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44 PRÁCTICOS DE PUERTOPRÁCTICOS DE PUERTO

SUMMARY

Traditionally, ports have operatedunder fixed rules which govern theminimum under keel clearance (UKC)to permit safe transit along portapproach channels. To ensure safety,these fixed UKC rules are determinedby requirements under extremeswells and negative tidal residuals.These rules have been in existence formany years and are often believed tobe fool proof as in most cases theyhave an unblemished safety recordbut they can fail1, often withdisastrous consequences.

Technology is now available toeffectively mitigate the risk ofgrounding. These systems, modelvessels dynamically in real time toaccurately calculate the underkeelclearance; this ensures that a vesselcannot transit unless it is safe to doso. But there are additional produc-tivity gains in using such systems. Thefixed rules are designed to cover theworst possible conditions, so undermost environmental conditions avessel can usually sail with increaseddraught and/or tidal windows.

This technology is used opera-tionally in the Dynamic Under-KeelClearance System (DUKC®) developedby OMC International. It is a real timeunder-keel clearance (UKC) systemused by ports and shallow waterwaysto maximise port productivity andsafety. The DUKC® considers all fac-tors that affect the UKC of a vesseltransiting a channel to determine theminimum safe UKC requirements.DUKC® seamlessly interfaces proba-bilistic UKC planning (maximumdraught & tidal windows) up to 12months in advance with short termtransit planning utilising real timeenvironmental and vessel specific in-formation and also with UKCmonitoring throughout the transit todeep water. With a track record of 19years and more than 90,000 vesseltransits globally without incident,

DUKC® has a strong history as anoperational tool.

The latest version, DUKC® Series 5,integrates proven core calculation en-gines with a web interface thusallowing easy accessibility to the sys-tem for approved users world-wide.DUKC® users are able to successfullyexecute under keel clearance relatedtasks via the web rather than thetraditional desktop-based user inter-face. The web interface has gainedacceptance by pilots as it allows on-board calculations through a laptopor tablet, such as an iPad.

This paper outlines the differencesbetween static and dynamic systems.It discusses the important featuresof a dynamic system and how adynamic system improves the deci-sion making processes both ashoreand on-board.

1 INTRODUCTION

The majority of ports in the worlduse static rules to determine the safeunderkeel clearance of a vessel.These static rules often use the vesselsdraught as the baseline to determinethe underkeel clearance; however itis contended that this method can beerroneous as they are based on theassumption that this clearance issufficient regardless of the prevailingenvironmental conditions.

In practise, the actual safetyclearance is determined by the condi-tions on the day, and under static rulesthe clearance for a vessel varies forevery transit. For most of the time thestatic rules will be conservative, butevidence shows that up to five percentof transits are marginal, even unsafe2.

By contrast, a dynamic under keelclearance system (DUKC®)3 utilisesreal time under-keel clearances inports and shallow waterways tomaximise channel safety and alsoproductivity. The DUKC® considersall factors that affect the UKC of avessel transiting a channel to deter-

mine the minimum safe UKC re-quirements. The system does notuse the vessels draught as the base-line, but a pre-determined safetylimit which must not be breached;added to this limit are the vessel’sdynamic movements which aremodelled using the predicted envi-ronmental conditions and this givesthe minimum water level that is re-quired to ensure safety at all timesthroughout a planned transit.

The methodology behind dynamicunderkeel clearance has been inter-nationally recognised, and theimproved certainty and informationthat dynamic systems can deliverhas seen regulatory bodies, i.e. IALAand PIANC4, regarding such systemsas an essential Aid to Navigation(AToN) and these bodies aredeveloping standards for dynamicunderkeel clearance systems.

