The seaway trade market has expanded in the last years and container ship dimensions are constantly increasing for higher cargo capacity. In the early design stage, main dimensions are usually determined based on an existing ship database from which regression formulas are derived. In the present paper, a database of 260 non-sister container ships built from 1979 to 2022, representing 20% of the world fleet, has been considered to derive and compare different types of regressions. Simple regressions have been developed and compared with equivalent formulations available in literature, proving better approximations of the trends. The study has been further extended by multivariable regressions and forest tree algorithms, which allow the use of more than one independent variable and provide a better fitting compared to simple regressions. Forest tree regressions return the highest values of fitting coefficients, but the technique is not of easy application due to the absence of mathematical expressions. The main contribution is the updated set of simple and multivariable regression formulas which have a higher goodness of fit than previous works and can be easily employed by designers in the early design stage and in multi-attribute design procedures.

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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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The prediction of the statutory attained subdivision index is a challenging issue for the initial design of ships due to the design freedom offered by a probabilistic damage stability assessment. To this end, optimisation techniques integrated with a parametric model of the internal layout may generate a preliminary subdivision design, fulfilling damage stability regulations and cargo volume requirements. The present study explores using a multi-objective constrained optimisation algorithm coupled with a parametric model of a single hold cargo vessel, first investigating two design goal alternatives and secondly performing a global sensitivity analysis on the design variables for the most promising solution. The adoption, in parallel, of state-of-the-art practices shows the validity of the obtained solutions and the time benefits for designers. Nonetheless, the non-linear nature of probabilistic damage stability does not allow for clearly identifying the most impactful parameters on the attained survivability index.

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The Dynamic Positioning system allows a vessel to keep a precise position and heading during stationing operations in a rough sea by using onboard actuators only. During the design phase, it is mandatory to identify the capability of the system actuators to counteract the environmental forces. Conventional predictions are limited to the estimation of a maximum sustainable wind speed on predefined encounter angles by estimating the corresponding wave parameters with questionable standard deterministic correlations. The proposed approach aims at determining the dynamic positioning performances by using site-specific long-term environmental conditions which are modelled with joint distributions of wind and wave parameters. To this end, the operability of the dynamic positioning system is evaluated as a non-deterministic multidimensional Monte Carlo integration process, based on the sampling of environmental joint distributions. For each environmental condition, a quasi-static dynamic positioning analysis is performed solving the equilibrium between external forces and the vessel's actuators through a non-linear thrust allocation algorithm. The proposed methodology is applied to a reference offshore ship in five different operative geographic areas, highlighting the suitability of the calculation methodology for site-specific operability predictions.

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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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Real-time assessment of flooding risk associated with the collision between two ships, requires a fast estimation of damage dimensions and associated survivability. The state-of-the-art frameworks for risk assessment on passenger ships do not consider a direct evaluation of damages through crash simulations but refer to probabilistic considerations, modelling damage characteristics according to statutory marginal distributions of damage breaches too old to be any longer relevant. In any case, such an approach is not possible for the real-time risk assessment process developed in project FLARE, aimed at promoting the employment of first-principles tools for risk evaluation. In this spirit, the present work investigates the possibility of developing a database-oriented damage breach model, which employs direct crash analyses with the super-element code SHARP. However, the sole usage of crash simulations is not suitable for real-time applications. Therefore, starting from the collision simulation database, surrogate models have to be derived for real-time application. In this specific case, three different strategies have been used for the models creation namely: multiple linear regressions, neural networks and decision trees. Here, the strategy to build the database and application on a reference passenger ship is described, highlighting the differences in accuracy and calculation time between the proposed surrogate models.

