships is still well controlled
while sailing through it and at the same time consumes the minimum possible fuel.
By using the lowest possible power of the ship's engine(s) and the lowest possible fuel
consumption, the ships produces minimum emissions [62, 64] which is important for the
development of sustainable and green ports.
The main tasks of the developed methodology are based on theoretical models that can help to
find the optimal navigational parameters of ships in port navigation channels and port water areas,
to guarantee navigation safety, to use the safe minimum power of the ship's engine(s) and the possible
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minimum fuel consumption in order to generate minimal quantities of emissions as possible and
minimize the impact on the environment, which is important for the development of sustainable and
green ports. The developed methodology can be applied in practice.
4. Case study of the ships sailing in port channels and port water areas
Klaipeda port [9, 68] (Figure 5) and two types of ships are taken as a case study: PANAMAX
class container ship and POST PANAMAX class bulk cargo ship.
Figure 5. Klaipeda port navigational channels and port waters [9, 68].
PANAMAX class container vessel length is about 294 m, length between perpendiculars about
278 m, width about 32.5 m, draft up to 12.5 m (fully loaded), block coefficient about 0.7, engine power
about 20 MW, maximum speed about 22 knots, minimum speed about 5 knots, container capacity
about 4800 TEU. POST PANAMAX bulk ship length about 235 m, length between perpendiculars
about 210 m, width about 36 m, draft about 13.3 m, deadweight about 78000 tons (full loaded), block
coefficient about 0.82, engine power about 8 MW, maximum speed about 14.5 knots, minimum speed
about 3.5 knots.
For the analysis of the case, the mentioned real ships sailing in the shipping channels of the port
and in the port water area and the calibrated simulator "SimFlex Navigator" [69] were used. The
experimental data of the mentioned real ships were used for the simulator calibration, and later part
of the research was carried out with the help of the mentioned simulator. The obtained simulator
results were additionally compared with the results of real ships sailing in analogous conditions.
Summarized calculation results obtained using the developed methodology presented in Chapter 3
and experimental results obtained on real ships and with the help of a simulator, as well as using the
AIS system for additional comparison [70]. The obtained results were analyzed and the best possible
solutions were sought by using the methodologies presented in [64, 65] and other sources and
adjusting the developed methodology.
The minimum speed of controllable ships in typical harbour depths, depending on the wind
speed and direction, obtained by calculation according to the methodology presented in Chapter 3
and experimentally with real corresponding ships and with the help of a calibrated simulator (the
results presented in Figures 6 and 7 were obtained during experiments on real ships and with the
help of a calibrated simulator).
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Figure 6. The minimum speed at which the PANAMAX container ships can be controlled depends
on the wind speed and the angle of the wind course ( o
a
q) in case of T/H = 0.87.
Figure 7. The minimum speed at which the POST PANAMAX bulk ships can be controlled depends
on the wind speed and the angle of the wind course ( o
a
q) in case of T/H = 0.9.
According to the obtained optimal solutions, the fuel consumption of the ships' main engines
and the resulting emissions were analyzed when the ships sailed from the port entrance to different
port terminals: container and bulk cargo terminals, where the total sailing distances was about 5.0
nautical miles.
First, the minimum relative fuel consumption of the ships (PANAMAX container ship and POST
PANAMAX bulker) was investigated when sailing at great depth (T/H less than 0.2). The study found
that the main engine power of the PANAMAX container ship at minimum typical relative fuel
consumption was about 5 MW and the corresponding ship speed was about 8.4 knots. The main bulk
carrier POST PANAMAX had an engine power of about 2 MW at minimum relative fuel
consumption, corresponding to a ship speed of about 5.8 knots.
Depending on the ratio of the ship's draft to the depth of the navigation channel (T/H) and as it
increases, the resistance of the ship's hull increases. In this way, with increasing T/H ratio and with
minimal typical relative fuel consumption, the speeds of PANAMAX containers and POST
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PANAMAX bulk carriers, calculated according to the methodology presented in Chapter 3 and
verified on real ships and with the help of a calibrated simulator, are presented in Figure 8.
Figure 8. The speed of ships at minimum relative fuel consumption is calculated according to the
methodology presented in Chapter 3 and received on real similar ships and by calibrated simulator.
The possible optimal speed of the investigated vessels in the harbor navigation channel was
investigated, depending on the ratio of the ship's draft to the depth of the channel, as well as the wind
speed and the most unfavorable angle of the wind course (the angle of the wind course is about 90°)
(underestimated current, because the direction of the current coincides with the direction of the
channel). Speed evaluations of PANAMAX containers and POST PANAMAX bulk cargo ships and
other ships with similar parameters were performed in the most unfavorable wind directions, after
estimating the minimum fuel consumption, calculated according to the methodology presented in
Chapter 3 and the results of the evaluation in the SimFlex Navigator simulator [68] and verified by
experiments under the same conditions with real ships of the same type are shown in Figures 9 and
10 as an example.