Melbourne-based OMC Interna-tional (OMC) continues to be the onlyspecialist maritime firm in the worldwhose core focus is providingproven technology for determiningand managing real-time UKC indepth-restricted waterways, typicallyapproach channels to ports. With atrack record of 19 years and morethan 90,000 vessel transits globallywithout incident, OMC’s DUKC® hasa strong history as an operationaltool and safety has always had theupmost importance. Increasing in-ternational recognition is beinggiven to the significant benefitswhich dynamic determination of un-derkeel clearance provides as a riskmitigation tool and many ports havebecome increasingly interested ininstalling DUKC® for safety and riskmanagement purposes. However,DUKC® systems have also beenwidely recognised for the enormouseconomic benefits provided towaterway owners and users by re-ducing the inefficiencies inherent inthe static rules when the environ-mental conditions allow.

OMC’s knowledge of hydrody-

Advances in Under Keel Clearance Risk Management

Capt. JONATHON PEARCE OMC International

SUMMARY

1- INTRODUCTION

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PRÁCTICOS DE PUERTO PRÁCTICOS DE PUERTO 55

namics, ship dynamics and experi-ence in system delivery provides aproven model of UKC management.DUKC® offers a paradigm change inthis critical area of maritime safety.International bodies have identifiedDUKC® as a core e-Navigationconcept, which is available and op-erational today.

2 STATIC RULES

Traditionally, ports have operatedunder static rules which governthe minimum under keel clearance(UKC) to permit safe transit alongport approach channels. Thesestatic rules were devised whenvessels were smaller, their speedslower, ship/shore communicationspoor and technology generallyunavailable to determine ship mo-tions accurately. Therefore, thereneeded to be a simple method of cal-culating a safe underkeel clearance,and the accepted practise, was/is tocalculate the underkeel clearance asa proportion of the vessels draught.Whilst any ratio could be used, mostports use ten percent unless condi-tions dictated otherwise. PIANC5

guidelines reference this ratio, but itis often forgotten that this is aminimum suggested safety clearanceand is for calm waters only, and thattwenty, even fifty, percent may bebetter, especially for ports that aresubjected to wave motions.

The static rule tries to capture allanticipated factors6 in a singleallowance. Essentially the only con-trollable factors is the tide height(and therefore transit time) andspeed (which determines theamount of squat). Where there isdeep water, or little or no wave mo-tions this may be suitable, butwhere depths are critical, and con-ditions more variable, there may betimes when the allowance is mar-ginal. It could be suggested that the“static rule” approach is a “top-down” approach, where theclearance is determined from thedraught; from this each of thefactors are removed leaving the netunderkeel clearance.

Some ports do try to assess someof the factors, and this could beviewed as an advanced static rule.But whilst some of these factors canbe pre-calculated, predicted waveresponse (in real time) is impossibleto calculate without significant pro-cessing power and access toenvironmental data; so in practicalterms wave motions are undeter-minable once a transit commences.To address this issue, some portsapply a pre-determined roll/pitchangle to give the ship-handler an in-dication of loss of underkeelclearance due to wave motion7.

Speed is an absolutely criticalelement in maintaining safe UKC.Evidence has shown that pilots do

not always maintain vessel speedwithin the planned limits. If thetransit is too fast, the ship willsquat8 and heel in excess of the pre-dicted amounts: both effects areapproximately proportional to thesquare of the speed; if too slow theship will not reach way points at re-quired times and, in tidalwaterways, may therefore “lose”more water than predicted. Onceunderway these elements can bedifficult to assess and can often beoverlooked. Most ports will use asingle squat formula, but there aremany formulae in existence; themost appropriate formula will de-pend on the bathymetry, channeldesign and the type of vessel. Oftena ship-handler will calculate thesquat for a single critical point, butin practise the vessels squat is con-tinually changing throughout theentire length of the transit.

