Probabilistic Added Wave Resistance Predictions for Design of RoPax Ferries

Sammanfattning: This thesis investigates reasons for significant uncertainties in added wave resistance predictionsand how wave conditions can potentially affect the design of RoPax ferries. The objectiveis to find a suitable prediction method of added wave resistance for the RoPax ferry designapplication. Furthermore, the wave environment on the route strongly influences this delicateand complex phenomenon. Thus, the emphasis is to understand the added wave resistancethrough a case study with a probabilistic wave environment.The fast transition into decarbonization and regulations regarding energy-efficient ship designhave ramped up the awareness of the influence of seaways. For lower speeds, the addedresistance becomes a more significant part of total resistance, with concerns regarding minimumpropulsion power and safe maneuvering in adverse sea conditions. Consequently, the demandhas rocketed for profound insight and accurate prediction methods of added wave resistance. Inaddition, with new larger ships, added wave resistance domain for short waves becomes essentialand an additional challenge regarding predictions. Nevertheless, added wave resistancepredictions are complex and contain many pitfalls, so accurate estimations of the ship’s addedwave resistance response and wave environment are crucial. In addition, added wave resistanceis very ship-specific, and published research for RoPax ferries is rare.Due to significant uncertainties for general numerical methods, the study investigates a new(modified NTUA) semi-empirical method refined for ships with a large beam-to-draft ratio.In addition, a realistic wave environment is included by selecting relevant wave spectra forconditions on the route.The study shows that significant variances of added wave resistance predictions arise fromselecting prediction methods beyond the range of applicability and rough assumptions of waveconditions and spectra. The case study discovered that errors might also be introduced bythe classification society definitions, which gives reasons to rethink the applied definition of"average BF 8" wave conditions for Safe Return to Port (SRtP) assessments. This can causea false illusion of the ship’s performance and safety in waves. Only the misjudgment ofthe most critical peak period resulted in a rough underestimation (> 40%) of mean addedwave resistance. The error corresponded to 215% of the still water resistance for the SRtPassessment. In addition, the nature of added wave resistance is very ship specific. Therefore, theauthor emphasizes caution when selecting the prediction method, especially for semi-empiricalmethods. Despite the first promising glance of the applied semi-empirical method, it appearsthat the ship database correlates poorly for RoPax ferries. Reliability for the method is weak forshort waves, with a tendency to large overestimations. The lack of references of RoPax vesselsfor validations, accident statics in adverse sea conditions and recent insight into nonlinear effectsrequest further research on added wave resistance for modern hull shapes.