PORT APPROACHES, BALANCING SAFETY AND COST

Transcription

1 PORT APPROACHES, BALANCING SAFETY AND COST by: F.R.. Kalff») V, Meenakshisundaram **} J,T,M. van Doom ***) ABSTRACT Throughout the world, Ports are in a constant state of change. Calling ships are changing in size, windage, manoeuvrability and cargo carried is becoming more dangerous and the overall safety aspect is a greater concern As a result Port Authorities have to reconsider and reevaluate the original design of their sea approaches and establish whether the Port access is safe.. If it is not, improvement works have to be planned and executed. Ports will have to plan for the future range of ships expected to call and those ports within a competitive environment will have to plan even one step further ahead New ports will face the same problems of planning for the future, but at the same time lack the experience Mariners already have in operating through existing Port approaches. Port approaches are a particularly interesting part of Port development, which brings together the Port engineer with maritime civil engineering experience, nautical experts and navigational aids specialists. The philosophies and tools for the design of safe sea entrances are gradually changing, largely due to environmental concerns, but also due to economic considerations, involving capital and maintenance cost. Notwithstanding these new tools, including various simulation techniques, it is not easy for the designers to find well balanced solutions In this paper design considerations are presented, which wil! aid in balancing safety with costs and these are elucidated for a new Port in the Bay of Bengal., For this Port two alternative port entrances were extensively studied, using the latest simulation techniques and design experience The new artificially protected port, located in a relatively moderate sea climate, will initially receive up to Panamax size vessels, while certain allowances for Suezmax vessels are to be incorporated *) Senior Port Planner, HASKONING Royal Dutch Consulting Engineers and Architects, Nijmegen, the Netherlands **) Chief Engineer, Madras Port Trust/ Project Director Ennore Coal Port Project, India ***) Nautical Expert, Maritime Simulation Centre the Netherlands, Wageningen 1. PORT APPROACHES FOR CHANGING SHIPS Maritime transportation of world trade is continually changing with respect to overall trade size, type of trade commodities, shipping patterns around the world, ship sizes and in the mode of shipding cargo commodities, Alt these changes and their impacts were not foreseen when many years or decades ago the approaches of the ports of the world were built. Port approaches should therefore be reviewed on a more regular basis in order to enable Port Authorities to incorporate these changes into their strategic planning. The review concerns the principal functions of the total approach and whether it meets the nautical requirements of the present fleet and of those ships expected to call in the near future, say 5 or 10 years time. The safe navigation to Ports is a subject which deserves our attention because increasing quantities of chemicals, petroleum products and other hazardous cargo being shipped in bulk or otherwise and our increased concern with the environment especially in coastal areas. Many Ports are currently reviewing the existing situation and assessing maritime safety with a view to formulating future shipping requirements and many more Ports are expected to follow Subsequent to a review a redesign of a port approach is likely to be required. Redesign normally consists of an iterative process, while various subprogrammes are being planned, executed and often modified during the design process. In this respect specific knowledge of environmental conditions, future shipping forecasts, aspects of dangerous cargo, local human values and ecologic resources, options for navigational aid, cost for reconstruction and the economic importance of the port and its trade, is required. The sea approaches of existing and also new ports, call for a match between nautical safety requirements of ships expected to call, engineering and construction efforts, to build and maintain the artificial part of the port access. Suggestions made in this paper might help to tackle such a task, while keeping in mind that the detailed scope of a redesign exercise will be tailor made for every Port having its unique circumstances and requirements

2 As an example, the authors experience with the design of a port approach for the new Port of Ennore in the Bay of Bengal is reported towards the end of this paper. 2 EVALUATION OF MARINE RISK IN CHANNELS In section 1 it was indicated that a design or redesign of a port approach is an iterative process. Gradually the design team works towards a final new lay-out. Although the process is gradual with an increasing accuracy two significantly different phases in the evaluation of marine risk, can be distinguished: initial planning phase; final stage. When (re)designing a channel the marine risk in the initial phase refers to required width (and depth) to facilitate the design traffic situation. In the final phase the actual risks involved are assessed and channel dimensions are fine tuned. Both phases require a significantly different approach.. In the first phase a more global approach is required, so the team working on the (re)design can check whether their ideas are feasible In the final (re)design phase it is more important to get insight in risks, and it is required to prove that the chosen solution works. It is therefor required to look into the problem on a different level of detail. Initial planning phase In this phase the (re)designed port approach is 'on the drawing boardb. Different alternatives are under consideration and the design team must get insight in the different aspects making the (re)design feasible or not. In an early stage a comparison between alternatives indicating better or worse might be sufficient. So the goal of a nautical study in the initial phase is to select the most promising lay-out from a nautical point of view and determine the required dimensions. The method followed should be sufficiently reliable to judge