The biggest drawback with staticrules is that they are whollydependent on the environmental con-ditions. If they are too optimisticsafety could be jeopardised; tooconservative and they become uneco-nomic; so they are blunt compromise,and for safety reasons will often bederived for the worst case scenario.The actual net clearance is propor-tional to the environmental andtransit conditions, but at the sametime unresponsive to change; thismeans a port cannot maximise effi-

2.- STATIC RULES



ciency when conditions allow. Moreworryingly, a port will not be awarewhen conditions are actually unsafe9,because when static rules are used,the level of risk is variable and the netunderkeel clearance on any particulartransit is unknown.

By contrast, dynamic underkeelclearances are determined based onthe actual vessel and its stability pa-rameters, real-time met-oceanconditions (wave height, period anddirection, water levels, currents, tidalplane, wind), vessel transit speed andwaterway configuration, includingdetailed bathymetry, at the time ofsailing. Wave spectra, ship speed andwater depths vary along the transitand the effect of these variations iscomputed by the numerical ship mo-tion model used in each DUKC®

system. In addition, wave spectra andtidal residuals will change over time,and these effects are accounted forin each system. With respect tosquat, individual ships and the per-tinent characteristics of thecomplete approach channel aremodelled in each dynamic system,using the most appropriate squatformula, and include the effect oftemporal and spatial variation oftidal currents during the transit.

Dynamic systems can be viewedas a “bottom up” approach. The sys-tem has, at its core, a minimumlimit10 that must not be breached.Each of the computed factors is thenadded until the minimum tide heightis found that ensures a safe transit.Thus when the conditions arefavourable vessels may have greatertidal windows and/or can sail witha deeper draught; but when condi-tions are not then tidal windows arereduced, and may even be closed, ora vessel may be able to proceed butwith a lighter draught.

The system is also predictive, so ifa pilot wishes to adapt his transitplan (especially the transit legspeeds), or if there is an unforeseenevent (e.g. a berth delay), or there isa change in the environmental con-ditions the system will automaticallyupdate the safe transit windows

OMC’s Dynamic UnderkeelClearance system DUKC® is today amature product. The day-to-dayoperation11 of DUKC®, in preferenceto static rules for UKC, has moved thesystem from academic theory into abest practice in the real world.Integration of the sophisticated nu-merical calculations (the “engine”)with real time environmental data(wave, current and tide) ensures in-tegrity and quality at the criticalinterface between the UKCM systemand the dynamic data.

The accuracy of the numericalmodels used in the DUKC® Systemhas been validated by undertakingmore than 300 ship transitsworld-wide to obtain full-scalemeasurements of vessel speed, trackand vertical displacements. Thesevalidation tests have been undertak-en for a wide variety of channelwidths, configurations and lengths,vessel types, sizes and stability con-ditions, vessel speeds, waveconditions, tidal regimes and currentspeeds. This modelling guaranteesthe accuracy and applicability of themodels within the DUKC® system;each installation uses customised nu-merical models to calculate the UKCrequirements of the particular shipsailing in the particular waterway inthe environmental conditions at theparticular time.

The system has also beenrigorously and independently testedby specialist risk managementconsultants to ensure that it satisfiesinternationally-accepted levels ofrisk for safely managing the UKC ofvessel transits12.

The DUKC® product suite iscontinually being adapted inresponse to customer feedback andavailability of new software technolo-gies since the first installation (DUKC®

Desktop) in 1993. New applicationsdeveloped and deployed include theintegration of the technology onto

3 DYNAMIC UNDERKEELCLEARANCE SYSTEMS (DUKC®)



laptops (or smaller devices) carriedby pilots and into VTS Centresenabling vessel speed and predictedunder keel clearance ahead to bemonitored on board and ashore.

OMC International DUKC Series 5product suite, integrates the provencore calculation engines into a webinterface. DUKC® users are able tosuccessfully execute under-keelclearance related tasks via the webrather than the traditional desktop-based user interface.

The DUKC® Series 5 software con-sists of several modules integratedbehind a single web portal. Eachmodule is self-contained, developedand tested under ISO standards,and proven in the unforgivingworld of maritime operations. Themodules can be arranged and con-figured to help manage underkeelclearance related problems rangingfrom long-term voyage planning toreal-time onboard pilotage applica-tions and to the monitoring ofnumerous vessels in real-timewithin a VTS environment.