Figure 9. Minimum maneuverability and minimum relative fuel consumption (Min RFC) speed of a
PANAMAX container ship at various wind speeds and the most unfavorable wind course angle
(about 90°) depending on the draft to depth ratio (T/H) of the vessel. The results are obtained
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according to the methodology presented in Chapter 3 and on real similar ships and a calibrated
simulator with a wind speed of 10 m/s (example).
Figure 10. The minimum maneuverability and minimum relative fuel consumption (Min RFC speed)
speed of a POST PANAMAX bulk ship at various wind speeds and the most unfavorable wind course
angle (about 90°) depending on the ship's draft to depth ratio (T/H). Results received by methodology
presented in section 3, and on real similar ships and by calibrated simulator in case wind velocity 8
m /s (as example).
In this way, the optimal speed of the container ship PANAMAX when sailing to the port of
Klaipeda would be about 8 knots (permitted speed of ships in the port - up to 8 knots), sailing time
about 0.625 hours. At a speed of 8 knots, the main engine of the PANAMAX container ship has a
relative fuel consumption of about 0.15 kg/kWh, and during the test voyage (5 miles), this vessel
consumed about 470 kg of diesel fuel and generated about 1500 kg of 2
CO . The optimal speed of a
bulk cargo POST PANAMAX type ship when sailing to the port of Klaipeda would be about 5.6 knots
(the permitted sailing speed in the port is up to 8 knots), the sailing time is about 0.89 hours. Sailing
at a speed of 5.6 knots, the bulk carrier POST PANAMAX had a relative main engine fuel
consumption of about 0.15 kg/kWh and during the test voyage (5 miles) this vessel consumed about
270 kg of diesel fuel and generated about 860 kg of 2
CO .
When a POST PANAMAX bulk cargo ship enters Klaipeda port at a speed of 8 knots, the sailing
time is about 0.625 hours. At 8 knots, the POST PANAMAX bulk carrier has relative main engine fuel
consumption of about 0.19 kg/kWh, and during the test voyage (5 miles) this vessel used about 325
kg of diesel fuel and generated about 1040 kg of 2
CO . A POST PANAMAX bulk cargo ship in
Klaipeda port consumes about 55 kg less diesel fuel and generates about 180 kg less 2
CO than when
sailing at a speed of 8 knots while sailing the same route at a speed of 5.6 knots. About 300 bulk
carriers of similar size enter the port of Klaipeda per year, therefore, taking into account the arrival
and departure of ships from the port, sailing at the optimal speed (5.6 knots) compared to the
permitted speed (8 knots) would allow to reduce about 33,000 kg of diesel of fuel and generate about
106,000 kg less 2
CO .
The results of theoretical and experimental studies obtained in this way allow them to be applied
in determining the possible optimal speed of ships in port navigation channels and port water areas.
The optimal speed of ships allows to guarantee the safety of navigation in ports, to reduce fuel
consumption and at the same time to reduce the generation of emissions when ships navigate the
port navigation channels and port water areas, which positively influences the development of
sustainable and green ports.
The results of the calculation and experimental research of the case study clearly substantiate
that the optimal sailing speed of the PANAMAX container ship in the port channels and in the port
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water area is about 8 knots, while the optimal sailing speed of the bulk cargo POST PANAMAX type
ship is in the port in the shipping channels and the harbor area there is about 5.6 knots (speed allowed
in the harbor is 8 knots). When sailing at specified speeds under standard sailing conditions, the
tested vessels consume minimal energy (fuel) and generate minimal emissions. At the same time, the
tested vessels do not need to use high engine power for braking when entering the turning basin,
which also reduces energy (fuel) consumption and generates minimal emissions during this
operation.
The results of the experiments on minimum ship controllability speed and minimum fuel
consumption obtained on real ships were used to calculate simulator correction factors (simulator
calibration). With the help of a calibrated simulator, over 20 tests of ships sailing through port
channels at low clearances were performed, which showed that the methodology developed and
presented in the article can be used for scientific research and practical use in planning port channels,
determining optimal conditions for ships sailing in ports and sustainable and green ports
development.
Synthesis of experiments with real ships sailing at minimum controllable speed and minimum
fuel consumption and calibration of the simulator based on real experiments and subsequent
comparison of the obtained results with calculation results using the developed methodology
allowed to assess the reliability of the methodology and the possibility of using the methodology in
other ports and waterways.
Similar partial studies were carried out in Polish and other ports [48, 55], the results of which
are presented in [7, 22, 28, 55] and other works with different types of ships.
The results of the study also revealed that the qualifications of port pilots, ship captains and
tugboat captains are important when maneuvering ships in ports, so their high qualification and
good knowledge of ship controllability can help optimize fuel consumption and minimize emissions
generated by ships.
5. Discussions
The paper discusses a number of measurements of ship movements in navigable harbour
channels, carried out during the case study. Although this number was limited, it is representative of
the research topic. Differences in operator behaviour during manoeuvring operations were observed
and demonstrated that the skill level of port pilots, vessel and tugboat masters varies and is related
to optimal vessel selection speeds. Therefore, it should be noted that the results of the study can be
considered satisfactory and allow answering the first research question, i.e. i.e. whether optimization
ensures optimal speed in port navigation channels and port water areas.
