107

1 INTRODUCTION

One of the most important aspects in assessing the

safety conditions of the operation of a port terminal is

the verification of mooring plans for ships. According

to [1], the function of the lines and mooring systems is

to keep the vessel moored, in order to allow a cargo

handling operation within tolerable safety limits. In

addition, mooring plans must work with as few lines

as possible, in order to ensure higher efficiency in the

ships entrance and exit operations.

In order to ensure a safe and efficient mooring

system, the tension in mooring lines must not exceed

its minimum breaking load and, at the same time, the

vessel movements shall be minimum as it is possible,

according to the cargo type handled. International

recommendations such as [2] and [3] set out the basic

guidelines to be considered when evaluating mooring

plans.

Especially in regions where the port is subjected to

severe environmental actions, such as waves, currents

or winds of moderate to strong intensity, or in

confined areas where the passage of other vessels

occurs near berths, the moored vessel is subject to

forces that may result in excessive movement. These

movements, in turn, can result in excessive tension on

the mooring lines, which, in extreme cases, can cause

serious accidents in case of line break.

Thus, in places where there are adverse conditions

for the maintenance of ships safely docked in the

Definition of Mooring Plans for Vessels at Port

Terminals Using Physical Models

.C. de Melo Bernardino

University of Sao Paulo, Sao Paulo, Brazil

L.M. Pion, R. Esferra & R. de Oliveira Bezerra

Hydraulic Technological Center Foundation, Sao Paulo, Brazil

ABSTRACT: Physical scale models have a large range of application in studies of hydraulic works. In port

engineering, they can be used to optimize the general layout of terminals, evaluation of protection structures,

simulation of vessel maneuvers and investigation of mooring plans for vessels, among several subjects. Once

physical modeling allows a high accuracy in the waves and currents representation as well as their interaction

with the bottom and the vessels, the studies of mooring systems in coastal and estuarine ports based on

physical modeling tests provide greater reliability in comparison with those grounded on distinct types of

models. To highlight the importance of this kind of application, this article presents the case study of the Ponta

da Madeira Port (PMP), located in the State of Maranhao, Brazil, developed with the support of the 1:170 scale

reduced physical model conceived and calibrated for this area. This study analyzed several alternatives to

improve the availability of the northern berth of the Pier III of PMP, including new mooring strategies and the

construction of a new improvement structure. The results, which concerned on preliminary tests of the mooring

lines tensions, evidenced structural intervention could substantially reduce the risk of mooring lines break,

indicating that further investigations concerning different layouts for the improvement structure are promising

in order to provide an increase of this berth availability.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 13

Number 1

March 2019

DOI: 10.12716/1001.13.01.10

108

berth, the development of studies about mooring

system is essential, considering each critical scenario

for each mooring berth and type of vessel. In these

cases, physical modeling stands out as one of the most

reliable options to perform the analysis of mooring

conditions

Physical models are generally small-scale

representations of any physical system and its

applications in Engineering are widely discussed in

the international literature, in references such as [4],

[5], [6] and [7]. In the case of port studies, hydraulic

physical models, also shortly called scale models, can

be used to represent the entire interest area, including

topography, bathymetry, docking structures, vessels

and also the environmental conditions, such as water

level variations, waves, winds, and so on.

The scale models can be used in several types of

port studies, among which [8] highlights:

 Shelter of waves and / or currents, intervening in

the geometry of piers, breakwaters, jetties, access

channels, maneuvering basins, etc.

 Characteristics of berths, intervening in their

orientation, type of structure, etc.

 Mooring characteristics, intervening in the

arrangement of bollards, or quick release hooks,

arrangement and type of fenders,

recommendations on the Number and type of

lines, as well as pre-tension levels.

This article describes studies based on physical

modeling developed to improve the mooring

condition at a Brazilian Port, the Ponta da Madeira

Port (PMP) located in the northeast of Brazil, in the

Sao Marcos Bay. Considering iron ore exportations,

PMP is the most important Brazilian Port.

The Sao Marcos Bay area is sheltered from wave

action and is enough deep and wide to receive Very

Large Ore Carriers (VLOC). However, this area is

subjected to high water level variation, which can

reach heights of up to 7 m in equinoctial spring tide.

