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1 INTRODUCTION
Safetyofportmanoeuvresoflargeself‐manoeuvring
vesselsinconfinedareasofportdocksisrelatedtothe
availablesteeringforcesgeneratedonthehull.
The powerful propulsion and steering devices
produce high energy thrust streams which are
beneficialforshiphandlingbutatthesametime
can
causeseabedscouringanddamageofhydrotechnical
constructions (Blaaauw et al., 1978; Blokland et al.,
1996)).Theassumedloadsfromvesselsareincluded
in requirements of civil engineering codes (BAW
Code, 2010), guidelines (PIANC, 2015;
Reccomendations of the Committee for Waterfront
StructuresHarboursandWaterwaysEAU,2012,2015)
and
modern safety based approach to design taking
into account operation of the vessel and structure
(Gerigk,2015a;Sntoseta.,2015;Taraszkiewiczet.al,
2015).
Theproblemofshipinducedstrongwatercurrents
is the most important in shallow water conditions
(Skupień et al., 2014; Jachowski, 2008) and strong
weather
conditionsclosetothelimitsofportweather
window.
To prevent the scouring and damage of seabed
protection systems port authorities limit the use of
powerof main propulsion units up to 25%‐40%of
themaximum power. In the operationalpractice the
limitsaremainlyrelatedto berthing and
unberthing
operationsattheselectedquaywalls.
The power of bow thrusters of self‐manoeuvring
vesselsinmostcasesisnotlimitedintheoperational
guidelines for port constructions. They have smaller
impactthanmainpropellershowevertheycanhavea
destructiveinfluence.InAntwerpandRotterdamthe
allowabledesignva lues
areassumedlessthan100%
ofmaximumavailable.
Thedesignandoperationalrequirementforferries
and ro‐ro vessels is the ability of crabbing under
lateralwind of7B.Thewidelyusedindustrypractice
istoinstallbowandsternthrusterswithpowerof0.5
– 0.96 kW
per square meter of the windage area.
Therefore the power of the most widely used bow
thrusters is usually in the range of 800 kW to 1500
kW. They are installed in different combinations of
twoormoredevices,veryoftenastwinbowthrusters
ofthesamepoweranddimensions.
Innovative Project of Propellers and Thrusters Jet
Loads during Ship Berthing Monitoring System
T.Abramowicz‐Gerigk&Z.Burciu
GdyniaMaritimeUniversity,Gdynia,Poland
Ł.Hapke
EnamorLtd.Gdynia,Poland
ABSTRACT:Thegrowingnumberoflargehighpoweredvesselsoperatedinshallowwaterportsisthereason
thatportauthoritiesandterminaloperatorsareinterestedinonlinemonitoring ofloadsgeneratedbyvessels
duringmanoeuversclose tohydrotechnical constructions.Thetestversionofthe loadsmeasurementsystem
basedonthemobilelaboratoryandcommercialversionofmonitoringsystembasedonthecloudtechnology
arepresentedinthepaper.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 4
December 2019
DOI:10.12716/1001.13.04.20
862
Thelargecontainershipswhichnormallyusetug
boats assistance in narrow docks in many situations
support the manoeuvres using their own bow
thrustersandpropellers.VLCSandULCS(verylarge
andultralargecontainerships) with capacity 8000‐
21000TEU (twenty‐foot equivalent unit) with 300to
400m
lengthoverallareequippedwithseveralunits
of2000kW‐3500kW.
The power of auxiliary steering devices is
growing.Thelargestbow thrustermadefor acruise
vesselhasthepowerof5500kW(Wartsila,2016).The
highestvelocitiesofbowthrusterjetsareintherange
of4‐
5m/s.
The violation of permissible jet velocity limits
results in the emergence of destructive loads. Their
severitydependsonthejetvelocitiesandtimeofthe
impact.Theextentofdamageisrelatedtothetypeof
seabedprotection(Lametal.,2011;Nakamuraetal.,
2011).
The most susceptible
to damage are the systems
ensuring a soft bottom effect, made of geotextile
mattresses–geotextilebagsfilledwithsandandtied
witheachotherontheiredgeswithropes.Evenafter
asingleviolationoflimitsthisconstructionshouldbe
inspected because the next violation of the allowed
limits
isusuallyfollowedbythedestructionofmuch
bigger area of the seabed protection. The immediate
repairofafewdamagedelementsdecreasesthetotal
maintenancecosts.
The periodical inspections are carried out by 3D
imagingandscanning,experienceddivers orspecially
designed AUV (autonomous underwater vehicle)
(Gerigk,2015b).The
usualtimebetweenconsecutive
inspectionsofseabedprotectionsissixmonthstoone
yearthereforethemaingoaloftheprojectpresented
inthepaperisto solvetheexisted problemofloads
monitoring in real time and warning the personnel
responsibleforberthoperationabouttheexceedance
ofpermissible
loads.