It should be emphasized that the research results were influenced by external conditions that
limited the number of experiments. The interface between real experiments and the use of a calibrated
simulator made it possible to expand the research and the conditions of its performance. At the same
time, it would be appropriate to continue the experiments, taking into account the external conditions
in different seasons, in other ports and compare the results. Based on this, it will be possible to define
more precisely the external conditions under which it is especially important to guarantee the
navigational safety of shipping, taking into account the qualifications of the personnel, in order to be
able to make the right decisions and reduce the power of ship engines when sailing and manoeuvring
ships in ports, to reduce fuel consumption when navigating port navigational channels and port
water areas and minimize the amount of emissions generated by ships entering and leaving ports, as
well should make positive influence on sustainable and green ports development.
Moreover, research results may have managerial implications. Seaports, as well as shipping
companies, may change their procedures and introduce strict conditions of skill verification during
employee hiring and professional work, in pursuit of optimizing the ships speed in port navigational
channels and port waters and as well emissions at seaports. Companies may organize regular
trainings and invest in employees’ education aiming at improving staff qualifications in supporting
decision-making during sailing and manoeuvre operations in ports. These activities may affect the
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development of companies’ navigational safety and environmental policy in order to decrease the
costs of ships’ energy (fuel) consumption, as well as volume of emissions.
The methodology presented in the article could be successfully used to optimize the ships speed
in port navigation channels and port water areas. Port services responsible for navigational safety of
shipping should also be made aware of the minimum controllable ships speeds in various situations
and evaluate it when organizing shipping in the port.
The obtained results of research on the possible minimum speed of movement of ships in the
port, depending on the impact forces and the depth of the navigation channels, using the calculation
method presented in the article, showed the possibility of using this method in port conditions and
reducing fuel consumption and the amount of emissions in the port. The minimization of fuel costs,
using the optimal ship’s speed in the port, which guarantees the safety of navigation, is especially
important in ports located within the boundaries of cities, because it is possible to significantly reduce
the impact on the environment in the port and improve the living conditions of the city residents due
to reduced ship emissions.
At the same time, it is an important scientific contribution of the ongoing research, as a new
methodology has been developed that allows determining the optimal ship speeds in port channels
and port waters with minimal fuel consumption and minimal impact on the environment, when there
is low clearance, which at the same time emphasizes the novelty of these researches and the article.
Detailed studies of the minimum ship handling speed under the influence of external forces and
at shallow depths and a good knowledge of these phenomena can increase the safety of ships sailing
in harbour channels and water areas.
The developed method provides an opportunity to analyse empirical data of real ships obtained
by various modern methods (using high-precision navigation equipment, automatic ship
identification systems, use of calibrated simulators) and can be applied in practice. In addition, the
presented method can be useful for seaports and shipping companies in reducing fuel consumption
and reducing environmental impact as well sustainable and green ports development.
More detailed and complex studies of external factors influencing the optimal manoeuvring of
ships in port channels and water areas, fuel consumption of ships and reduction of generated
emissions, turning of ships in port turning basins, bringing ships to and from port quays, using ship
thrusters and tugs, in the presence of high wind and current velocities, research will be the direction
of our further research. In future studies, we will try to expand the number of measurements and
include more vessels and operators to participate in similar studies.
6. Conclusions
In this way, based on the research conducted and the results presented in this article, the
following conclusions can be drawn:
The developed methodology for calculating the minimum ship-controlled speed at low
clearance allows it to be used in port conditions and at the same time improve navigation safety in
ports.
Matching the minimum controlled ship speed with minimum fuel consumption when sailing in
harbour navigational channels at low clearance allows to reduce not only the ship's fuel consumption,
but also to minimize ship emissions.
Conducted experiments with real ships in order to verify the minimum ship controllability
speeds and fuel consumption allowed to confirm the correctness of the obtained theoretical models.
The developed methodology for the assessment of minimum ship speed, minimum fuel
consumption and minimum emissions from ships can be successfully used for training and research
purposes in assessing the safety and environmental impact elements of port navigation.
Ship operators can successfully use the presented methodology to ensure navigational safety,
reduce fuel consumption in port canals and port waters, and reduce emissions in case low clearances,
what is typical of ports and other waterways.
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The use of modern ships and the optimization of fuel consumption for ships navigating the
port's navigational channels and port waters have a positive impact on the development of
sustainable and green ports.
Author Contributions: This paper was drafted and written by V.P. and all authors worked on the test and
simulation results. D.P. contributed to the query, determination, and calculation of the simulation program. V.P.,
V.S., D.P and MS provided guidance for the overall research ideas and plans. V.P., V.S. and D.P. provided
guidance for the formulation and implementation of test methods. All authors have read and agreed to the
published version of the manuscript..
Funding: This research received no external funding
Acknowledgments: This article is based on the research conducted in Maritime Engineering Department of the
Klaipeda University.
Conflicts of Interest: The authors declare no conflict of interest.
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