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It is important that the survivability performance of a tanker is assessed. The survivability of a ship was investigated probabilistically by the the 'Pollution prevention and control' (POP&C) project considering all possible damage sizes. This required the probability of the damage extent for all pertinent incident categories (grounding, collision, contact, structural failure, fire and explosions) to be determined.
Three situations may arise following an accident leading to breach of watertight integrity; the ship will capsize as a result of loss of stability, the ship will break up and sink as a result of loss of structural integrity or the ship will remain afloat having suffered some sinkage/trim. The immediate concern would be regarding the loss of stability since this would result in rapid capsize, whereas loss of structural integrity may be a more gradual event.
The statistics of damage extent for collision and grounding were collated and consolidated in the 'Harmonization of rules and design rationale' (Harder) project for all ship types, making it the most comprehensive data available for collision damage. The POP&C project partners have investigated whether the Harder database can be utilised for tankers only and for both collisions and groundings.
The key findings of this investigation are:
1. For Aframax tankers the collision and grounding damage extent distributions developed by 'Marine pollution' (Marpol), modified to limit extents for collision damage length and collision penetration for large tankers, should be used. The proposed 'Safety of life at sea' (SOLAS) harmonised distributions, derived from Harder statistics for all types of ships, are not as good a match for the tanker only data. For smaller tankers these distributions will underestimate collision damage penetration and length and alternative distributions would be more appropriate.
2. For the purposes of the POP&C project it is recommended that the Marpol statistics for collisions be used for the Aframax tanker investigation when an allision (contact) takes place. The probability of having an allision can be treated separately from collisions, and the consequences of the damage may be quite different depending upon both sea conditions and environmental constraints. Note that there are very few allisions in the Harder database for which extent information is provided, and the information available is dominated by small ships.
3. Fire and explosion and structural failure data from the POP&C accident database proved insufficient to develop probability distributions for damage extents. However, efforts were made to determine the probability of loss of watertight integrity and damage leading to pollution. Also, probability of loss of lives / injuries due to fire and explosions, and structural failure was also accounted for.
4. For fire and explosions, the location of the damage was identified by considering areas/ compartments with specific functions such as engine room, pump room, boiler room, accommodation area, ballast tanks, cargo and slop tanks, etc. where the likelihood of such hazards is high. For structural failures, the location of the damage was identified as in cargo area and in non-cargo area.
In order to determine survivability performance of a vessel, survivability factors that are suitable for assessing tanker ships after damage are investigated. The comparison shows clearly that Marpol damage survival criteria set the lowest acceptable level of risk.
A series of damage cases are derived, each of known probability, and evaluated to assess survivability, and also oil outflow. Historical data reveals that Aframax tankers have a high rate of survivability given loss of watertight integrity (LOWI). To take advantage of related data associated with oil spills for calibration purposes and to provide consequence data for the overall risk assessment, the methodology has incorporated oil outflow evaluation.
A number of case studies for various single and double hull Aframax tanker configurations have been performed. These case studies provide a comparison between the design types, and also data to be used in the calibration of the methodology throughout the project.
The comparison of the historical data with the output of the analysis was done taking into account:
- the probability of being in a given loading condition at the time of the accident;
- the probability of being in a given tide during the time spent aground;
- the side outflow adjustment factor;
- the percentage of single hull versus double hull involved in grounding or side damage.
The methodology captures the behaviour of the Aframax fleet in accidents leading to spills resulting from collisions and groundings.
For Aframax tanker accidents, the probability of losing the structural integrity of the hull in the event of losing the watertight integrity of the hull was investigated by the European project 'Pollution prevention and control' (POP&C). The structural reliability of a damaged tanker was assessed considering global and local loads acting on the hull structure considering all relevant limit states. To achieve this, the following steps were considered.
1. Identification of the damage scenarios for the detailed structural analysis
This requires, the description of the damages sustained by the ship but also the definition of the loads acting on the ship pertinent to the sea state at the time of the incident. These two types of information are required to perform modelling and structural assessment.
