Polar diagrams, which map wind speed and angle to boat speed, are fundamental tools for sailing performance analysis, race preparation, and coaching. Yet data-driven polar models typically produce point predictions without principled uncertainty, leaving coaches unable to distinguish genuine crew differences from noise or to set statistically grounded training targets. Furthermore, Olympic classes lack manufacturer-supplied polars, so sailors must rely on on-water testing and racing to benchmark against competitors. This paper presents the Sailing Performance Additive Model (SPAM), a 28-parameter model that addresses both prediction quality and uncertainty quantification through a basis design informed by sailing physics. SPAM combines physics-motivated basis functions, including power-law wind scaling, Fourier angular harmonics, and their interactions, fitted via Ridge regression. This architecture admits an exact Bayesian interpretation, yielding closed-form prediction intervals without sampling or simulation. A residual-based noise surface separates model uncertainty from inherent performance variability, making SPAM a coherent probabilistic model. Evaluated on GNSS tracking data from 21 Olympic Nacra 17 crews across 9 international regattas including the Paris 2024 Olympic Games, SPAM captures 95% of learnable variance and achieves 15–18% lower prediction error than Random Forest and GAM baselines when extrapolating to held-out regattas. Practical applications are demonstrated: condition-dependent confidence bands, percentile polars that distinguish a crew’s best achievable performance from their average day on the water, and crew comparison with statistically grounded confidence intervals.

This paper discusses the impact of scaling effects in the performance of a standalone wing sail, comparing experiments and numerical simulations. The experimental data of a standalone wing sail with a NACA0015 section, tested in the R.J. Mitchell wind tunnel at the University of Southampton, are compared with wind tunnel tests run at KTH Royal Institute of Technology, where the L2000 wind tunnel and wing sail had a smaller scale, and with Computational Fluid Dynamics simulations of three different cases. For the numerical simulations, first the model scale Southampton wind tunnel was simulated. Then, keeping the same scale, the wind tunnel domain was substituted with a larger domain to simulate an open-field condition, and analyse the presence of blockage effects. Finally, full-scale simulations were achieved keeping the same scale of the model scale open-field simulations, and reaching the full-scale Reynolds number by varying the viscosity of the fluid. The flow in the numerical simulations is modelled with the RANS equations and the k − ω SST turbulence model, knowing about its limitations in simulating stall conditions, but judged to be satisfactory for a preliminary study about scale effects. The range of model scale Reynolds numbers covered by both experimental campaigns spans from 2.2x105 to 6.7x105, while the full-scale Reynolds number is equal to 7.9x106, covering a range representative of most wind propulsion technologies. The main conclusions are that the simulations capture well the shape of the lift curve up to an angle before stall, after which the simulations diverge from the experiments. In full-scale, higher lift coefficients are reached, and the lift curve shows a different behaviour than in model scale, with a longer linear region and a more abrupt stall. © 2025 CSYS. All rights reserved.

Venue-specific training has, over the years, proven to be a key asset for sailing teams performing at major championships and at the Olympics. A comprehensive understanding of the environmental features and possible weather scenarios in an outdoor sport like sailing can provide athletes with a significant strategic advantage. At the same time, GPS tracking is becoming a readily available technology that athletes use both in training and during races to analyse their own and their competitor’s performance. This work couples environmental and meteorological data with GPS tracks for Olympic sailing classes, linking weather features with strategic decisions on the race track. We propose a greedy algorithm to search for an optimal route based on weather forecasts to present the best strategy prior to the race. Our results show the potential of this approach to provide valuable decision support for athletes in Olympic sailing competitions, demonstrated for the 470 Olympic class.

Computational Fluid Dynamics (CFD) simulations to predict forces from a Wind Propulsion Unit (WPU) on a ship hull are carried out to better understand the forces dependency on wind speed and angle. Three different Atmospheric Boundary Layer (ABL) stratifications, nominally unstable, neutral, and stable, are studied in a CFD environment to better understand how to reproduce these velocity profiles numerically and how much is their impact on the performance of a general ship’s hull equipped with a Flettner rotor. A series of 2D and 3D simulations with an empty domain are run to tune some numerical settings for a correct representation of the ABL. Simulations with a simplified hull and a Fletter rotor are run to purely analyse the differences between the profiles and their effects on a reproduceable geometry. The three different ABL profiles are tested for four different wind angles, producing an overview of the dependency of rotor and ship performance on wind speed profiles, wind angles and hull interaction. A clear impact of the wind profiles and the wind angle on the ship hull is visible on the rotor lift and drag coefficients, while in terms of ship performance, described by the ratio of the thrust and side force coefficients, the impact is limited

The NACRA 17 is a small foiling catamaran that is lifted out of the water by two asymmetric z-foils and two rudder elevators. This paper investigates how foil deflection affects not only foil performance but overall boat behaviour using a numerical Fluid Structure Interaction (FSI) model. The deformations are solved with a solid model based on the Finite Element Method (FEM) and the flow is solved with a Reynolds Average Navier-Stokes (RANS) based Finite Volume Model (FVM). The models are strongly coupled to allow dynamic FSI simulations. The numerical model is validated by comparing it to an experimental campaign conducted at the RISE SSPA Maritime Center in Sweden.Validation shows reasonable agreement, but the model can only be considered validated for some rake angles. The large deformation of the foils is found to have a profound effect on the performance of the foils and therefore of the overall catamaran. Turbulence transition and boat speed are found to affect foil forces and, in turn, deformation. Dynamic response of the foils during boat motion as exposed to waves is investigated and finally the full boat hydrodynamic is simulated by including both foils and the rudders in various scenarios.