Consequently, the currents inside the bay are very

strong, causing problems for navigation and safe

mooring of vessels.

Thus, a small-scale hydraulic physical model was

built and calibrated within the Hydraulic

Technological Center (CTH), which is the Hydraulic

Laboratory of the University of São Paulo, in order to

develop studies concerning the PMP operations. The

present article discusses one of the case studies

carried out for this port, with support of physical

modeling, which aimed the reduction of the

downtime of the north berth of the Pier III. During

this study case different alternatives, such as new

shelter or berthing structures and different mooring

plans, were analyzed to allow safe mooring in this

berth, even for the most severe tidal current

conditions.

2 MATERIAL AND METHODS

2.1 Study area description

The Sao Marcos Bay, the largest Brazilian bay, is

located in the Northeast of Brazil, in the State of

Maranhao, , bounded to the west by the continent, to

the east by the city of Sao Luis and to the south by the

mouth of the Mearim River.

This bay has great potential for port installation,

because of high depths and wave protection within it.

For this reason, several important Brazilian ports are

grouped in this place, among which stands the Ponta

da Madeira Port (PMP): a private port specialized in

iron ore exportation. Figure 1 illustrates the study site.

This port comprises three main piers, named in the

order of its construction, as Piers I, III and IV (Pier II

is located a little further south and it was not

considered in this study). Figure 2 shows the location

and arrangement of piers PI, PIII and PIV.

Figure 1. Location of the Sao Marcos Bay and the Ponta da

Madeira Port (PMP).

Figure 2. Location of the PMP and Piers I, III and IV, with

emphasis on Pier III, which will be the subject of this article.

Although it is a region with great potential for the

installation of ports, San Marcos Bay presents a

natural condition that imposes great difficulty for the

navigation and mooring ships. Average tidal

amplitude is about 4.5 m, reaching approximately 7.0

m in equinoctial spring tides. This huge variation of

the water levels within the bay results in very high

current speed, which hinder safe maneuvers and

docking during loading or unloading operations.

2.2 Scale Model Description

Concerning the Sao Marcos Bay environmental

dynamics, and considering the PMP is the most

important iron ore export port in Brazil, the CTH was

hired to develop physical modeling studies to support

its port operations. The limits of the three-dimension

physical model built are represented on Nautical

Chart 413 of the Brazilian Navy illustrated in Figure 3.

The main purpose of these studies is to assure the

safety of port operations, considering the goals of

109

improving operating conditions to receive larger

vessels and increase efficiency.

Figure 3. Nautical chart nº 413 and the limits of the physical

model of the Sao Marcos Bay.

The physical model was built on the non-distorted

linear geometric scale of 1: 170, considering the

similarity criteria of Froude, and was reproduced

with fixed bottom. Figure 4 shows an overview of the

model, which has an area of approximately 1,700 m².

Figure 4. General view of the three-dimensional physical

model of the Sao Marcos Bay in CTH-University of Sao

Paulo.

The use of the scale models to represent real

environmental conditions is based on the Similarity

Theory.

The complete similarity between two flows is

obtained when there is equality between all the

relevant dimensionless obtained using Buckingham's

Theorem [4]. In the case of free surface flow, usually

the dimensionless that govern the phenomenon are

the Reynolds Number, the Froude Number and the

Weber Number, detailed as follows:







: Reynolds Number (1)





: Froude Number

(2)









: Weber Number (3)

in which:

U : mean velocity of the flow (m/s)

D : linear dimension (m)



: kinematic viscosity of water (m²/s)

g : gravity acceleration (m/s²)

: depth of the flow (m)



: specific mass of water (kg/m³)



: coefficient of surface tension of the water (N/m)

The Reynolds Number is given by the ratio

between the inertial forces, represented by the

velocity and the viscous forces (kinematic viscosity

coefficient). The Froude Number is the ratio between

velocity and gravitational force. The Weber Number

relates the forces of inertia to the forces of surface

tension.