2 INDIRECTMETHODOFMEASUREMENTOF
THRUSTSTREAMSVELOCITIESOVERTHE
SEABED
The maximum velocity over the seabed can be
calculated using German or Dutch method (PIANC
2015). These empirical methods are developed both
formainpropellersandthrusters.
In case of bow thruster induced loads the
empiricalformula(1)
forthemaximumvelocityover
theseabedinfrontofthequaywallrecommendedby
Germanmethodisasfollows:
1.0
max-seabed 0
/1.9
p
L
UU
D





 (1)
where:U
0–istheeffluxvelocityatthebowthruster
outletopening,
‐isthecorrectionfactorofavalue
between0and1forvaluesL/Dpintherangebetween
3and8,anditisdependentontheratioofdistanceL
[m](distancebetweenthethrusteropeningandwall
surface) to the bow thruster propeller diameter Dp
andverticaldistance
z[m]betweenthepropelleraxis
and seabed surface, in other cases
should be
assumedas1(Fig.1)(PIANC,2015).
The maximum flow velocity over the seabed
calculatedaccordingtotheDutchmethodisgivenin
theformofequation(2):
1.0
max-seabed 0
/2.8
p
zL
UU
D




(2)
BothGermanandDutchmethodsarethecomplete
designprocedures.Theformulas(1)and(2)shouldbe
usedrespectivelytothechosenmethod.Bothcangive
almost the same results for sea‐going vessels when
bowthrustersaresituatedaboutashipbreadthfrom
thequaywall.
Inthe
caseoffullbodiedbox‐shapedhullformsin
which the bow thruster tunnel outlets are situated
close to the quay wall the velocities calculated by
German method are about twice bigger than
calculatedbyDutchmethod.
The most widely used formula to calculate the
effluxvelocityispresentedinequation
(3).
1
3
0
2
1.15
d
wBT
P
U
D




 (3)
where:P
d–isthebowthrustergeneratedpower[W],
ρ
w‐is the water density [kg/m3], DBT‐is the bow
thrusterpropellerdiameter[m].
Thecalculationsallowdeterminingthemaximum
seabedvelocitiesandcanbeusedasbasicinformation
whendecisionsofnecessarymonitoringaremade.
Thestraightmeasurementofloadsonthesurface
of a bottom protection cannot be done due to the
possibledamageof
measuringinstruments.
The idea of indirect method of measurement in
case of thrusters is based on the previous
investigationspresentedbyRömisch(1975).
The kinetic energy of the bow thruster jet is
converted into pressure on the quay wall (figure 1).
The conversion of the kinetic energy of a thrust
stream
into the pressure takes place over 0.3 L
distance from the wall surface. The maximum
stagnation pressure on the wall is in front of bow
thrusteroutletopening wherethejetvelocityisequal
tozero.
Figure1.Bowthrusterjetinfluenceonaverticaltightwall
andseabed‐pressurezoneandseabedzone.
Pressure
Zone
Seabedzone
BT
L
z
863
The change of direction of the flow on the quay
wall results with the free surface deformation and
flowformationovertheseabed.Thedecreaseofflow
velocityduetothechangeofflowdirectionalongthe
wall to the seabed can be assumed as negligible
(Römisch,1975).Thevelocity
overtheseabedisequal
to the velocity on the quay wall therefore the
measurement of total pressure va lues on the quay
wall and calculation of related velocities allows for
thepredictionofvelocitiesintheseabedzone.
The prediction of flow velocities over the seabed
generated by propellers is
also based on the
measurementsofdynamicpressureontheberthwall.
Inthiscasetherelationshipbetweenpressureonthe
quaywallandthruststreamvelocityovertheseabed
isobtainedfromCFDsimulation.
The relationship between the dynamic pressure
valuesandflowvelocitycanbeexpressedbyformula
(3)
givingtheresultsclosetoBernoulliequationwith
the percentage error less than 5% (Abramowicz‐
Gerigketal.,2018).
2
471.2 8.8pvv
 (3)
where:p[Pa]–isthedynamicpressure,v[m/s]isthe
flowvelocity.
The indirect method of measurements of bow
thrusters wash over the seabed before it is
implemented in the target online monitoring system
hasbeentestedusingthemeasuringsystemoperated
from the mobile laboratory in
the van car
(Abramowicz‐Gerigketal.,2014;2018).
TheresultsofCFDmodellingandmeasurements
allow determining the proper parameters of the
system,numberand location of sensorsonthequay
wall.
3 ONLINEMONITORINGOFTHRUSTSTREAMS
VELOCITIESOVERTHESEABEDNEARA
QUAYWALL
The idea of
the online monitoring system of thrust
streams velocities over the seabed is presented in
figure2:
Figure2.Onlinemonitoringofthruststreamsvelocitiesover
theseabed.
Thedataarecollectedfromthesensorspositioned
onthequaywallandresultsoftheinitialcalculations
aresentovertheinternet,usingthemodemconnected
tothemainunit,tothe“cloud”,whichisacollection
ofservices(softwareandhardware).