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The importance of comfort during transfer and stationing becomes a key performance parameter for large yacht design, on the same level as propulsive issues. Such a matter extends questions in terms of form and service demand to the motion behaviour of the unit in waves. Relevant studies refer to outdated hull forms not specific to modern large yachts. In this study, five hull forms with different bow concepts represent the most common design solutions for yachts at constant draught and displacement. The preliminary ranking on the effect of alternative bows on comfort requires the definition of internationally accepted comfort standards. Here, the AWI 22834 guidelines for large yachts provide the service and environmental conditions and criteria for the comfort analysis, being the only reference specific to yachts. The calculations employ a strip-theory-based numerical model to provide results of easy understanding for designers during the early design stage. The obtained ranking among the design solutions on a reference large yacht favours the option nested with a bulb, contradicting the expectations in favour of a vertical bow concept. The discussion and conclusions provide a way forward for additional analyses and investigations aimed at proposing suitable multicriterial design guidelines for large yachts. However, the results also show the unsuitability of AWI environmental and encounter conditions for hull form ranking. @en

The focus on digitalisation in manufacturing is spreading to other industry fields, including large and complex objects like ships. Such interest introduces the concept of Digital Twins in supporting designers and operators through the whole ship-life cycle. However, the term Digital Twin is typically abused in the shipping industry, many times erroneously referring to any virtual version of a model-based system as a Digital Twin of the ship. The mutual data exchange between the physical and virtual environment, which is the basis of a true Digital Twin, is mostly missing, confusing a virtual model with a sophisticated living virtual environment. Few reviews are available in the literature for Digital Twins on ships. This systematic review proposes the identification of weaknesses and correlations between current Digital Twin applications in the maritime industry and other industry fields. Furthermore, the methodology applied here may be repeated in future studies to provide a fair and objective overview of the research advancements in the topic. The study highlighted how literature scarcely addresses the design and decommissioning phases, indicating that research should focus on these topics, especially concerning the design of future ships.

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The in-force probabilistic framework for passenger ship survivability assessment covers collision hazards. The framework primarily pertains to a static approach. Nonetheless, more complex dynamic analyses usually employ the same damage definitions, adding besides the breach characteristics, the environmental condition selection or, more precisely, the irregular wave environment necessary to simulate the damage scenarios. The traditional dynamic approaches to survivability consider only the significant wave height sampled from statistical formulations, with the wave period deriving from a constant steepness assumption. However, wave height and period influence ship dynamics in waves differently, especially concerning survivability after damage. Therefore, aiming at a direct assessment of ship survivability and the probability of loss of lives determination in realistic operational scenarios, it is essential to properly study the influence of combined variations of wave height and periods and their occurrence. The present study proposes a methodology for dynamic simulations in site-specific conditions derived from the Global Wave Statistics. The study documents the process in two critical collision damages for a reference passenger ship, using wave height and period combinations typical of the main sea areas of interest for passenger ships and performing a sensitivity analysis on the simulations needed to evaluate survivability. This enhanced analysis allows identifying the limiting environmental conditions for the critical damage cases, including the effect of heading variations, determining the ship's survivability to specific damage in an operational area.

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The increasing demand for offshore operations in deep water implies the necessity to predict station-keeping ability of offshore vessels since the early stages of design. To this end, besides developing sufficiently fast and accurate methodologies for the equilibrium resolution of the forces acting on the ship, it is of utmost importance to estimate, in a reliable way, the external forces acting on the vessel. This work focuses on the current loads, aiming at developing a model for fast current load prediction based on high-fidelity Computational Fluid Dynamics (CFD) computations. Selecting the drill-ships as reference vessel-type for the study, starting from the actual fleet operating worldwide, a systematic series of hulls has been generated varying the main hull-form parameters inside the database, according to a Box-Behnken scheme. CFD calculations based on RANS equations have been performed on the whole ship set, for a set of incidence angle varying from 0 to 180 degrees considering the hull symmetric. As numerical analyses are not suitable for fast calculations the results on the systematic series have been used as input for developing a surrogate model based on Multiple Linear Regressions (MLR). The method allows for scaling the results as a function of the Reynolds number, allowing for general and flexible applicability among different vessel dimensions. The results obtained with the developed model are compared with the conventional current loads estimation methods, and the obtained results are compared on the capability plot, highlighting the higher reliability of the proposed model for early-stage predictions.

