Stability Criteria for Sailing Vessels

What do you know about sailing yacht stability? Which are the peculiarities of the stability of a sailing yacht? Is there any supposition different from those applied in conventional ships? If you have to verify the stability of your yacht, would you be sure of which criteria you should applied? The aim of this paper is to answer these questions among others. The authors assume that the readers of this paper come from varied backgrounds and experience. Some of you may not be totally familiar with these stability requirements whereas others may use them every day. It is hoped that this paper will be some enlightenment for the former and be an interesting review for the latter. In this paper the philosophy of sailing yacht stability will be presented. It will be also examined the criteria in force in countries such as Spain, United Kingdom, United States and The Netherlands among others and the assumptions upon which they are based will be highlighted. In order to clarify ideas two reference sailing yacht will be subjected to different criteria and compared their severity

Computational study of sail performance of a racing yacht

Es importante entender las caracteristicas del flujo y el comportamiento de las velas tanto para los navegantes como para los disenadores que quieren tener un empuje eficiente de la embarcacion. En este trabajo, se presenta la simulacion del flujo de aire alrededor de las velas, con una geometria final impuesta, y con un codigo CFD reproduciendo las medidas a escala real. El codigo numerico utilizado es un CFD viscoso basado en las ecuaciones RANS. Se han considerado tres combinaciones de velas: dos mayores y una mayor mas genova y los parametros estudiados principalmente son la sustentacion, resistencia, centro velico y el coeficiente de presion sobre las velas. Se han comparado los resultados obtenidos con datos experimentales y otros datos numericos procedentes de otros estudios. El estudio concluye que hay una buena concordancia entre los calculos numericos y los datos a escala real, mostrando la importancia de la utilizacion de estas herramientas numericas. It is important to understand flow characteristics and performance of sails for both sailors and designers who want to have an efficient thrust of yacht. In this article, the airflow around yacht sails with imposed final geometry is simulated using a CFD (Computational Fluid Dynamics) code reproducing full scale measurements. The code is a commercial viscous CFD based on Reynolds-averaged Navier-Stokes (RANS) equations. Three sets of sails are considered: two mainsails alone and one set of mainsail with jib and the parameters in study are mainly the lift, drag, center of effort and pressure coefficient over the sails. The results are compared with both experimental data and numerical computations obtained from other studies. It is concluded that there is good agreement between numerical calculations and full scale data, showing the importance of the use of numerical tools

Viability study of sailing propulsion combined with a conventional system

For many years now, sails have been used as a propulsion system. At present, they are restricted to recreational/sport crafts since the appearance of the first steam vessels in the beginning of the 19 th century. But in the last years, due to the increase of fuel price and the pollution of the environment, it is being studied the possibility to introduce again the sail as a propulsive method combined with other conventional systems. In this paper, it is studied the viability of using a sail as a propellant with other conventional systems of propulsion. After considering the concept of apparent wind, the range of use of this complementary propulsion is presented. The calculation methodology, the numerical simulations and the wind inputs from a specific route are also included

The effect of the Mast on Sail Performance

In this study, the airflow around a yacht sail with imposed final geometry is simulated using a CFD (Computational Fluid Dynamics) code reproducing full scale measurements. The code is a commercial viscous CFD based on Reynolds-Averaged Navier-Stokes (RANS) equations. The purpose of this article is to consider the effect of the mast on the performance of a sail. This research is related to a previously and published investigation written by the first author. That research was based on the aerodynamics of sails alone due to the lack of knowledge in regards to the geometry of the mast. The contribution of this new research is the calculation of how the mast affects sail performance using a recently acquired software. Furthermore, a methodology for the study of sails has been developed using this last software. The pressure coefficient on the sail, driving and side forces are computed among other variables.. The results are compared with both reference data obtained by full scale measurements. It is concluded that there is good agreement between the current results and the reference data

Drag Reduction trough Special paints Coated on the hull

The economic recession, the environmental impact as well as the continuous fossil fuel consumption encourage actions that focus on saving energy. In the vessels sector, one of the main objectives has always been to reach a hydro-dynamically optimum hull which gave the desired speed with minimum power. Hydrodynamic drag is basically divided into two parts: a) the friction between the water and the hull, and b) the wave generation due to the free-surface air-water. Presented in this paper, is the research which evaluates the possibility of friction-drag reduction by means of the coat of special paints on the hull. The study has been applied to a fishing cooperation vessel on which hydrodynamic aspects had already been analyzed by the ETSI Navales Model Basin. Two plates with different paints have been tested with a wet surface equivalent to the model used in the previous hydrodynamic test. Numerical simulations with a viscous code, which includes a roughness module, have also been carried out. The complete three dimensional system, including the free surface effect, has been considered. With these simulations it is expected to validate the roughness module of the commercial cod