the safety of the selected lay out. - waves; - wind; - bank suction; -tugs. Entering the harbour is critical, when the environmental conditions are extreme or when the traffic conditions are complicated, simulations on a radar simulator are a good alternative In a fast time simulation model the ship is steered by an autopilot. This autopilot reacts on deviations from a predefined track. As this is a mathematical algorithm, which reacts always identical it gives the user the opportunity to compare the results in different conditions and for different lay-outs.. In a relatively short period the differences between various channel alternatives can be studied. The output of the model consists of the sailed track and all possible variables as a function of the track, e.g.: - speed(s) - rudder settings - propeller settings; - swept path. The swept path is the total width used by the vessel when sailing in the channel Simulation are executed for the design vessel(s), which are often the largest vessel allowed to visit the port (Figure 1) In most cases the channel will be used in a single lane situation, The simulations are executed for environmental conditions selected using the following criteria: Considering marine risks or the probability on accidents one can distinguish three possible causes of accidents: 1 environmental conditions (waves, wind or currents); 2. human failure; 3. ship failures In a first review of a design the first aspect is the most important one. It is assumed that the performance of the pilot is up to standards, and also the state of maintenance of the ship is reasonable This is acceptable when it is realised that these aspects do not vary largely between different alternatives. Applying these assumptions makes it possible to use fast time simulation models to compare alternatives. In these types of models all physical aspects influencing the ship's behaviour are included, e.g.,: - water depth influence on ship manoeuvring; - flow, direction and strength; Figure 1 Example of a fast time simulation into the port of Ennore, executed with the SHIPMA model

3 1. moderate conditions, which are representative for a large number of manoeuvres; 2. the maximum conditions under which passage is allowed and which still occurs regularly; 3. severest conditions which are the worst from a nautical point of view The first conditions are often irrelevant for the final design, but they are of importance as they give an illustration of an average manoeuvre, which will be executed practically every day. It will show the difference between manoeuvres under moderate and maximum conditions. The second conditions are selected on basis of the local climatologic conditions.. Wave height, wind speed and direction and flow velocity are maximal under which passage is allowed.. This maximum is often limited by the pilotage services The third conditions are the worst conditions from a nautical point of view.. They occur very seldom and are very difficult to cope with The actual number of simulations to be executed can often be limited to This is required to make a review of different possible lay-outs. The required channel width is determined using the result of the swept path analyses together with an estimate of the accuracy of the ship's position, steering width and a safety margin towards the banks The accuracy of which the ship's position can be estimated is largely depending on the aids to navigation It is a deterministic exercise resulting in a required channel width. It does not take into account statistical variations in the environmental conditions and in the behaviour of the navigator. Safety of channel passage is judged on basis of the actions required to keep the ship in the channel How much rudder is applied, what about the engine use, how often tugs are used. Especially the combination rudder use and engine use is essential The rudder is fare more effective when the engine is used. Consequently when both are used simultaneously at the maximum setting, the margins left are unacceptably small. In such a situation there is no room to cope with a misjudgment of the navigator or any other unexpected event and is thus unacceptable. Apart from rudder and engine also speed is an essential item when safety is considered Especially the speed when entering the port should be such that the ship can be stopped in time This speed is always related to engine use, consequently in difficult situations the speed will often be too large. Conclusions In a initial (re)design phase it is advantageous to use a fast time model The advantage of the fast time simulation are: results are comparable; easy to run; modelling can be very good. The disadvantage is that there is: no human influence; no statistical analyses; no berthing operations; no emergencies operations; Real time simulation When in the first phase of a project, fast time simulations are executed, there are mainly two reasons to repeat the simulation study on a real time ship manoeuvring simulator (Figure 2) Figure 2 Bulkcarrier inside the harbour basin of Ennore, view from the simulator bridge

4 Firstly to determine the risks involved, what is the probability that a ship will run aground or in other words, check whether the design meets preset safety criteria Secondly to incorporate the human element which is, to some extent, ignored in the fast time simulations. The simulator gives the possibility to let pilots, who are familiar with the local situation, execute the simulations on the simulator A simulator study can be divided in three steps: preparation, execution and analyses, which are discussed below. database preparations Before the actual simulations can be executed the simulator database has to be prepared for the particular situations The following needs to be prepared: A1 outside view; A2 mathematical ship models; A3 environmental conditions; A4 bridge layout. The outside view should contain all relevant data used for the navigation.. In practice this means that buoys, beacons, lighthouses, breakwaters and other characteristic objects in sight should be included in the outside view. Details are often important because these give additional information on the motion of the ship The mathematical