However, an accident scenario is a complex set of events which is not limited to the size of the damage and to the loading condition. Hence a general methodology was developed in order to describe in a structured manner a scenario of an accident. This led to the definition of an exhaustive list of damage scenarios. A scenario was described as a sequence of events starting from the initiating event to the end event of interest that can be divided into five main blocks.
2. Non-linear dynamic collision analysis for both single and double hull tanker Existing collision and grounding damage statistics are based on historical accident data mainly for single hull tankers and do not realistically represent double hull designs. It is expected that collision and grounding damage statistics for double hull tankers will be different and the use of existing damage statistics may lead to unrealistic conservatism.
Therefore, rational damage extent statistics for double hull vessels from the existing data on single hull vessels have currently been developed by carrying out dynamic collision analysis.
The approach adopted is as follows:
A number of collision scenarios are applied to single hull tanker. For each of the scenarios the selected collision speed, angle and orientation, and the collision energy and damage extent are recorded. The same collision scenario (i.e. same contact speed, angle and orientation) is then applied to a double hull tanker resulting in different collision energy and damage extent. Using the existing relationship between the damage probabilities and damage extents for single hull tankers, an attempt was made to generate damage extent probabilities for double hull tankers. These damage extents may be used in other work packages of the POP&C project in assessing damaged stability and structural integrity and oil spill quantity.
The non-linear Finite Element dynamic analysis code LS-DYNA was used for this study.
3. Non-linear residual strength analysis on both single hull and double hull tanker for the selected limited number of scenarios. Probabilistic residual strength assessment for damage to ships requires a simplified, fast and accurate method of analysis so that a large number of scenarios can be evaluated within a reasonable time. Such a simplified method is under development within the POP&C project. It is necessary that such a simplified method will have to be validated and verified for complicated scenarios against detailed numerical calculations using non-linear finite element modelling and analysis.
For this reason, seven damage scenarios per ship type (i.e. single and double hull tanker) have been considered: three collision cases, three grounding cases and one explosion. Detailed numerical calculations are currently being carried out by considering three hold models using ABACUS non-linear finite element software.
4. Development, validation/calibration of a simplified residual strength assessment numerical method to be able to handle a large number of damage scenarios. The specific objective was to develop a methodology based upon the usage of relatively simplified models that will assess the probability of structural failure following initial damage and was to draw upon the work of the previous tasks.
The methodology for undertaking such an analysis was outlined with each of the possible methods being considered. Two cases studies have been presented - one single hull tanker Single Venture and one double hull tanker, Double Venture.
For the Double Venture analysis, eighteen damage cases were defined based upon the analyses carried out previously. The ultimate strength of the hull girder was compared across the range of methodologies used by partners in WP4 - these being 3-D finite element analysis, 2-D progressive collapse analysis and more simplified, and hence approximate, methodologies. Biaxial bending was also investigated.
The probability of failure was developed using a 'First order, second moment reliability methodology' (FORM) with a generic limit state function. The probability of failure was found for the Double Venture accounting for the damage cases, the variation in the still water bending moment and the wave-induced bending moment in the five sea areas being considered by the project. Both the full load and the ballast conditions were considered. A similar study was undertaken for the Single Venture. The two cases studies were then compared.
The three possible events described in work packages 3 and 4 of the 'Pollution prevention and control' (POP&C) project are loss of damage stability/sinkage, loss of structural integrity or ship stay afloat. These will lead to oil outflow, loss of property (vessel and cargo), and loss of lives/injuries.
An environmental consequence analysis model, referred to as the US Marine Board study where a non-linear consequence function was generated for varying amounts of oil spills based on a reference oil spill by considering only physical parameters of the oil spill, is utilised to assess the environmental pollution risk. The use of this consequence model was decided based on a POP&C study where the validity of consequence function introduced by the US Marine Board for EU waters was confirmed.