Modern wind propulsion systems on ocean-going cargo vessels require automated trimming. Rigid wingsail designs often incorporate more than one degree of freedom enabling to trim for optimal performance in all sailing conditions. A profound understanding of the aerodynamic behavior is the basis for any trimming strategy. The region around stall is of particular importance as this is where the largest lift but also potential hysteresis effects are expected. In the present research, a two-element wingsail (main wing and flap) was tested in wind tunnel experiments investigating the two available degrees of freedom: the orientation of the main wing to the inflow and the deflection of the flap. Aerodynamic loads were measured in dynamic actuation sequences over both degrees of freedom capturing stall and reattachment. The consistent data reveals two stall stages. In the region between the first and the second stall, when changing the direction of rotation, the flow is found to be reversible. The hysteresis loop is in this case smaller and reattachment occurs at larger angles compared to when both stall stages occur. This smaller hysteresis loop could be exploited in trimming. The second stall stage, however, is identified as detrimental both in the forces and the amount of required actuation to allow the flow to reattach. A considerate flap trim, i.e. the adjustment of the wingsail curvature, is suggested to avoid the second stall.

Match racing starts in sailing are strategically complex and of great importance for the outcome of a race. With the return of the America's Cup to upwind starts and the World Match Racing Tour attracting young and development sailors, the tactical skills necessary to master the starts could be trained and learned by means of computer simulations to assess a large range of approaches to the starting box. This project used game theory to model the start of a match race, intending to develop and study strategies using Monte-Carlo tree search to estimate the utility of a player's potential moves throughout a race. Strategies that utilised the utility estimated in different ways were defined and tested against each other through means of simulation and with an expert advice on match racing start strategy from a sailor's perspective. The results show that the strategies that put greater emphasis on what the opponent might do, perform better than those that did not. It is concluded that Monte-Carlo tree search can provide a basis for decision making in match races and that it has potential for further use. 

Hydrofoils are a current hot topic in the marine industry both in high performance sailing and in new passenger transport systems in conjunction with electric propulsion. In the sailing community, the largest impact is seen from the America’s cup, where boats are sailed at more than 50 knots (over 100 km/h) with 100% “flying” time. Hydrofoils are also becoming popular in the Olympics, as in the 2024 Olympic games 5 gold medals will be decided on foiling boats/boards. The reason for the increasing popularity of hydrofoils and foiling boats is the recent advances in composite materials, especially in their strength to stiffness ratio. In general, hydrofoils have a very small wetted surface area compared to the wetted surface area of the hull. Therefore, after “take-off” speed, the wetted surface area of the hull, and consequently the resistance of the boat, is reduced considerably. The larger the weight of the boat and crew and the higher the speeds, the greater the loads on the hydrofoils will be. The current research investigates the interaction effects between the fluid and structure of the ZP00682 NACRA 17 Z-foil. The study is carried out both experimentally, in SSPA’s cavitation tunnel, and numerically using a fully coupled viscous solver with a structural analysis tool. The experimental methodology has been used to validate the numerical tools, which in turn are used to reverse engineer the material properties and the internal stiffness of the NACRA 17 foil. The experimental flow speed has been chosen to represent realistic foiling speeds found in the NACRA 17 class, namely 5, 7, and 9 m/s. The forces and the deflection of the Z-foil are investigated, showing a maximum deflection corresponding to 24% of the immersed span. Finally, the effects of leeway and rake angles on the bending properties of the Z-foil are investigated to assess the influence of different angles in sailing strategies, showing that a differential rake set-up might be preferred in search for minimum drag. © 2022 by the authors. 

The effects of multiple wings interacting and the change in efficiency due to those effects as well as optimal sheeting angles are becoming an important area of study with the advent of wind-propelled ships for goods transport. This research presents a first analysis of wind tunnel tests carried out at the University of Southampton R.J. Mitchell wind tunnel where three wings are subject to turbulent flow with Reynolds number in excess of 1 million. A range of possible variations of ship heading and apparent wind angles are tested taking into consideration the blockage effects and the geometrical characteristics of the working section. The forces and moments are captured on each individual wing as well as in the overall wind tunnel balance with 6-components dynamometers. Furthermore, pressure sensors and PIV data are recorded during the tests to provide the experimental campaign with results that can validate both qualitatively and quantitatively the numerical tools developed to aid the design stage of wind propelled vessels. 

The Tokyo 2020 Olympic Sailing Competitions were held in Enoshima Bay between the 25th of July and the 4th of August 2021. The climatological and the strategical analysis of the race area for the Swedish Sailing Team was developed in the three years prior to the Olympics (Masino et al., 2021). The result of the three years’ research was a tool named ”Call Book” that provides strategical rules for sailors and coaches both in terms of expected ranges of wind speed and direction and also in terms of trends with explanations for each identified weather pattern. The support team was working not only on the forecast but also on the specific analysis of the weather data in the race areas as measured on the water by the Olympics organizing authorities and monitored through the SAP Analytics website (SAP Sailing Analytics, 2021). Two race areas are herein taken into consideration, namely Enoshima and Zushi, where the Swedish Team athletes sailed most of the races. A statistical meta-analysis on the comparison between the forecast issued using the ”Call Book” and measured data on the race areas is carried out, investigating the specific outcome of the strategy of the races with the forecasted meteorological data.