modelling of the manoeuvring behaviour of the vessel can be identical to the modelling applied in the fast time model, e.g.: bank suction, water depth, currents and waves and wind. The simulator has more possibilities than the fast time model. It is possible to execute berthing and deberthing manoeuvres, which requires the modelling of tugs, fenders, mooring lines and winches Furthermore it is possible to study complex traffic situations This means that apart from the single lane traffic situation it is afso possible to study two or three lane situations. This is relevant in area's with a lot of traffic The environmental conditions can be chosen in the same way as for the fast time simulations. Which means that climatologic data, together with the ship characteristics will form the basis for the selection of the conditions. In situations when the port is used by a specific type of vessels or with specific equipment it is required to adapt the bridge lay out accordingly. execution of the simulations After the simulator database is finalised the simulations can start. The first day(s) on the simulator are used to familiarise the pilots, with: 1, the new situation; the type of vessel under consideration; the simulator.. Although the pilots are familiar with the existing port or the area under consideration, the simulator will give them the opportunity to find out whether the new situation is feasible or not. From this point of view it is important that the layout on the simulator is almostthe final layout When it is, for instance, far too narrow the pilots will get the idea that the proposed new lay out is impossible and frustrate the continuation of the project, even when the width is adapted afterwards. Apart from the new situation the pilots will often have to familiarise with the type and size of vessel under considerations. One of the goals of a port extension might be to receive bigger ships or a different type of ships, with which the pilots are often not familiar Also the simulator needs familiarisation.. Although simulators are realistic there are still differences with reality. The pilots need to cope with these differences. In general simulations under moderate environmental conditions are used to familiarise the pilots. These conditions also show to the pilots how manoeuvres will be executed under 'normal' conditions After familiarisation the research program can start. Most of the simulations will be executed during maximum conditions under which entry is allowed. In most ports this will be the maximum conditions under which pilotage is still possible, and in most situations this is a condition which is exceeded rarely.. It is also possible to study more complex traffic situations, In general the maximum ship to be received (single lane situation) will be of interest, but when smaller ships enters far more frequently allowing two lane situations, this might also be of interest. In order to get some indication about the safety of passage a simulation under a certain condition has to be repeated a number of times In case a deterministic analyses is applied six runs are sufficient, when the interest is focused on actual risks involved more runs are required. Generally in the order of ten runs are executed, Apart from runs under regular conditions, the consequences of failures can also be studied on the simulator However it should be realised that the effect of a failure in a narrow entrance channel is often dramatic. analyses The aim of the analyses of simulator runs is to get insight in the safety of channel passage or port entrance.. Safety can be divided in two aspects: 1. how much action is required to keep the ship on track; 2. how much of the available width is used.. The first aspect is related to engine and rudder use and the use of tugs (if applicable).. The criteria are identical to those used for the analyses of fast time simulations, When a limited number of runs is executed a swept path analyses is executed. With this analyses it is checked whether all runs have stayed within the channel boundaries. Together with the rudder and engine use this must give confidence that the channel is sufficiently safe, When enough runs are executed (ten or more) it is

5 are the aids to navigation sufficient or can they be improved In bends and at harbour entrances often more space is required and therefor the channel is widened locally at these locations Aids to navigation can be improved by using special positioning equipment like DGPS Thus the error in the position can be reduced significantly However if such a device is considered it should also be used during the runs on the simulator. The risk resulting from the simulator study refers to the probability of exceeding the channel boundaries. It does not give the probability of an accident resulting in damage to the ship, environmental damage or even a temporary closure of the port Not all aspects governing such a risk can be covered in the simulator study as such risk is largely effected by the probability of an engine or rudder failure and the location where it happens Figure 3 Results of statistical analysis of simulator runs, lines with 1% (---) and 10% ( ) exceedance probability possible to execute statistical analyses on the width used. Assuming a probability density function, lines with equal exceedance probability can be computed giving an indication how often the channel boundaries will be exceeded (Figure 3). This probability can be compared with a preset criterion.. The selection of such a criterion depend on the consequences of an exceedance of the channel boundaries, When the ship is carrying hazardous cargo, LNG for instance, or when the channel boundaries consist of hard material (rock) only a small probability can be allowed (once in 10,000 passages).. On the other hand when the surrounding area consists of soft silt and the channel is used by bulk carriers a larger probability can be accepted (once in 100 passages). Which criteria is appropriate for a specific situation is difficult to say Often the situation is compared with ports handling a similar type of cargo and with comparable soil conditions Criteria applied there are often the starting point for the selection