Mathematically, it is possible to verify that, for two

distinct flows, the equality between all the

dimensionless occurs only if the geometric scale

between both is equal to 1. Of course, for practical

applications in studies of port structures, it is not

possible to build models in real scale (1:1). In other

words, for the practical use of scale models, it is

necessary to apply the principle of incomplete

similarity, in which the equality of the more important

dimensionless for accurate representation of the

phenomenon is prioritized. In the case of free flow,

the equality between the model and prototype (real

environment) Froude Numbers guarantees an

adequate reproduction of the flow conditions, and

allows the determination of important physical

quantities through the tests performed in scale

models. It is important to mention that the incomplete

similarity in modeling implies some scale effects and

limitations during the tests, which need to be

considered according to the objective of the study.

The scale model of Sao Marcos Bay was designed

based on the Froude similarity criteria for free surface

flows. This condition, by itself, establishes the

relations of extrapolation for the prototype of the

several quantities measured in the model.

Establishing equality between the Froude

Numbers of the model (subscript “m”) and the

prototype (subscript “p”) by Equation (2):

gy gy





(4)

Knowing that the geometric scale (



) can be

written as a relation between prototype and model of

any linear quantities (

L ):

Shallow water conditions

110



 (5)

Other fundamental quantities can be written in

relation to this scale factor, such as:



 : velocity scale (6)



 : Volume flow rate scale (7)



 : time scale (8)



 : force scale (9)

2.3 Scale Effects and Calibration of the physical model of

Sao Marcos Bay

The effects due to not represent the viscosity of the

water (represented by the Reynolds Number) in

small-scale models, for example, can be ignored if the

flow in the model is rough turbulent. This can be

achieved by observing a minimum reduction scale for

the physical model (1: λ)

min, which can be obtained by

the Zeghzda criterion [4]. Using the logarithmic

expression for the characterization of turbulent flow

velocity distribution, the minimum scale of the

physical model can be calculated from the expression:

1 126

..2

3,71.

log

Re D















  





















(10)

where:

D : hydraulic diameter



: bottom roughness, which can be estimated by



26.n



 [5]

n : Manning Number.

Thus, in the berthing area of the PMP, in which the

flow velocities are close to 6 knots (approximately 3

m/s), the mean flow depth is about 25 m (the

hydraulic diameter can be approximated by 4 times

this value) and the Manning Number is close to 0.035

(value obtained from calibration in a computational

model presented later in this paper), the minimum

scale calculated by Equation (10) results in: (1 / λ) ≈

1/179. Therefore, the scale adopted for the scale model

of Sao Marcos Bay (1/170) has scale effects due to

viscosity that can be ignored in the berthing area.

In addition to the topographic and bathymetric

characteristics of the region, the vessels are also

reproduced in small scale. For this, based on the

arrangement of lines and the general arrangement of

the real vessel, the hull model and the mooring

elements are conceived according to the geometric

similarity. Furthermore, the vessel’s model is

calibrated for real vessel building data, mainly using

of its gravity center and rotation radius.

The flow calibration process was based on water

level, current speed and direction data, extracted from

a numerical hydrodynamic model conceived for the

same interest area, which is further described in this

paper, at twenty-four homologous points. This model

was calibrated for seven different points within the

interest area, where current speed, direction and

water level data were acquired during a one-year

field survey.

During physical model tests, flow speed and

direction are acquired with a MicroADV (Acoustic

Doppler Velocimeter), and water level is measured

with depth probes, applying the methodology

presented in [9].

2.4 Forces and Displacement Measurement Systems

The parameters controlled and measured during

mooring tests are basically the ship movements and

the forces induced in the mooring lines systems by

these displacements. The tests are performed

considering the elastic stress limits applied in the

mooring lines. For this representation and tension

measurement in the lines, a helicoidal spring is

connected to a displacement sensor. Each line is

positioned on the projection corresponding to a real

mooring element. This system is installed in each set

of lines that support and obey the real geometry,

maintaining the same angle in relation to the vertical

obtained in prototype. The efforts on the mooring

system are acquired by the electromechanical

calibration of this set, which reproduces the lines

characteristics in scale. The Figure 5 illustrates the

forces measurement system.

Figure 5. Forces measurement system in the scale model of

Sao Marcos Bay – CTH – University of Sao Paulo.