The nonlinear consequence function used in the methodology is based upon four measurements:
- area of slick,
- length of oiled shoreline,
- area of oiled shoreline,
- toxicity in the water column.
Although the focus of the POP&C project is on the environmental risk as a result of tanker accidents, risk to lives and risk to property will also be determined. For this reason, consequences of lives lost and property loss must be calculated. Consequences of main tanker hazards to human lives and property were analysed mainly from the historical data of Aframax tanker accidents.
In relation to the development of acceptability criteria for the three risk components (environmental risk, risk to lives and risk to property), after investigating the existing work such as the Sveso directive and Barpi scale for three accidents with severe consequences, the project decided that it would be restricting if these three risk components are combined and it would be more appropriate to consider acceptable criteria for the risks individually.
A body of work already exists on the acceptability criteria for individual risk (risk to lives) and the risk to property will be much lower compared to the other two. As such, efforts have been focused on the development of acceptability criteria for the environmental risk. The project therefore went on to detail an 'As low as reasonably practical' (ALARP) region for oil spills based on comparing the pipeline and offshore industries to the tanker fleet. Some corrections to the ALARP region were needed to take into account the huge benefits that tankers bring to the world.
POP&C further investigated the proposed ALARP region against oil outflow as a consequence and also analysed which category of accident events contributed the most to the Aframax tanker fleet's risk level. Further analysis also confirmed that the key to reducing the intolerability of tankers is to control the grounding accidents and, to a certain extent, the non-accidental structural failure accidents.
For quantitative assessment, methods for developing frequency of oil outflow and consequence of the spill are applied to accidents resulting from collision, contact, grounding, non-accidental structural failure, fire and explosion to evaluate the environmental risk of the current fleet of Aframax tankers and to place it in the context of the reduction of risk from single hull tankers to the fleet as it will be characterised at the completion of the phase-out of single hull tankers. Environmental risk was derived by multiplying the frequency of oil spills by the consequence of the spill. Consequence is evaluated on the basis of mean oil outflow and using a non-linear function that accounts for a reduction in consequence per additional tonnes spilled as spill sizes grow.
For each of the individual six major accident categories, we considered three possible outcomes or scenarios: ship breaks into pieces (loss of structural integrity), ship loses her stability or ship remains afloat. The evaluation of the consequence is different for each of these outcomes. Therefore, total number of accident scenario is 18. Moreover, for each accident category, a probability of occurrence is assigned either from historical data or any probabilistic estimation using simulations. However, not all incidents lead to loss of watertight integrity and as such the probability of loss of watertight integrity per accident category needs to be incorporated.
A series of case studies evaluating the application of risk control options (RCOs) and pollution control options (PCOs) utilising information from other workpackages were conducted. These include alternative tank arrangements, alternative partial loading approaches, increased scantlings and the effects of updated damage extents based upon analytical work. In addition, case studies such as inserting ballast tanks and application of dynamic underpressure to cargo tanks have been investigated where both qualitative and quantitative assessment were made. The use of the quantitative environmental risk assessment methodology in risk-based design and optimisation process was also demonstrated with examples.
A final case study evaluated a conceptual Aframax tanker that applies some of the lessons learned in the course of the POP&C project. Whereas this design is at an early concept level, all arrangements and systems have already been applied in the industry. Risk reductions in the order of 35 % are achievable. Optimisation of this design is certainly possible. Assessment of the cost-effectiveness of the design requires evaluation of the impact on construction, operational and fuel costs. However, there is a clear indication that significantly more environmentally friendly tankers are feasible.
The objective of this study within the 'Pollution prevention and control' (POP&C) project is to determine a risk reduction index representing the effects of application of operational measures on the risk of oil spills from tanker vessels. Thus, the first step of the study is to identify and assess risk control options (RCOs) that could be chosen in order to avoid accidents leading to oil spills.