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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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Determining Dynamic Positioning capability for an offshore vessel is mandatory to identify the environmental forces the system can counteract, together with the operability in a specific operational area of interest. Conventional predictions evaluate the capability as a maximum sustainable wind speed at a predefined encounter angle for a given wind–wave correlation, not reflecting the effective wind and waves occurrence at the site. In this respect, a step forward is provided by the scatter diagram approach, allowing the evaluation of operability in a specific sea area, using a simplified method to predict wind speed from wave parameters. Here, using known wind–waves joint distributions for the long-term environmental conditions further improves the scatter diagram approach, assessing the operability of a Dynamic Positioning system through a Quasi-Monte Carlo sampling of the joint distribution. Analysing the results of the Quasi-Monte Carlo process, it is possible to obtain a site-specific capability plot, allowing the identification of critical wind speeds in a way that is familiar to operators in the offshore industry. The application of this novel method in the case of quasi-static calculations both to a reference supply vessel and a pipe-lay vessel shows the flexibility of the proposed approach for site-specific Dynamic Positioning capability predictions.@en

Preliminary prediction of escort tug capability aims to identify the maximum steering and braking forces the tug could deliver during operations at sea. To this end, the adoption of a steady-state equilibrium approximation ensures attaining a quick and enough accurate results for the initial design stage. Diverse techniques are suitable to resolve the equilibrium, with different simplification levels and related limitations. In this study, a method based on a nonlinear thrust allocation algorithm is improved, including propulsors interactions. Moreover, the addition of the transversal equilibrium modelling of the tug allows evaluating the compliancy with stability and safety Regulations for escort class. The coupling between enhanced equilibrium resolution and a simplified approach to estimate the hydrodynamic forces results in a flexible prediction method for tug escort capability, which is requiring few inputs, without excluding the possibility to use higher fidelity hydrodynamic loads. The calculation framework, implemented with different levels of confidence for hydrodynamic loads, is tested on different tug types, highlighting its flexibility compared to more traditional and widely accepted approaches for the initial design stage.

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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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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

The current damage stability regulatory framework for passenger and dry cargo ships allows addressing vessel survivability after flooding due to collisions with probabilistic requirements. This methodology also applies to other hazards responsible for the flooding of a ship such as bottom and side groundings. Traditionally, the application of Monte Carlo sampling of pertinent distributions allows for assessing ship survivability. Such a method introduces randomness in the process, leading to a dispersion of the attained survivability index within multiple sets of generated damages. The present work investigates sampling methods alternative to Monte Carlo, based on Latin Hypercube and Randomised Quasi-Monte Carlo processes. The sampling methods application for collisions, side and bottom groundings on a reference barge available in the literature for benchmark purposes shows that the Randomised Quasi-Monte Carlo method based on multidimensional Sobol sequences grants lower dispersion of the final survivability index data within samples of equivalent size. Finally, the application on a sample cruise ship of Monte Carlo and Randomised Quasi-Monte Carlo methods highlights the possibility to reduce the number of damage breaches necessary to evaluate the survivability index within an engineering confidence interval, thus improving accuracy and efficiency in the amplification of probabilistic damage stability methods by the industry.

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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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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 survivability of a passenger ship after an accident is assessed by a probabilistic framework covering hazards like collisions and groundings. Such assessments are a key determinant for the internal ship arrangement and layout, affecting ship design and operation. The framework pertains to static assessment, but it is common to use the same damage definitions for dynamic calculations. In the latter case, besides the breach characteristics, the environmental condition selection is of paramount importance. In the specific, irregular waves modelling, it is necessary to simulate the damage scenarios. In the common dynamic approaches to survivability, attention is paid to the significant wave height of the calculation, considering the wave period constant. The wave height is not always reflecting real scenarios but is derived from statistics of collisions (GOALDS project). However, wave height and period influence ship dynamic in waves (in intact or damaged conditions), impacting survivability after damage. Aiming at a direct assessment of ship survivability and the probability of loss of lives determination in realistic operational scenarios, it is essential to properly study the influence of combined variations of wave height and periods and their occurrence. In the present study, dynamic simulations are carried out in site-specific conditions derived from the Global Wave Statistics. Critical cases are derived from conventional survivability analyses on a sample passenger ship. The same cases are then analysed using wave height and period combinations typical of the main sea areas of interest for passenger ships. This enhanced analysis allows to clearly identify the limiting environmental conditions for the critical damage cases, evaluating the effective survivability of the ship to a specific damage in an operational area.

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