The ship displacements on the horizontal plane of

are acquired through a software developed at the

CTH, based on two cameras equidistant from the

instantaneous center of rotation of the boat and two

fixed targets in the same deck, according to Figure 6.

The cameras are able to measure the vessel

movements during the test from its initial position in

three degrees of freedom: Yaw, Surge and Sway.

111

Figure 6. Measurement of vessel movement System by

images.

The fenders are reproduced by steel blades, which

are calibrated from the stiffness curve in addition to

the absorption energy. These elements are fixed to the

homologous places on the berths walls observed in

the prototype, for reproduction of the real mooring

conditions.

3 RESULTS AND DISCUSSION

The North Berth of Pier III of the PMP receives vessels

of the Capesize class of 180,000 DWT. For the higher

tidal amplitudes that occur in the Sao Marcos Bay,

this berth has operational restrictions, which

represents a reduction in its availability throughout

the year. In order to reduce this downtime,

engineering solutions were analyzed in numerical

and physical model tests, looking for increasing this

berth’s availability, considering safety limits and

without causing significant impacts on the sediment

dynamics at the interest area and its adjacencies.

For preliminary tests, a hydrodynamic and

morphologic computational model of the region was

applied. This model was conceived and calibrated on

the MIKE3® platform, developed by DHI (Danish

Hydraulic Institute). The results of these tests allowed

the definition of the most promising alternatives to be

investigated in the physical model at a later stage of

the studies.

The computational grid covers the entire Sao

Marcos Bay, with a grid of more than 30 thousand

cells, which density increases in the vicinity of the

PMP piers. The Figure 7 shows the elements of the

numerical grid. The main problem, which restricts the

operation of the northern berth of Pier III, is the action

of the currents, during the flood tide. In this

condition, the velocities can be very intense near the

north end of this berth, pushing the vessel hull out of

the berth, and forcing mainly the forward breast lines.

The Figure 8 presents an output of the computational

model illustrating the current field in the northern

berth of PIII.

Figure 7. Numerical grid of the three-dimensional

hydrodynamic computational model of Sao Marcos Bay on

the Mike 3® platform.

Figure 8. Currents of the flood tide near Northern Berth of

PIII.

112

Figure 9. Alternatives of shelter wall (highlighted in red color) to decrease the currents action on the vessel in Northern

Berth of PIII.

The study of alternatives to find a solution that

decreases the downtime of the Northern Berth of Pier

III, analyzed the implantation of two types of

structures: a shelter wall at the north end of the Berth;

and a mooring dolphin to the north of the berth.

For the shelter wall, six different layouts (1, 1A, 2,

2A, 3 and 3A) were analyzed in the computational

model, as shown in Figure 9. The alternatives studied

were defined to cause the least possible impact on the

mooring plans of the other berths and on the

sediment dynamics of the area.

The study of alternatives performed preliminary in

the computational model analyzed the variation of

velocities along all the berths and possible changes in

orders of the magnitude of the sediment deposition.

The computational simulations indicated the

layouts 1A and 2A had the best performance

considering the mentioned criteria. Both alternatives

caused a significant decrease of the velocities near the

berthing area in the Northern Berth of Pier III, and in

periods of flood tide, as well as they reduced the

velocities in the other berths of Piers I and III.

However, during periods of ebb tide, especially the

Alternative 2A causes an increase in the current

velocity near Pier I berthing line and the southern

Berth of Pier III. For these conditions, Alternative 1A

presented more similar and favorable results.

In addition, the results of the computational

simulations showed both Alternatives 1A and 2A do

not significantly cause changes in the sediment

distribution of the PMP area.

Based on these results, only the alternatives 1A

and 2A were tested in the scale model of Sao Marcos

Bay for mooring lines tension analysis. These tests

were performed considering vessels docked in in all

berths of the PMP, which represents a critical

condition for this port operation. The Table 1shows

the vessels used in the each PMP berth and Figure 10

illustrates this typical test condition.

Table 1. Class of vessels used in the scale models tests for

evaluation of forces on the mooring lines.