In order to determine the most feasible and efficient RCOs, a selected number need to be evaluated using simulations. To obtain RCOs that could be assessed from an operational point of view, four criteria have been considered which are: operational feasibility, risk reduction efficiency, decision support tool implementation, and simulation ability.
A simulation-based decision support tool (DST) was developed which provides a computer-based online early warning system for grounding avoidance. The tool consists of three main parts; a signal interface for input of sensor data from the ship, a mathematical software function for calculating the clearance at predicted ship positions ahead of time and a chart-based graphical user interface for user control and presentation of the predicted results. The tool itself, i.e. the software program, was installed, tested and evaluated at the bridge simulation facility of STC in Rotterdam.
The simulator experiments on prevention scenarios study were based on the following objectives.
- To develop simulator scenarios for a study of the relevancy of DST tools used for the reduction of collisions and groundings with sea going ships causing marine and coastal area pollution;
- To validate the developed scenarios that will be used to investigate the relevancy of a DST tool with a ship path prediction feature which, should reduce the probability of a grounding in shallow water areas;
- To validate the developed scenario that will be used to investigate the relevancy of automatic identification systems (AIS) for reduction of frequency of collisions between ships at sea.
The proposed scenarios were used to investigate whether DST and AIS could improve the safety of navigation of tankers to reduce the risk of collisions or groundings. Based on the executed runs, the first impression of the navigators was that the DST tool will be able to improve the accuracy of navigation under more critical circumstances.
To reach an acceptable standard for a study regarding these tools the following recommendations were established;
Regarding the simulation tests :
- at least six runs per scenario with and without the DST tools should be made;
- information on the track, speed, revolutions per minute, rudder and off track distances for further numerical analyses should be stored;
- navigators should fill in a questionnaire after each run to establish their findings;
- the tanker should sail in an area where more realistic tidal water levels can be simulated. This can be done if the DST uses the depth information of the simulator.
The DST tool
- A DST tool where the predicted path can be superimposed on the 'Electronic chart display and information system' (ECDIS) and 'Radio detection and ranging' (RADAR)/ 'Automatic radar plotting aid' (ARPA) system is required.
- The best option is an ECDIS where all the information of ships in the environment from the RAD/ARPA and AIS together with the DTS is presented.
- A reliable and accurate ship mathematical model is essential for any loading/draught condition of the ship.
- The predicted path of the DST should be based on the same depth information as the ECDIS and retrieved from the ECDIS. Then simulation can be done in any relevant area.
- There must be an input menu on the DST tool for the actual tidal water level which is clearly shown on the ECDIS.
- The predicted path by the intended rudder order should be presented by a trial manoeuvre similar to the RADAR/ARPA systems.
- The DST should not show predicted paths for small rudder orders caused by the autopilot on a steady course.
-Proper path prediction information should be available under wind and current circumstances.
Alongside bridge simulations where a limited number of simulations can be made, fast track simulations were carried out running the same DST tool on a personal computer. The effectiveness of a number of simulations based RCOs in terms of reduction in frequency of occurrences was determined.
An integrated methodology has been implemented through existing commercial salvage and naval architectural software packages, plus additional tools developed to provide a probabilistic survivability and oil outflow analysis capability.
Existing, commercially available, salvage response or naval architectural design software (e.g. Hecsalv, NAPA) can be used to model and evaluate individual damage cases including analysis of damage stability, oil outflow and residual hull girder strength after structural damage. Hecsalv has been made available to the 'Pollution prevention and control' (POP&C) project partners for use in this project.
A probabilistic survivability/oil outflow tool to develop damage cases from collision and grounding statistics has been developed. This tool also develops the oil outflow amounts for each damage case, and statistics for all damage cases such as mean outflow, probability of zero outflow, and cumulative distributions functions for oil outflow. This tool was made available to POP&C project partners for use in this project. The development of the tool currently continues with the intention that it will be available commercially after the completion of the project. An integrated methodology has been implemented through existing commercial salvage and naval architectural software packages, plus additional tools developed to provide a probabilistic survivability and oil outflow analysis capability.