of the safety criteria. Marine risk assessment The statistical analyses does give an indication about the risks involved during a channel transit. The width of the channel can be decreased when it is proven that the channel is too wide.. When the channel appears to be too small at certain locations it should be checked whether: this is only a local effect or actually valid for the complete channel; For the redesign of the port approach the width and depth of the approach are the first objective. But looking into safety of manoeuvres other objects in the area like: single buoy moorings, offshore islands, oil wells and pipe lines are also important. There are methods available to compute the probability of a rudder or engine failure at a certain location. Simulation techniques can be used to compute were the ship will end after such a failure.. Will it be in soft mud, or run into an offshore island, or anchor upon an oil well When these risks become unacceptably, large measures have to be taken to avoid this type of accidents. A solution can be escorting tugs which accompany the vessel into the port guaranteeing that the ship can be kept sufficiently under control. This type of escorting is operational in the gulf of Valdez (Alaska, USA). 3. DEVELOPING THE DESIGN THROUGH PLANNING ITS IMPLEMENTATION AND ASSESSING ITS COST With the simulation tools elucidated in section 2, the design or redesign of the port approach has obtained its major dimensions, in terms of alignment, width, depth and bend configurations, There may however still be two alternative designs, when both have their nautical merits and in general there might be scope for fine tuning.. Simultaneous with the simulation exercises the port planner shall study the implementation of the channel (re)construction and its ancillary facilities. Aspects of feasible dredging techniques, slope stabilities, implementation scheduling and completion period and nav aids design and installation are relevant in this respect. The realistic estimation of construction cost and possibly maintenance cost of the total approach system is of importance A significant cost difference between two alternative designs may tilt the balance towards one preferred design These total and annual cost are in general to be merged in the long term budgeting of the Port, The large amounts normally required to make the sea-access safe

6 for the future traffic, are not easy to incorporate in the expenses in the coming years. Queries from the Port's financial side may be raised and the right justification for the investments are to be provided The preferred design and any serious alternative port approach should be planned for implementation and the cost thereof be estimated realistically The following engineering and construction planning efforts will be required to assess the construction cost of a newly designed port approach: 1. estimation of quantities to be removed to construct the channel, 2. assessment of realistic cost for the removal of various types of earth/rock in the channel, 3. assessment of cost due to environmental requirements, as a consequence of grounding/collision risk, for special disposal techniques, or other protection measures of urban and ecologically sensitive areas in the vicinity, 4 designs for channel bound navigational aids of each alternative approach will have to be developed, 5. assessment of the installation cost of aids to navigation. 1.. estimation of earth/rock quantities to be removed In order to determine the quantities of material to be removed, detailed bathymetry is required. Furthermore a good insight into the geotechnical characteristics of the subsoil along the channel alignment should be obtained by executing a detailed investigation programme.. 2 assessment of realistic cost for the removal of earth/rock in the channel The possible dredging methods or rock removal techniques may be assessed by an experienced port engineer. He will do that on the basis of the geotechnical investigations, local wave conditions, availability of space for dredging operations and spoil disposal options Finally the cost of constructing the artificial channel shall be assessed 3 assessment of cost due to environmental requirements Requirements to protect human lives and to protect ecofogically sensitive areas in the vicinity are rightly so, being seriously considered all around the world these days. A justified compromise between the protection of humans and the environment on the one hand and the economic interests of a Port on the other hand, should be the goal of all concerned The extent of pollution of dredged material and the impact of the disposed material, either offshore or on land are to be investigated and assessed The London Dumping Convention, which is still in a process of further crystallisation to find a balance between the protection of the environment and economic interests, is an international guide in this respect. 4. designs for channel bound navigational aids Channel bound navigational aids have become increasingly important, because a o., modern electronic positioning systems could facilitate vessel negotiations more accurately and result in savings in channel dimensions and implementation cost. Leading lights, marker buoys, Racon and other conventional aids are normally being provided, either as a primary system or as a backup 5. assessment of the installation cost for the necessary aids to navigation. The cost for these channel bound navigational aids are normally small in comparison with the channel construction cost, but an assessment is recommended for inclusion in the total cost of the approach The cost for the maintenance of the new port approaches, if significant, is to be estimated for inclusion in the comparison as well. To assess this cost the following engineering efforts are required: A estimation of annual siltation rates and quantities in various stretches of the channel, with a distinction between sandy material and fines B programming of channel inspection surveys, programming of maintenance dredging campaigns by dredging techniques adequate for the prevailing circumstances. C. assess the cost of inspection surveys and dredging campaigns, either through contracting