Thenthedataisfurtherlyprocessedwithusage
of
connected resources. It may consist of multiple
physical servers, additional processors or other
hardware parts. This allows scaling the resources
depending on the number of installations or the
amountofthedatatoprocess.
The target monitoring system should be tailor
made.Thebasicdesignassumptionsarethetype
ofa
quay wall construction and expected position of
maximum loads generated by propellers and
thrustersduringoperationsperformedbyvessels.
The example of the measuring module of the
system designed for the ferry terminal in Port of
Gdynia for propellers loads monitoring is presented
infigure3.
Figure3. Position of pressure sensors on the quay wall in
ferryterminalinPortofGdynia.
The example in figure 3 presents the installation
ontheLarssensheetpilingtypequaywalldedicated
to measurements of propeller thrust streams in the
exposedareaneartheterminalramp.
4 DATACOLLECTIONANDANALYSIS
The process of data collection and analysis is
presentedinfigure4.
Figure4.Processofdatacollectionandanalysis.
Data
acquisition
Datasaving
Difference with
referencevalue
Valuetohigh
Alarm Setnewreference
Senddatatoserver
Furtheranalysis
864
Themainelementsofthesystemarepiezoresistive
pressure sensors, providing basic data for further
processing.
The analogue data collected as a total value of
pressureactingonthesensormembraneisconverted
to a digital form with usage of the analog‐to‐digital
converter. Information in this form can
be further
processed and compared with the mathematical
model.
The results are stored in local database and sent
withtheGSMmodemtomainserver.Thenthedata
can be shown to the user with help of the internet
applicationandHTTPprotocol.
The data received from the meas uring system
is
stored on a hard drive or multiple drives, which
increasessafetyofthedata.
Whentheconnectedresources(RAM,CPU,Hard
drives) are not enough powerful, more processing
power can be added to the system with minimal
downtime.
The “cloud” solution simplifies further
development of supplementary elements – data
presentation
onawebsitethroughscalingthenumber
of virtual servers or allowing the access to the raw
dataforaspecificuser.
It is also possible to run servers in multiple
physicallocationstominimalizethetimetheuserhas
towaittoviewthedata.The“cloud”solutionallows
decentralizingthestorageandprocessingmodulesto
minimalizetheinfluenceofonetoanother.
Thereferencepressurevalueforthesystemshould
be checked at least every 5 minutes, taking the
measurements and comparing it with the maximum
limitandpreviousreferencemeasurement.
Ifthemeasuredvalueislower,itbecomes
thenew
reference. If it is higher the alarm is set on and the
referencevalueisnotchanged.
Comparing the difference between measurement
and the reference the damage of the quay will be
detectedifthelimitisexceededfortheassumedtime
(e.g.2seconds)anditcan
beassumedasanaverage
valueofthemeasurement.
The system takes a measurement with 5 Hz
frequency.
Themeasurementdataconsistsof:
pressurevalue,
difference between taken pressure and the
referencepressurevalue,
stateofthealarm.
Anelectronicdiagramofthemeasuringsystemis
presentedinfigure5.
The measurement and reference value is saved
withapropertimestamp.
The system should send the data to ma in server
usingthedirectcontactwithdatabaseorFTP.
Figure5.Electronicdiagramofthemeasuringsystem.
The local data should be stored for the assumed
time e.g. 7 days. 5 measurements x 60 seconds x 60
minutesx24hoursx7daysis3024000recordings.For
24sensorsand4bytesforsingleprecisionnumberit
gives 290304000 bytes, ~280 MB for the
measurements.
The measurement
and reference value is saved
withapropertimestamp.
The system should send the data to ma in server
usingthedirectcontactwithdatabaseorFTP.
The local data should be stored for the assumed
time e.g. 7 days. 5 measurements x 60 seconds x 60
minutesx24hours
x7daysis3024000recordings.For
24sensorsand4bytesforsingleprecisionnumberit
gives 290304000 bytes, ~280 MB for the
measurements.
The data that was sent to server can be used in
further analysis – for example to determine how
manytimesthealarmisseton
inselectedtimerange,
thefrequencyofthemeasurementsbeingtoohighor
thetimeofthedayinwhichmostalarmsareseton.
5 CONCLUSIONS
The presented system for monitoring loads induced
byshipsontheseabedclosetothequaywallduring
berthing and unberthing manoeuvres is
the solution
of decreasing maintenance costs of terminals. It was
initially dedicated to ferry terminals however the
open system architecture allows to adapt it to
differentberths, shiptypesand special requirements
ofportauthorities.Thefirstconclusionsfromthereal
time monitoring carried out within the project are
expectedin
July2019.
865
ACKNOWLEDGEMENT
ThisworkwassupportedbytheprojectRPPM.01.01.01‐22‐
0068/16‐00, “Development of a prototype of a system for
monitoring the loads on berths and bed protection in the
areaofshipberthingalongwiththeimplementationofthe
finalproductonthemarketbyEnamorLtd.companyfrom
Gdynia”within
“SmartSpecialisationsofPomeraniaRegion
– offshore technology, ports and logistics” European
program.
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