Existing, commercially available, salvage response or naval architectural design software (e.g. Hecsalv, NAPA) can be used to model and evaluate individual damage cases including analysis of damage stability, oil outflow and residual hull girder strength after structural damage. Hecsalv has been made available to the 'Pollution prevention and control' (POP&C) project partners for use in this project.
A probabilistic survivability/oil outflow tool to develop damage cases from collision and grounding statistics has been developed. This tool also develops the oil outflow amounts for each damage case, and statistics for all damage cases such as mean outflow, probability of zero outflow, and cumulative distributions functions for oil outflow. This tool was made available to POP&C project partners for use in this project. The development of the tool currently continues with the intention that it will be available commercially after the completion of the project. An integrated methodology has been implemented through existing commercial salvage and naval architectural software packages, plus additional tools developed to provide a probabilistic survivability and oil outflow analysis capability.
Existing, commercially available, salvage response or naval architectural design software (e.g. Hecsalv, NAPA) can be used to model and evaluate individual damage cases including analysis of damage stability, oil outflow and residual hull girder strength after structural damage. Hecsalv has been made available to the 'Pollution prevention and control' (POP&C) project partners for use in this project.
A probabilistic survivability/oil outflow tool to develop damage cases from collision and grounding statistics has been developed. This tool also develops the oil outflow amounts for each damage case, and statistics for all damage cases such as mean outflow, probability of zero outflow, and cumulative distributions functions for oil outflow. This tool was made available to POP&C project partners for use in this project. The development of the tool currently continues with the intention that it will be available commercially after the completion of the project.
The first step of a risk assessment methodology is to carry out a 'Hazard identification and ranking' (HAZID) study. In order to perform the HAZID research programme efficiently, the safety matter under consideration and scope of the study need to be clearly defined. The scope could be limited to a certain ship type, or size, specific accident scenarios, specific operational conditions, typical design and operation concepts, etc.. The 'Pollution prevention and control' (POP&C) project identified the main hazards that lead to a vessel's loss of watertight integrity, causing pollution and environmental damage. Such hazard identification and ranking study can be done by analysing the incident/accident performance of a representative sector of the industry.
The project studied the Aframax class of tankers because of their relatively large market share, past spectacular catastrophic tanker accidents involving Aframax tankers and relatively high number of single hull Aframax tankers which are currently operational and expected to continue operating until they reach the phase-out date.
Mainstream techniques (what-if analysis, what-if/checklist analysis, hazard and operability analysis, failure modes and effects analysis, fault tree (FT) analysis, event tree (ET) analysis and human hazard identification) are used for hazard identification and ranking in the maritime world. These methods were reviewed and a method utilising FT and ET techniques was chosen. A ranking methodology was developed, and three classifications of risk were proposed, addressing the three types of consequences i.e. human safety, property and environmental impact.
Hazards potentially leading to the loss of watertight integrity of the ship were identified, namely collision, contact, grounding, non-accidental structural failure, fire and explosion. These hazards were detailed further by using the risk contribution tree methodology. Combinations of causes leading to the occurrence of these incidents were described according to the FT methodology. The sequences of events following the occurrence of these incidents were described according to the ET methodology.
A rational database of Aframax tankers was set up in the framework of the EU-funded project POP&C to enable the full exploitation of the raw incident data compiled and which was commercially available by Lloyd's Marine Information Service (LMIS). The textual information presented in the incident data were re-analysed by a team of the POP&C project partners and were introduced in the newly-developed database to produce appropriate accident statistics.
On the basis of the incidents highlighted previously and the FTs and ETs that were undertaken, a generic risk model for tankers was developed. Pollution is considered to be a potential consequence following the occurrence of an incident. Because it is impossible to produce a universal risk model covering all aspects relative to safety, it was decided to perform a more general screening of all the possible accident scenarios that can lead to a vessel's loss of watertight integrity.
