The traditional way of assessing the operational risk of passenger ships is based on the concept of susceptibility and vulnerability to an accident. Such an approach is mainly used to study the possible risk in given operational scenarios, adopting simplified quasi-static methods to assess the vulnerability of the vessel and using empirical definitions for the damage breach modelling. These methods are not employing first-principles methods for the risk evaluation and are not suitable for the development of onboard real-time risk assessment. To this end, developments in the EU-founded project FLARE led to a multi-level risk assessment framework based on first principle methods, that can be applied as a basis for an onboard risk assessment in real-time. The framework for real-time assessment is based on the development of databases for damage locations and dimensions and survivability. Here, the development of a suitable database of damages is discussed, concerning the employment of direct crash simulations with the software SHARP, aiming at developing a database of collisions suitable for a general operational scenario. The resulting database can be used as a data source for the development of a surrogate model for fast application in real time. This paper addresses the application of the process to a reference cruise vessel.

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Theory and application of damage stability followed over the years two dissociated paths: static assessments and dynamic simulations. The first approach, being easy to apply and understand, has been preferred by ship designers and regulators; the second, more advanced and first-principle oriented, has been mainly reserved for research or high-level consultancy, especially for passenger ships. Nowadays, the availability of numerical flooding simulation tools across the scientific community and calculation power in the industry allows for a possible definitive transition of damage stability assessment towards direct numerical analyses. However, research should softly drive designers towards more advanced processes via a suitable didascalic calculation framework. The multi-level approach pursued in project FLARE is an example of such a transition from static to dynamic damage stability assessment. The present work initially carefully reviews the probabilistic concept of damage stability, critically comparing the prescriptive statistical methods with direct ones and providing insights and guidance on how researchers and designers can reconcile with the original implicit assumption of the probabilistic approach. Secondly, the development of the multi-level framework highlights incongruences concerning modelling of damages between static and dynamic assessments, disfavouring the comprehension of dynamic results to designers. Two detailed examples highlight the differences in dynamic simulation results between different damage breach modelling, leading to completely different flooding paths for the same damage case. Finally, the paper indicates how a compromise between academic approach and application could help designers to start their transition towards direct numerical damage stability analyses.

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Flooding risk identification is a task always treated within a very narrow scope between the life-cycle of a passenger ship. Therefore, different approaches and methods are available for design, operational or onboard applications. Furthermore, the models employed and proposed solutions use simplified methods based on empirical or probabilistic concepts. One of the aims of the EC-founded project FLARE was to promote the use of first principle methods throughout the whole vessel life-cycle, from the design phase up to the onboard risk management. To this end, this work presents the challenges and potential applicability of a real-time flooding risk evaluation methodology for ship-to-ship collisions, based on first-principles calculations. The possibility to perform direct calculations for survivability allows us to define a multi-level approach to flooding risk, separating Level-1 predictions, purely based on semi-empirical models and databases, from Level-2 predictions based on the concept of Potential Loss of Life (PLL). Here, besides a description of the multi-level risk assessment based on PLL, the different tasks of design and operational phases are addressed. Such issues are then linked to the real-time flooding risk evaluation for onboard applications, potentially working for different hazard types but conceptualised for the case of ship-to-ship collisions. The developed method applied to an arbitrary set of models, shows that the approach and tools employed for creating the framework are suitable for a real-time calculation of flooding risk.

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In naval architecture, the standard way adopted to reduce the risk of potential loss of life for passenger ships after an accident is via regulations. In case of flooding, this explicitly implies the introduction of fixed watertight bulkheads, permanently modifying the internal ship’s layout. Damage stability regulations constantly aim at higher safety standards; therefore, the layout reconfiguration of an existing vessel may be essential to meet new requirements, leading to higher costs for retrofitting. Furthermore, increasing fragmentation of the internal layout has a physical limit, ne-glecting the possibility to elevate standards above a particular upper limit. In this view, innovative solutions give the chance to exceed such a limit. The present work describes the advantages of high-expansion foam application for passive and active protection from flooding events. The possibility to have a material granting sufficient water tightness allows installing fixed or deployable barriers that increase the safety level of the ship. Here, besides the description of the foam characteristics, the application on a reference passenger ship highlights the advantages of passive and active foam barriers to limit flooding and drastically reduce the risk of loss of lives. The changes in the limiting stability margins required by regulations and the analysis of dynamic flooding simulations for spe-cific damage cases demonstrate the benefits of foam installation onboard passenger ships as a risk control option.