or execution by authority owned and operated equipment, D. design of any siftation reduction measures and evaluation of its effectiveness in comparison with regular dredging campaigns; assess its construction cost, E assess maintenance and repair cost of the navigational aids, A.. Morphologic processes, either along the coast or in a river estuary, are difficult to quantify, due to their annual fluctuations and difficulties to measure them directly in nature with reasonable accuracy. The best tools to assess any changes in the process through human interference are mathematic models and not physical models. In order to quantify these processes with a reasonable accuracy, the advice of the best morphologic specialist in this field are required B, On the basis of what the morphologist predicts, a programme of monitoring through regular bathymetric surveying is required to ascertain that the minimum specified depth in the channel is available at all times.. Also a programme of dredging is required on the basis of which the cost of maintaining the channel to the specified depth can be estimated Options for different techniques are to be explored, but trailer suction hopper dredgers will in most cases be the most suitable equipment. C. To estimate the cost of B) above, the channel Authority will have to make up its mind, whether the surveys and the dredging are to be executed by Contractors or by his own department. In many cases the contracting in accordance with carefully specified contract conditions are to be preferred for flexibility in timing of execution and/or execution

7 techniques. Also in a time when the word of privatisation is on every Port director's lip, if his Port has not gone for privatisation long ago, the contracting of these services provides an easy start for privatisation. Scrupulous wording of the (international) Bid Documents may call for specific and up to date experience. Siltation reduction measures or maintenance dredging minimization programmes have been developed and successfully implemented in many ports For new approach channels they should at least be considered and evaluated. The fine tuning of these measures and programmes is normally realized during the initial years of maintenance Estimates of the benefits and costs should however be made at the initial stage, to incorporate them in the overall cost picture. The maintenance cost for navigational aids should normally be kept at a low level, however marker buoys should be lifted from time to time and the availability of a ship with hoisting capabilities should be considered. Either the channel authority or outsiders could do the job; both will be at a cost, which should be incorporated in the overall cost estimate. Certain parts of the nav aids require replacement and consequently the need for spare parts is to be considered., in countries with closed economies, the solutions for having spare parts available when they are needed, are difficult and costly. For Port approaches of existing Ports, which are considered to be slightly unsafe for the present traffic and particularly unsafe for the future traffic, a redesign of the port approach is necessary and similar efforts as outlined above for a new port approach, should be applied. Typical differences in engineering efforts for the assessment of the construction cost are: 1 The experience of the pilots to negotiate ships through the existing channel, allows a reasonable assessment of the nautical constraints.. As a starting point this would normally indicate ways of improving the channel Simulations for the new design ship or ships will produce the new requirements for the dimensions of the approach. 2 The quantities to be removed for the reconstruction of the channel may be estimated on the basis of previous construction experience and new information on soil conditions and modern earth/rock removal techniques. 3 Ecologic considerations will also have a much more important impact on the channel redesign and reconstruction, than it had on the original design In this respect no differences are anticipated with the design of new approaches.. 4. A substantial part of the channel bound navigational aids are likely to be replaced and modernized because of new developments in this field. Modern navigational aids together with Vessel Traffic Services (VTS) might contribute to a safer navigation in the approach to the existing Port. Upon completion of design efforts identified in this chapter, the design team will be in a position to estimate the cost for alternative designs or redesigns, whichever may be the case. The optimisation process of the (re)design and the process of approval by the decision makers may be pursued further and section 4 will provide additional tools in that respect 4, BALANCING COST AND SAFETY Marine risk has been dealt with in section 2 and certain safety aspects have been assessed, while these and other safety aspects require a final iterative balancing with the cost of the (re)designed port approach scheme. In this final stage, where various departments of the Channel Authority and others, will have to give their consent and approve to invest in the construction of a new or revised channel with its ancillary facilities. Acceptability of the proposed scheme by organisations outside the channel owner's organisation is a time consuming process. Facilitation and speeding up of this process may be by evaluation of the following 5 aspects of the final design process to bring the nautical and environmental safety of the approach in a proper balance with cost of the new scheme. 1, availability of an adequate and complete data file of relevant environmental phenomena at the channel location, 2. use of advanced and classified simulation models for ship manoeuvring, 3 restrictions in channel operations, scheduled by the channel authority, when certain environmental criteria are exceeded, 4. realistic assessment of rather imponderable design aspects, 5 in depth comparison with three existing approach channels with similar traffic requirements. 1. data file availability of environmental phenomena For the nautical simulations and also for the (re)design of the approach environmental data on tides, currents, waves, wind, sea or river bed, etc are required The quality and reliability of these data in terms of statistical occurrence, extremes, seasonal variations is often lacking. In that case the input in simulations and design are normally conservative, (what else can the designer do?) and consequently this leaves room for improvement when detailed data are available The collection of a good environmental data is at a nonnegligible cost, mainly due to the installation of measurement equipment and the recordings of the various phenomena Moreover most of the recordings have to be sustained for a year and often longer. An early start with a programme for proper collection of

