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 Relevant studies refer to outdated hull forms not specific to modern large yachts.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 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 some specific environmentally protected areas, conventional mooring systems cannot be used by large yachts for stationing at anchor and therefore, the adoption of a dynamic positioning system is required. It becomes then necessary to evaluate the station keeping capabilities of a yacht since the early-design stage. Adopting a quasi-static approach, it is possible to perform a standard capability analysis, as commonly done for the offshore industry, obtaining a capability plot as output. However, capability plots are referring to specific wind-wave correlation that are not covering all the possible wave combinations present in a sea area. Here, it is proposed to use a scatter diagram approach for the dynamic positioning analysis of a large yacht, considering the specific sea areas where the yacht shall operate, in order to figure out the downtime period of the DP system per each sea area. The proposed method can be coupled with traditional ship motions analysis, leading to a combination between comfort assessment and DP predictions. In the present work, use has been made of a traditional displacement yacht 72 m long, comparing five different DP system configurations and evaluating an enhanced comfort ranking combining ISO AWI-22834 guidelines for large yachts with ISO AWI-22822 DP analysis.

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