At the heart of the DUKC® Series 5software suite is a pair of critical en-gines: An Environmental ForecastEngine and a UKC Calculation En-gine. Each engine consists of tested

and proven sub-components. Builton top of the core engines areservices which provide DUKC® appli-cations with both web and non-webaccess to the underlying engines.

Custom web site configurations arebuilt on top of the DUKC® Series 5 webinterface template to matchcustomer’s required look and feel.Custom interfaces between the DUKC®

Series 5 modules and the variousmet-ocean sources, ship informationsystems and VTS users are configured(or developed where necessary) byOMC for the UKCM system.

Networks of external data sourcessuch as met-ocean sensors, AIS datastreams and GPS positions areprovided to the DUKC® system as re-quired. All DUKC® outputs, diagnosticsand statistics can be logged, queriedor distributed in real-time to users.

From the full collection of DUKC®

Series 5 modules, numerous WebServices can be configured to pro-vide a UKC management system forany waterway.

Engines

The Calculation Engine and itssubcomponents manage everythingfrom complex vessel motion calcula-tions to the logic of transit planning.Its purpose is to compute and solveunderkeel clearance questions.

The Met-Ocean Engine is at thecentre of all met-ocean inputs to the

underkeel clearance calculations.Its three primary functions are:• Quality Assure and Filter: toquality assure and filter allmet-ocean inputs • Data assimilation and prediction:to integrate all available met-ocean measured and predicteddata, ranging from astronomical pre-dictions to real-time sensormeasurements to third-party (inc. na-tional weather service) forecasts, andto produce short term, medium termand long-term met-ocean forecasts.• Spatial Transformation: to predictmet-ocean conditions in betweenand beyond sensor positions. Forexample, the engine computes tidalheights and streams between tidegauges and current meters.

Web Services

1. Voyage planning serviceThe long-range (>24 hours) under-

keel clearance planning componentuses met-ocean forecasts andclimate statistics to estimate whatthe short-term (0-24 hrs.) sailingadvice of the DUKC® will be at somefuture date.

The Voyage Planning Service cal-culates the probability of waves andtides from astronomical tide fore-casts and historical wave and tidestatistics, and uses these to calculatethe most likely tidal window ormaximum draught for a vessel. The

4. - DUKC SERIES 5 - PRODUCTOVERVIEW

ENGINES

WEB SERVICES

Sample output from a met ocean service



level of probability is set to ensurethat the vessel can transit but a usercan decide on a greater ‘risk profile’which would allow a greaterdraught but with the risk of missinga tide. This allows a scheduler tospecify the level of certainty for theship to transit without delay.

2. Met-ocean serviceAllows interactions with the met-

ocean engine described above andhandles all requests related tomet-ocean data. OMC has unifiedmet-ocean data displays available

which are able to display met-oceanmeasurements, forecasts and pre-dictions from many differentsources within a single view.

3. Vessel serviceThe vessel service allows

interaction with a comprehensivelist of recognised vessels, and theirparticulars; this is used as theauthoritative source of vessel infor-mation within the system. Thevessel service can be linked up toexternal vessel data sources suchas port information systems.

4. Transit planning serviceThe transit planning service

manages real-time to short-term pre-dictions of under-keel clearance,which are automatically updatedfrom latest met-ocean observations.The Transit Planning Service is usedto plan vessel transits (including pro-viding speed control functionality inthe planning) through the specifiedwaterway using the latest met-oceanobservations and accurate vessel loadstate information and AIS positions.

This service is the core module for

Sample output from Transit Planning Service

Sample output of speed/tidal gates for each key control point from the Transit Planning Service



safe passage planning and allowsaccurate pre-planning, monitoringand contingency planning of atransit. Access to this service ispossible in real-time or there is thecapability of producing comprehen-sive hard-copy passage plans for thepilot to take onboard.