The most critical accident scenarios were identified. An accident scenario is a specific sequence of events from an initiating event to an undesired consequence, so it starts from one or several basic events of an FT to an end event of an ET. The identification process was achieved by ranking the different scenarios according to their risk level, which is the combination of their likelihood of occurrence and the severity of their consequences. Each scenario is characterised by three risk indexes, one for each type of consequence: human life, property and environment.
The ranking process was split into two steps, the ET analysis and the FT analysis. For the ETs, the identification of the most critical sequences was based on a qualitative assessment made by experts in the maritime field. Three classifications of risk were obtained, one for each type of consequence.
As the top event frequencies were available from the tanker database, it was found sensible to fully quantify the higher levels of the fault FTs; this was achieved by using experts' judgements. A comparison between historical data and experts' elicitation was also performed. Both sources of information have advantages and disadvantages. Historical data are factual information which can not be discussed as they are based on past experience feedback. However it is often difficult, indeed impossible, to piece together the sequence of events of the accident scenario.
The pollution mitigation and control objective of the 'Pollution prevention and control' (POP&C) project was to formulate a pollution-mitigating and control framework capable of covering oil spill incidents/accidents generated from vessels (tankers).
This work started with the formulation of a list of 'Pollution control options' (PCOs) focusing on onboard procedures and. A detailed and complete analysis of the event trees (ETs) created previously within the project and the corresponding scoring procedure held in the brainstorming session was collated.
A descriptive analysis of the ETs as well as a comparative approach of other similar efforts developed within other EC projects was performed. Then, the results of experts' judgments were further exploited through a comprehensive analysis of ETs with regard to the environmental consequences and finally, to the pollution risk. In this analysis, the use of specialised software in order to create rules and decision trees which would form the minimum scenarios (otherwise stated critical events) for the selection of the case studies was considered essential. Finally, a selection of the most critical scenarios per type of accident and the case studies per accident that should be examined were proposed.
The case studies analysed are the following:
- grounding - Braer and Sea Empress accidents,
- collision - Atlantic Empress accident,
- contact - Katja accident,
- non-accidental structural failure - Erika and Prestige accidents,
- fire - Mega Borg accident,
- explosion - ABT summer accident.
The main category of pollution control options were:
-procedures for emergency response (place of refuge),
-tug assistance,
-tanker design and associated regulations,
-systems onboard,
-systems for pollution control and mitigation,
-human factor - training.
Next, efficiency of the identified PCOs was examined. For the scope of the analysis, a methodology was developed which utilises the ETs along with the results of the brainstorming session (experts' judgments), and another set of real ship accidents. Next, the number of related and critical PCOs is determined followed by the most critical to the case study. Finally, the developed scenario from the methodology is presented together with the corresponding experts' scoring.
As part of the following step, the existing post-accident guidelines were assessed and improvement proposals are presented. Moreover, this part of the study focused on the human involvement in post-accident pollution control efforts.
An emergency situation onboard a vessel is any incident that threatens the safety of human life, the safety of the ship, and the marine environment. The international maritime community is continuously putting effort into regulating all necessary actions that should be taken onboard (by the master and the crew), to confront an emergency situation. The first part of the work was dedicated to the identification and presentation of various existing plans, codes and guidelines. In order to achieve this, three different types of methodologies were developed:
1. The operational flow chart (OFC), which is a diagram representing the pattern of actions and procedures taken by the captain, the officers and the crew of an oil carrier as soon as an accident has occurred
2. The hierarchical task analysis (HTA), which is an approach representing an evaluated description of the work onboard the vessel after the accident.
3. The target analysis (TA), which consists of all the necessary sequence of actions/processes that should be adopted in order to achieve a specific predefined target (e.g. avoidance of inclination, or maintaining deck integrity).
In order to assess effectiveness of the 'virtual' decision support tools, five inter-related decision support tools (complementing each other) were identified to support the selected pollution control actions.