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A more contemporary damaged stability assessment of a passenger ship can be addressed with a non-zonal approach, assessing multiple damage types and environmental conditions and employing dynamic analysis for ship survivability. This direct method necessitates the generation and simulation of many damage scenarios. However, the probabilistic models for damage characteristics describe many damages that are not critical for ship survivability. To restrict the number of damage scenarios, hence calculation time, designers currently apply empirical rules, such as critical damages are only above two compartments, considering that damage stability regulations currently in force to ensure survivability levels beyond this damage extent. However, a rigorous approach is lacking. The present work explores the use of more scientific methods as damage filters. The first method uses preliminary static calculations. The second uses the energy absorbed by the ship during an impact, and the third is suitable for a purely dynamic approach. The paper critically compares the three methodologies on two sample passenger ships for collision damages, showing their respective advantages and disadvantages.@en

Against the background of using the Index of Subdivision as a reference to address the safety level of ships when damaged, following primarily collision incidents, the EC-funded FLARE project is making inroads towards a direct assessment of flooding risk, which is ship, operating environment, and accident-type specific by addressing all the underlying elements, using a two-level approach; level 1 being semi-empirical with risk models informed through a newly composed accident database and level 2 with flooding risk, in the form of Potential Loss of Life, calculated from first principles, using time-domain flooding simulation tools and evacuation analyses in pertinent emergencies. In addition to addressing all accident types and modes of loss, the FLARE framework and methodology target active and passive measures of risk prevention and control, hence with application potential to both newbuildings and existing ships as well as facilitate real-time flooding risk evaluation for risk monitoring and effective control in emergencies. A key objective of the FLARE project is to provide the technical basis and a proposal for the revision of relevant IMO regulations towards a risk-based approach to contain and control flooding emergencies. The paper provides a complete example of one cruise ship and one RoPax where levels 1 and 2 of flooding risk evaluation are presented and discussed, and a summary of results for a further 8 sample ships from Project FLARE, leading to conclusions on the progress made and recommendations for the way forward.

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The damaged stability assessment for a passenger ship is a process requiring the simulation of multiple damage scenarios. Nevertheless, the stochastic nature of the damage stability framework requires the analysis of a statistically significant number of cases. On the other hand, the probability density functions used to estimate the possible damage dimensions and locations along the ship generate many scenarios that are not critical for the ship's survivability, especially for large passenger ships. It is standard to apply empirical rules to restrict the number of damage scenarios, such as critical damages is only above two compartments, considering that damage stability regulations currently in force ensure survivability levels beyond this extent of breaches. However, a rigorous approach is lacking. To this end, in the present work, it is proposed to use more scientific-based methods to identify critical damages. This paper presents three original approaches developed in the context of a multi-level damage stability assessment. The first method relies on preliminary static calculations, the second on the energy absorbed by the ship during an impact, and the third on a purely dynamic approach. Here, the methods are critically compared on two sample passenger ships for collision damages, showing their respective advantages and disadvantages.

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The paper complements an earlier publication by the authors addressing the probability of survival in the IMO framework for damage stability assessment, the s-factor. The focus here is on the probability of occurrence of a certain damage scenario (breach), conditional on its dimensions and location (centre and port or starboard side), the p-factor. Pertinent assumptions and limitations are explained, following its evolution for specific application to passenger ships. Attempts to provide analytical descriptions of the damage breach distributions as tetrahedra shapes positioned along the ship length whilst accounting for changes in ship geometry, structural arrangements, and subdivision for consumption by the wider profession has led to misconceptions and misunderstandings of what exactly the p-factor is in the context of probabilistic damage stability calculations. This is evidenced by the fact that the same original damage breach distributions, derived in Project HARDER, based on largely cargo ships with the age spread over the last three decades of the previous century, are still being used today for all ship types, including modern passenger ships. Filling this gap, a new database for passenger ships developed in the EC-funded Project FLARE, is briefly presented, leading to new damage breach distributions specifically for passenger ships. It is believed that this paper will throw considerable light in enhancing understanding on the p-factor, which has been cluttered with unnecessary complexity from the outset.