8 these data is advisable and often pays oft by proviaing a thorough optimization of the approach It is a tool, which can be used to keep the cost down in case of an earlier overestimation of the outside conditions and to bring safety on the required level in case of an earlier underestimation of the outside conditions 2 use of advanced and classified nautical simulation models The present practice to design the horizontal dimensions of the Port approaches on the basis of nautical simulations, is well accepted. The application of either fast time or real time simulations and the quality of these tools and/or facilities are all essential to arrive at a realistic picture of the future negotiations through the approach When in doubt a review of the total process or an additional simulation programme with a different tool or with different pilots, may lead to a more realistic picture of the port approach safety. This may also lead to a better balance between safety and cost and the acceptability by the decision makers may well improve 3. Restrictions in channel operations Restrictions in the operations of the approaches has been dealt with during the ship simulations in section 2. With these ship simulators a quantification of unsafe conditions, calling for channel closure is possible. If however channel closures for longer periods are considered, the acceptability thereof is a matter to be dealt with at this final stage Complete closure of port approaches during certain periods of time are a reality in many ports. For some it is only during one day per year when a cyclone is passing by; for other ports with a large tidal range it may be a daily occurrence when the largest range of ships are programmed to enter and leave the port on top of the tide.. Programmed downtime is a possible means of balancing cost and safety in all its aspects. Expanding Ports may be restrained to continue accepting programmed downtime, but economic impact calculations normally prove their effectivity. Through its channel policy certain restrictions are to be enforced by the Port or Channel Authority either on the basis of predicted or measured environmental phenomena. If accurate predictions can be made, this may provide a suitable basis for the scheduling of channel closure. The vertical tide phenomena is a relevant example in this category, although a tide gauge in the harbour may provide feed back for the closure periods Channel closures due to phenomena like currents, waves and wind can only be scheduled on the basis of continuous measurement at critical spots. It may therefore be necessary to instal recording stations on structures at relevant locations at sea. Continuous data transmission by radio will allow the Channel Authority to limit the channel closure as much as possible and still meet the safety criteria required. Poor visibility has been a classic reason for not negotiatina a channel Modern navigational aids both on board and along the channel have reaucea its negative impact However during extremely poor visibility, pilots and captains normally decide to wait until the situation clears up To enable a very large ship or one with hazardous cargo to safely navigate through a channel with two way traffic, the Channel Authority might decide that only one way traffic for that particular ship is allowed Traffic in the other direction is consequently blocked during the passage of that particular ship 4 assessment of imponderable design aspects Apart from the direct design aspects of the channel, there are more distant aspects which have an impact on the design criteria and the acceptability of channel operations in a (re)constructed channel. Acceptability in this respect, is by the owner, who has to put up the money, the Authorities, who have to give approval for construction and the general public, who have to live in the adjacent environment. The imponderable aspects could be: the assessment of a permissable risk of grounding on the channel bank or the permissable risk of collision between two ships possibly carrying hazardous cargo, while a residential area, an environmental sensitive area or a recreational beach is in relative close proximity the behaviour of humans handling ships in the approaches, are normally predictable and controlled.. However in very rare cases, the behaviour is not so predictable with dramatic consequences Unfortunately these rare cases determine the statistical safety of an entrance channel. Worldwide the statistics of human failures in this respect are scarce and quantification remains difficult. Setting the statistical criteria for permissable grounding be it one passage in 1000 or one in , is primarily based on judgement. To estimate the impact of a grounding or a collision on urban and ecologically sensitive areas is even more imponderable.. These above aspects can be facilitated in the operational conditions by: training of pilots, operating a Vessel Traffic Service (VTS), ship escorting by tugs along critical passages In busy areas or in areas with environmental sensitive conditions a VTS or VTMS, Vessel Traffic Management System can provide support, when the operations tend to go out of control. The VTMS can regulate the traffic, give weather forecasts, determine weather windows, etc For a final assessment of the so called imponderables, we will realize that the figures used in the design are ail relative and not as accurate as we would like. To convince us of the right criteria for the final design, an analysis as suggested in 5 below might prove useful.