The identified generic decision support tools, employed either independently or in tandem with several others were assessed to be useful in reducing the consequences of major accidents, thus reducing the environmental risk associated with Aframax tankers.
Lastly, the potential of the selected control measures have been evaluated. The effectiveness of any PCO is measured by its potential for reducing the severity of the initial incident from a catastrophic (scale 4), to a severe (scale 3), to a significant (scale 2) or most preferred to a minor one (scale 1). The failure in reducing the severity of the initial incident is also recorded.
A risk reduction index was determined by the 'Pollution prevention and control' (POP&C) project for the application of operational measures on the risk of oil spills from tankers. The study began by identifying and assessing risk control options that could avoid accidents leading to oil spills.
Numerous methodologies were studied to determine the critical basic events where risk control options could be applied. Finally, a methodology based on the use of Monte Carlo simulations has been undertaken in order to select the most influential basic events.
A list of critical basic events was determined for different risk components. Since the grounding and collision category of accidents contributed more to the total environmental risk than any other category of accidents, it was concluded that we should focus on the top event types collision and grounding in order to develop risk control options (RCOs).
The following case studies were analysed:
- grounding - Braer and Sea Empress
- collision - Atlantic Empress,
- non-accidental structural failure - Erika and Prestige.
Analysis of the literature considered the subjects of tug assistance, watchkeeping procedures and structural maintenance (double hull tanker 'European maritime safety agency' (EMSA) report). Installation of innovative systems can also be a risk control option in order to assess ship structure and to improve tug assistance.
From all these sources, various types of RCOs have been derived. These RCOs have been categorised into six main types of issues to tackle during a tanker accident:
- procedures for emergency response,
- tug assistance,
- tanker design and associated regulations,
- systems onboard - decision support tool,
- human factor - training,
- others.
The RCOs concerning emergency procedures constitute emergency procedures onboard and their application and the development of coordinated procedures onshore with all the actors of the domain. In particular, the issue of place of refuge, should be envisaged, case by case, with the help of decision-making tools for coastal authorities.
For the grounding type of accident, numerous improvements should be made within the scope of tug assistance (procedures and escort tug schemes). Some RCOs also involve tanker design and in particular, redundancy of steering and propulsion, anchor release systems, design loads calculations for Butterworth covers and improvement in the regulations concerning coating.
A large number of RCOs focused on the use of onboard systems for navigation and the development of a decision support tool helping the crew to anticipate the ship's motions in particular conditions. Navigation aids such as the automatic identification system (AIS), integrated bridge system (IBS) or the expert system for collision avoidance should be used as common practice. The work carried out also pointed out some needs in the domain of the training of crew for navigation (watchkeeping) and for emergency situations in order to reduce the human errors leading to accident.
In order to determine the most feasible and efficient RCOs, a selected number need to be evaluated using simulations. In order to obtain RCOs that could be assessed from an operational point of view, four criteria have been considered which are: operational feasibility, risk reduction efficiency, decision support tool implementation, and simulation ability.
A simulation based decision support tool (DST) was developed which provides a computer based on-line early warning system for grounding avoidance. The tool itself, i.e. the software program, was installed, tested and evaluated at the bridge simulation facility of STC in Rotterdam.
The simulator experiments on prevention scenarios study were based on the following objectives:
- to develop simulator scenarios for a study of the relevancy of DST tools used for the reduction of collisions and groundings with sea-going ships causing marine and coastal area pollution;
- to validate the developed scenarios that will be used to investigate the relevancy of a DST tool with a ship path prediction feature which, should reduce the probability of a grounding in shallow water areas;
- to validate the developed scenario that will be used to investigate the relevancy of AIS for reduction of frequency of collisions between ships at sea.
The proposed scenarios were used to investigate whether DST and AIS could improve the safety of navigation of tankers to reduce the risk of collisions or groundings. Based on the executed runs, the first impression of the navigators was that the DST tool will be able to improve the accuracy of navigation under more critical circumstances.
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