5. Optimiser Planning serviceThe optimiser planning serviceallows the optimisation of multiplevessel departures on a single tidewhilst considering constraintssuch as tug availability, currentrestrictions and booking priorities.

6. Operations - Transit MonitoringService Shore-based

The transit monitoring service au-tomatically tracks and monitors theunder-keel clearance of 'active'transit plans. Users who have beenassigned permissions to accessmonitoring functionality can trackthe under-keel clearance of one ormore vessels simultaneously.

The under-keel clearance infor-mation is updated continuouslybased using the latest met-ocean ob-

servations, vessel load state infor-mation and AIS positions. Trackingof vessels occurs automatically oncea transit plan has been issued ('ac-tivated'). The Transit MonitorService includes a monitoring chartthat gives operators a geographicview of the UKC status of all vesselsbeing tracked.

7. Operations - Transit MonitoringService On-board

OMC on-board solution providesUKC related information displayedwithin a charting package environ-ment as overlay on top of a chart.This allows UKC information to bedisplayed more intuitively to marinepilots and allows horizontal naviga-tion aspects to be included in theassessment of under-keel clearance.

The chart overlay display of un-der-keel clearance informationallows pilots to make on the fly nav-igation decisions from an under-keelclearance perspective. For example:

• Decisions about safe passing areas• Assessment of the impact of

speed increases on the safetravelling corridor• Assessment of local shoals on thesafe travelling corridor (particularlyimportant where high spots remainafter capital or maintenancedredging campaigns)

The following figure shows ascreen shot of a vessel transiting inswell conditions. Red areas indicate'no-go' regions where the DUKC®

predicts the vessel to have insuffi-cient under-keel clearance due todynamic ship motions.

8. Reporting serviceAllows searching and retrieval ofarchived outputs, previous calcula-tions, errors and diagnostics. Allcalculations, errors, system messagesand diagnostics are logged and canbe queried if desired.

Underlying the core engines andservices are the various data storagecomponents. Data storage structuresinclude databases for vessel details,voyage plans, transit plans, met-ocean data and business messages.

Sample overlay of Go/No go areas for a vessel transiting in swell conditions.



5 CONCLUSIONS

The use of static rules at manyports needs serious considerationabout whether they are suitable andif all factors are understood. Theparadox of the static rules is thatwithout an incident a port’s staticrules may appear validated andconsidered safe. In reality, whereunderkeel limits are critical (whichis increasingly the case with everlarger vessels being launched), andconditions variable, there may betimes when the clearance is margin-al and the port has experienced anunknown “near miss”.

Recent developments in navigationtechnology make possible accurateplanning and the continualmonitoring, and control of the UKCof large vessels during transit alongshallow waterways. These decisionsupport tools, and the integration intonavigation systems, such as a pilot’sPPU, also allow the effect ofalternative speed/sailing options on

under keel clearance to be quicklyinvestigated by pilots and masters insituation where the passage does notproceed as planned. The informationthat is now available through adynamic system enhances thedecision making processes, of theport and pilot, and complements themaster/pilot information exchange.

Dynamic underkeel clearance sys-tems have a proven track record over19 years and its use will only increasethroughout the maritime industry.As the methodology builds on theconcept of a minimum clearancelimit that must not be breached, a dy-namic underkeel clearance systemseffectively controls the risk of a touch-bottom/grounding incident. This levelof risk cannot be achieved with staticrules because the clearances vary andare determined by the environmentpresent on the day.