9 5 in depth comparison with three existing approach channels Approach channels to Ports around the world can all be considered as simulators at prototype scale, where a very large number of approach negotiations have been performed. We can learn from them in respect of their safety. One might initially feel restrained by a lack of grounding/collision records, because only a few Ports make these records available. There is a way around it, and it is worth tapping this large resource The way around it, is based on the fact there is no Port in the world, which can afford to have an unsafe entrance Some approaches, which might have had problems of grounding or collision can not afford to do nothing about it. If they don't improve their channel, they might appear on the black list of the ship insurance companies and no Port in the world can effort that for very long. These odd approaches, which are turning out to be less safe, will consequently work on an improvement scheme, It is estimated that these odd approaches are less than 1 % of all worldwide approaches. In order to reduce the chances of selecting an odd approach with some potential dangers, it is recommended to select say three existing ports for comparison with the new (re)design. Best results will be obtained when the comparison is made with approaches with similar traffic in terms of ship sizes, channel capacity, one or two way traffic and movement of hazardous cargo. The physical differences between the new (re)design and one of the three existing approaches, like alignment, bends, depth and environmental conditions are to be brought to a comparable situation by fast time simulation techniques. The dimensions of the three existing channels are consequently translated in to dimensions of the approach under design considerations. If the translated dimensions of the three existing approaches are significantly smaller than from the (re)design, there seems room for reduction of the approach design To perform the above exercise the collection of traffic and environmental data of say three approaches might turn out to be hard. Statistical records of ship movements by Lloyds, atlases prepared by the Admiralty, Pilot Association and others, together with information on direct request from relevant Ports, should, with some effort, lead to a sufficiency in information to perform the translation by fast time simulation. With the above method it seems that the real practice of navigation in shallow waters can be used to our advantage for the safe design of new approach channels or for a re-assessment of existing channels. Experience with this method is still very limited, but through the worldwide liberalisation and the increasing readiness of ports worldwide to share information, it is expected that this method will be used more frequently Figure 4 Alternative Port layouts studied for ENNORE

10 5.. CASE STUDY: APPROACH TO NEW PORT AT ENNORE, INDIA The Madras Port in the Southeast of India, was built in the 19,h century and its present location squeezed between the sea and the metropolitan city, is constrained by lack of space and port capacity in general. A new satellite Port is inevitable and studies have been going on since the mid eighties at a site 20 km north of Madras. A feasibility study and a Detailed Design for the First Phase of the Ennore Port Project, to handle 16 million tons of coal per annum, have been performed by HASKONING Royal Dutch Consulting Engineers and Architects. The study was performed for the Ministry of Surface Transport, while the Design and subsequent Supervision are and will be performed for the Madras Port Trust as the owner of the new Port. The Asian Development Bank is providing a loan for a major portion of the Project. The design ship for the First Phase of port development is a Panamax bulkcarrier, say DWT. The Port requires breakwater protection for reasons of tranquillity and littoral drift, and the harbour mouth between the breakwaters is 1.5 km from the existing coastline The approach channel is aligned between the harbour mouth and the natural bed contourline of CD 16 m, which is about 3 km from the existing coastline assessment of the channel dimensions taking into account about 10 to 15 boundary conditions, which are site specific These initial designs are shown in Figure 4 For the fast time simulation of the layouts with a NE and S entrance, shown in Figure 5, the classified SHIPMA model has been used to perform 25 runs. A majority of runs has been executed under critical environmental conditions The simulated vessels could be kept under control without much power or large rudder angles, which means there is a relatively large margin in manoeuvring capacity. It was further confirmed that the stopping distance was adequate and the basin dimensions are ample. The simulations indicated that the dimensions of the NE entrance with a width of 250m in both legs of the channel, including the bend over 25, are safe, The straight approach of the Southern entrance, originally 150 m wide at the bottom, turned out to be relatively small and 180 m was recommended. Both layouts were considered safe for navigation, even for ships which were poorly maintained and which can not be excluded from calling at Ennore occasionally. The NE entrance had however the disadvantage of the shoal northwest of the channel, which poses a potential threat, when negotiations go out of control. The alignment and the dimensions of the entrance channel to the Port, but specifically the orientation of the channel has been a subject of concern and major debate. The orientations, which have been seriously investigated are from East, from Northeast and at a later stage from South., Apart from the very important nautical convenience to negotiate the channel, the following aspects have also played an important role in the final decision for a Southerly entrance: wave penetration in the