_______________________________________________

Pier Berth Vessel DWT

_______________________________________________

PI --- VLOC 350,000

PIII North Capesize 180,000

PIII South Capesize 180,000

PIV North VLOC 400,000

PIV South VLOC 400,000

_______________________________________________

Figure 10. Picture of the Physical Model of Sao Marcos Bay

with all the berths occupied by a vessel (according to the

Table 1). Highlighted the Northern Berth of PIII (PIIIN).

113

Figure 11. Alternative with an implantation of a mooring dolphin and the mooring plan “P3N9”.

The physical model tests indicated that both

implantations of the shelter walls 1A and 2A lowered

the mooring line tensions at the vessel’s bow, when it

is moored at the northern berth of Pier III. However,

an increase in mooring line tensions was detected at

this ship’s stern. An increase in mooring line tensions

was also detected at forward breast of the ship

moored in the southern Berth of the same pier for the

two alternatives.

Regarding these results, another structural

alternative was investigated in the scale model. It was

an additional mooring dolphin, near the northern end

of Pier III. Two positioning alternatives were studied

for this dolphin, as well as five different mooring

plans, four of them with a more distant dolphin and

one with a dolphin closer. The best results were

obtained for the mooring plane called "P3N9", with

the dolphin closest to Pier III. This alternative is

illustrated in Figure 11.

The physical model tests showed that the closest

dolphin alternative allowed the implantation of a

mooring plan which assures docking safety for

practically all tidal amplitudes that occur in Sao

Marcos Bay. P3N9 plan (Figure 11) enabled an

increase of approximately 60% on the availability of

northern berth of Pier III, when compared to the

original condition

Moreover, since the dolphin structure is relatively

slender, it practically does not interfere in the local

current field and, thereafter, does not affect the

mooring conditions in the other PMP berths nor

causes any significant impact on sediment deposition

at the PMP and its adjacencies.

4 CONCLUSIONS

Small-scale hydraulic physical models are a powerful

tool for engineering studies. In the case of the

evaluation of the safety of mooring conditions at

ports, the experience of the work developed by CTH

has shown that the results obtained in these studies

accurately represent the reality. Several measures of

tensions on the mooring lines of real ships have been

compared over the years with the physical model

tests results, allowing confirmation of the

effectiveness of this tool.

In the case of the studies developed for the

Northern Berth of the Pier III of the PMP, presented in

this article, preliminary studies of alternatives in

computational modeling allowed to define the two

better layouts of a shelter wall structure, which

reduced the current speed near this berth and with

minimum interference on sediment transport. ,.

However, when these alternatives were tested in the

physical model, both proved to be inefficient in

decreasing the downtime of this berth, as well as their

implementation caused an increase on the mooring

line tensions for vessels docked at adjacent berths

Further investigations of alternatives in the

physical model concluded that the most promising

solution is the implantation of a dolphin near the

north end of Pier III. This solution allowed the use of

a new morring plan (P3N9), with a reinforcement of

the forward breast lines, that was able to keep the

vessel moored in safety for almost all environmental

conditions. Considering the implementation of this

alternative, the downtime of the Northern Berth of the

PIII was reduced significantly.

In addition, the alternative of the dolphin had no

effects on the mooring conditions of ships in other

PMP berths, as well as this solution showed no

significant change in the complex and intense

sediment dynamics of the region.

From the study developed for the Northern Berth

of PIII, future studies in the physical model will allow

the optimization of the mooring plans for this berth,

using the new structure of the dolphin and aiming to

suppress any operational restriction.

REFERENCES

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Blücher, 2014. (In Portuguese)

[2] Oil Companies International Marine Forum “Mooring

equipment guidelines”3rd. London, 2013.

[3] PIANC – Permanent International Association of

Navigation Congresses – “Report of Working Group no.

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[4] Novak, P. & Cabelka, J., Models in hydraulic

engineering: physical principles and design applications,

Boston, Pitman, 1981.

[5] Kobus, H., Hydraulics modeling. Bonn, Germany,

DVWK/IAHR, 1981.

[6] Hughes, S.A., Physical models and laboratory

techniques in Coastal Engineering. Advanced Series on

Ocean Engineering – Volume 7. USA: World Scientific

Publishing, 2005.

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114

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