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Development of damage stability as a scientific subject, specifically in damage ship hydrodynamics and, generally, flooding risk assessment, has evolved primarily by inquisitive academics with support by people with vision and passion towards maritime safety enhancement from industry and Government, the latter in the wake of serious accidents. Notwithstanding this, the subject has seen remarkable development in a short period of time in terms of understanding process, and developing methods and tools for practical implementation of such developments. The stage has now been reached where large-scale EC and industry-funded projects are bringing all requisite knowledge and experience together towards implementation by end users with the view to institutionalizing such developments. The paper critically traces and presents key developments starting from basic concepts to a complete framework for performing numerical simulations of ship survivability in operational conditions in the seaway, leading to flooding risk assessment with application potential for new and existing ships with focus on the design phase but with operation potential in ship operation, the latter involving emergencies.

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Ships are designed based on three basic objectives pertaining to ship performance, functionally and safety, all dictated by external shape, internal layout, deadweight, payload, permeable volume, and their distributions. All, except for one, are calculated to extremely small tolerances and are subjected to rules and regulations that have been evolving for thousands of years. The exception is “permeable volume”, (the internal free space in the ship hull and superstructure available for flooding), which is of the same magnitude as weight and buoyancy. Over the years, some generalised approximations have been adopted for principal ship spaces without differentiating between ship types, leading to gross approximations when calculating ship damage stability. In the latter case, the amount and distribution of residual permeable volume (together with buoyancy and weight), dictate whether a ship may sink because of inadequate buoyancy or capsize due to loss of stability. Yet, whilst all pertinent parameters are calculated to extreme accuracy, permeable volume and its distribution is calculated with naïve approximation. To demonstrate the impact of such approximations several passenger ships are considered in the paper, covering the whole range of ships in operation, and a sensitivity analysis is undertaking addressing the main ship spaces and their contribution to permeable volume, offering unique insight on the key influence of permeability on ship damage stability. Building on this, the impact of permeability as a key design option to affect life-cycle stability management is elaborated and demonstrated, leading to conclusions and recommendations.

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Stability has been a primary focus of the maritime industry and of immense interest to the IMO from the outset. Despite several attempts to resolve stability-related issues, the problem of stability remains one that has yet to be resolved. Reasons for this, range from the complexity of the problem itself to misconceptions in its very nature, particularly concerning compromised conditions of the ship in question. More specifically, whilst stability of ships is an extremely interesting scientific problem and a determining factor in ship design, the impact on the operation of passenger ships, a matter of crucial importance from the dual point of view of safety and economics, has hardly ever received the attention it deserves. Currently, intact stability and damage stability share the same stage from a regulatory perspective and, consequently, they have equal impact on design and operation-related decisions, an example of which is the use of combined intact and damage stability GM limit curves (e.g. IACS Rec 110 Rev1). However, in line with goal-based regulations and standards, design and operational decisions should be risk-informed in which case, matters relating to damage stability are of higher concern, simply by virtue of the fact that damage stability is by far the greater risk contributor. In fact, for passenger ships (>500GT), the level of risk associated with intact stability is indiscernible in contrast to that of damage stability. More importantly, in the operational loading conditions of such vessels, damage stability is a more dominant constraint. Hence, such ships are designed based on damage stability considerations alone. However, since life-cycle risk management is still an active research subject, stability management is being addressed somewhat haphazardly by allowing for design GM margins, drawing from experience on the average deterioration of GM over the life-cycle of passenger ships. This is typically 1% to 2% per year on average, which leaves roughly 50% of ships on the wrong side of this averaging process and this, in turn, limits operation substantially with severe economic impact. This paper delves in this direction by drawing on current ship design and operational practice and presents an innovation with application to a large cruise ship to demonstrate how life-cycle damage stability management could be tackled in a structured and cost-effective manner.

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