harbour basin, littoral drift, mainly from south to north, expansion for future development, including ships up to Suezmax, channel investment and maintenance cost An approach from East to West has been studied at the feasibility stage and was mainly rejected for non nautical reasons An entrance from northeast has been seriously investigated, because the Port Trust and especially the Marine department, was familiar with such an entrance orientation in the Madras Port. A southern approach proposed by the Consultants in the design stage, was initially criticized for its vulnerability in respect of littoral drift. Figure 4 shows the three layouts, which were studied.. Fast time simulations using the SHIPMA model programme, were performed for all three alternative approaches The real time simulations at MSCN, Wageningen, the Netherlands were performed for a northeast and a southerly entrance. The initial designs were prepared using the conceptual design guide of PIANC/IAPH/IMPA 1995 [1], This guide based on worldwide experience is practical for an 10 Figure 5 Port approaches tested by real time simulation

11 The real time simulation executed for the two layouts at the MSCN facilities in Wageningen, has helped substantially to reach agreement between MPT's Nautical wing, the Project Directorate and the Consultants Four pilots and officers from MPT's Nautical wing performed the simulation runs. The realistic conditions at the bridge in the simulator turned out to be effective for ironing out the differences concerning safety, which prevailed earlier. It was concluded from the real time simulation that for the NE entrance the dimensions of the bend had to be adjusted and the outer leg's width be reduced to 200 m. For the straight Southern entrance the simulation showed that a bottom width of 170 m will be safe and convenient to negotiate. Based on future projections regarding shipping and to provide extra safety for the pilots, who are initially unexperienced with the new situation, the final bottom width is designed to be 250 m (Figure 6) The manoeuvring basin of the final layout is better protected against waves, so tugs can practically always operate. Finally the construction cost for the layout with the Southern entrance is 12% lower in respect of both capital and maintenance dredging and breakwater construction The suggested admission policy is up to a significant wave height of 2 0 m, a northerly directed current of 0.6 m/s, a southerly directed current of 0,5 m/s and a windspeed of BFT 7, From the five recommendations made in the previous chapter to balance safety and cost, the first four were applied for the ultimate design of the Ennore Port All four have contributed to a keen design of the port layout and the approach channel and the following observations are relevant in this respect: 1. At least five survey and investigation programmes were implemented in order to have a good understanding of the bathymetry, tide, current {velocity, direction), waves (wave height, wave period, wave direction), seabed material, subsoil, wind and visibility. Relevant surveys were performed over a long period of time and some were overlapping, allowing checks on time effects, if any The accumulated value of the surveys is estimated at US $ 6 million.. A well justified investment for a project with a first phase development of an estimated US $ 250 million and subsequent development of two to three times that amount. 3 Due to the good visibility, moderate wave and wind climate, moderate to low currents and cross currents, the operational restriction to be enforced by the future port Authority will be very minor. The channel will be closed an average of once per two years due to cyclones Due to visibility constraints the channel will be closed, an accumulated 1-2 day(s) per year During the northeast monsoon period (November, December) the significant wave height will be higher than 2,0 m and pilot transfer services will be out of operation during an accumulated period of theoretically less than 1 day but practically 2 days per year Consequently the port approach will be closed for 4 days per year, which is quite acceptable for the initial coal transport envisaged but also for traffic foreseen in the next decades. 4. The only environmentally sensitive area in the vicinity is the Pulicat lake, some 17 km north of the Port location. The lake, which is connected to the sea by a small inlet, might be the first potential intake of any pollution, if this would float at sea or be suspended in sea water. The distance and the low currents would make pollution of the lake a very remote chance. Moreover, the coat which will be brought in wil! not be a threat at all in this respect. Only spilled bunker oil seems a very remote potential threat, which can be mitigated. In conclusion it may be noted that the nautical design of the new Port has been prepared in accordance with the latest views and using the best tools available The authors are convinced that the design is safe and not calling for any unjustified investments or operation expenses In other words a good balance has been struck between nautical safety and investments, be it that a small part of it is justified for the future use of the port beyond the first phase. Ultimately the "proof of the pudding is in the eating", but the authors are too impatient to wait 4 years for construction to be completed and another 4 years for the port operators to confirm that the nautical safety is OK. The simulation models used are state of the art and the real time simulation has in particular helped to convince the Port Trust to deviate from their historic concept of a northeast entrance. On the basis of the fast and real time simulation, channel dimensions could be established, which were close to the final design. References: [1] PIANC/IAPH/IMPA, Approach channels, A Guide for Design,

12 Figure 6 Final layout Ennore Port 12