For more information contactJonathon Pearce

[email protected]+447833517006

n

5.- CONCLUSIONS

OMC International Pty Ltd esuna sociedad con base en Aus-tralia que provee soluciones ma-rítimas de calidad internacionala los operadores y usuarios depuertos ubicados en vías nave-gables de poca profundidad. Lasprincipales actividades basadasen productos de la empresa sonel desarrollo, provisión, instala-ción y mantenimiento de solu-ciones marítimas para controlarlos riesgos operativos, mejorarlos beneficios de la navegacióncomercial y proteger de mejormanera el medioambiente, enespecial en áreas de alto peligro.Esta experiencia práctica inte-gral necesaria para generar pro-ductos también está al alcancede los clientes de OMC a travésde los servicios de consultoría.

OMC International está recono-cida en todo el mundo como laautoridad en el modelado y pre-dicción exactos del margen de se-guridad bajo la quilla de naves(UKC), y ha desarrollado el Sis-tema administrador de margende seguridad bajo quilla(DUKC®). El sistema DUKC® fueinstalado por primera vez en elpuerto carbonero de Hay Pointen 1993 y desde ese momento habrindado mejoras extraordina-rias en eficiencia y seguridad, re-duciendo al mismo tiempo loscostos en puertos de toda Austra-lia, Nueva Zelanda, y Europa.Entre ellos, algunos de los puer-tos graneleros, para contenedo-res y multicarga más grandes delmundo, por ejemplo, los puertosde mineral de hierro de Pilbaraen el noroeste de Australia.

Los sistemas DUKC® garantizanque se mantengan los márgenesde seguridad bajo quilla (UKC) entodas las condiciones, y durantemás de 17 años han asistido encasi 60.000 movimientos de naves,sin un solo incidente. Desde 1993los sistemas DUKC® han brindadobeneficios económicos a puertos ya usuarios de puertos por unmonto de más de AU $10.000 mi-llones en todo el mundo.

1.- Whangarei, New Zealand, 2003,when the existing rules failed after30 years in ‘safe’ operation.2.- OMC’s historical records showapproximately 95% of vessels areconservative, 4% marginal and 1%potentially unsafe 3.- DUKC® is the trademarked productof OMC International to determinedynamic underkeel clearances 4.- International Association ofLighthouse Authorities and Per-manent International Associationof Navigation Congresses5.- Underkeel clearance for largeships in maritime fairways withhard bottom; Supplement to Bu-lletin No51 (1985);6.- Factors include: Tidal residual(difference between predicted andactual tides); Tidal change duringtransit; Allowance for unfavourablemetrological conditions; Waterdensity; Squat (from ship speed);Wave response; Sounding errors; Se-dimentation, Localised phenomenasuch as standing waves. 7.- Loss of UKC = Tan Roll * Beam.However it should be rememberedthat two vessels, of the same di-mensions, but with differing sta-bility will react differently in thesame environmental conditions 8.- Squat is an hydrodynamic pheno-menon by which a vessel movingthrough water creates a localised

area of lowered pressure that causesthe vessel to “apparently increase indraught” and be closer to the seabedthan would otherwise be expected.It is approximately proportional tothe square of the speed of the ship.http://en.wikipedia.org/wiki/Squat_effect9.- Whangarei, 2003. Two vessels“Capella Voyager’ and ‘EasternHonour’ ground under existing staticrules, which were considered safe.10.- The limit/s can be found inPIANC, 1985 (Underkeel Clearancefor Large Ships in Maritime Fairwayswith Hard Bottom. Report of aWorking Group of the PermanentTechnical Committee II. Supplementto Bulletin No. 51 (1985)). The limitsused in a dynamic system are thePIANC’s Bottom Clearance and Ma-noeuvring Margin limits, but any sti-pulated minimum limit could be used.11.- DUKC® was first installed inHay Point, 1993. To date it hasbeen operational in 21 ports forover 19 years with 90,000 safe sai-lings,12.- The Port of Melbourne also un-dertook two independent risk as-sessment studies and these ex-tensive risk management studiesconcluded that the full complementof DUKC® navigation softwarewould significantly reduce the riskof large vessels grounding in portapproach channels.

Notes


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