Theoretical Analysis of SPH in Simulating Free-surface Viscous flows

A theoretical analysis on the performance, close to a free surface, of the most used SPH formulations for Newtonian viscous terms is carried out in this paper. After an introduction of the SPH formalism, the SPH expressions for the viscous term in the momentum equation are analyzed in their continuous form. Using a Taylor expansion, a reformulation of those expressions is undertaken which allows to characterize the behavior of the viscous term close to the free surface. Under specific flow conditions, we show that the viscous term close to the free surface is singular when the spatial resolution is increased. This problem is in essence related to the incompleteness of the kernel function close to the free surface and appears for all the formulations considered. In order to assess the impact of such singular behavior, an analysis of the global energy dissipation is carried out, which shows that such a free-surface singularity vanishes when the integral quantities are considered. Not with standing that, not all the SPH viscous formulas allow the correct evaluation of the energy dissipation rate and, consequently, they may lead to an inaccurate modelling of viscous free-surface flows

EU-CargoXpress: wind propulsion concept

The EU-CargoXpress project suggests the usage of sustainable energies to reduce the fuel consumption. The updated concept consists of hoisting the superstructure and using it as a sail together with the conventional propulsion. This paper presents the study of the sail performance by means of a computational analysis and wind tunnel tests. Moreover, a research of the energy saving in different operational areas has been conducted. It is concluded that there is a significant energy saving by using the superstructure as a sail which leads to a reduction of fossil fuel consumption and consequently, a reduction of greenhouse gas emissions

Reducción de la resistencia al avance de un buque mediante la aplicación de pinturas especiales al casco

La crisis económica, el impacto medioambiental y el consumo continuado de los combustibles fósiles propician cualquier iniciativa que conlleve un ahorro de energía. En el mundo de los buques, uno de los objetivos ha sido siempre el alcanzar un casco hidrodinámicamente óptimo que con un mínimo de potencia proporcione la velocidad deseada. Esta resistencia al avance se debe esencialmente a dos razones: a la fricción entre el agua y el casco del buque y a la generación de olas debido a la presencia de la interfase aireagua. El presente trabajo recoge las labores llevadas a cabo para evaluar la posibilidad de minimizar la resistencia debida a la fricción mediante la aplicación de pinturas especiales al casco del buque. El análisis se ha aplicado a un buque de cooperación en materia de pesca que ha sido estudiado hidrodinámicamente en el Canal de Ensayos Hidrodinámicos de la E.T.S.I. Navales. Para el estudio de la reducción de la resistencia de fricción se han ensayado dos planchas con una superficie mojada equivalente al modelo utilizado en los ensayos hidrodinámicos con dos tipos diferentes de pintura. También se han llevado a cabo cálculos numéricos con un código comercial de tipo viscoso con la posibilidad de evaluar la rugosidad. Se pretende también con ello proceder a la validación de dicho código para la consideración de la rugosidad

Numerical and Experimental Studies of Sail Aerodynamics

The purpose of this investigation was the determination of the aerodynamic performance of sails and gain knowledge of the phenomena involved in order to improve the aerody¬namic characteristics. In this research, the airflow around different sails in four scenarios was studied. The method to analyze these scenarios was the combination of numerical simulations and experimental tests by taking advantage of the best of each tool. Two different Com¬putational Fluid Dynamic codes were utilized: the ANSYS-CFX and the CD-Adapco’s STAR-CCM+. The experimental tests were conducted in the Atmospheric Boundary Layer Wind Tunnel at the Universidad de Granada (Spain), the Twisted Flow Wind Tunnel at the University of Auckland (New Zealand) and the A9 Wind Tunnel at the Universidad Polit´ecnica de Madrid (Spain). Through this research, it was found the three-dimensional effect of the mast on the aerodynamic performance of an IMS Class boat. The pressure distribution on a Transpac 52 Class mainsail was also determined. Moreover, the aerodynamic perfor¬mance of the 43ft and 60ft Dhow Classes was obtained. Finally, a feasibility study was conducted to use a structural wing in combination with conventional propulsions systems. The main conclusion was that this research clarified gaps on the knowledge of the aerodynamic performance of sails. Moreover, since commercial codes were not specifically designed to study sails, a procedure was developed. On the other hand, innovative experimental techniques were used and applied to model-scale sails. The achievements of this thesis are promising and some of the results are already in use by the industry on a daily basis. El propósito de este estudio era determinar el comportamiento aerodinámico de unas velas y mejorar el conocimiento de los fenómenos que suceden para optimizar las características aerodinámicas de dichas velas. En esta investigación se estudió el flujo de aire alrededor de diferentes velas en cuatro escenarios. El método para analizar estos escenarios fue la combinación de simulaciones numéricas y ensayos experimentales mediante el aprovechamiento de las ventajas de cada herramienta. Se utilizaron dos códigos de dinámica de fluidos computacional: el ANSYS-CFX y el STAR-CCM+ de la empresa CD-Adapco. Los ensayos experimentales se desarrollaron en el túnel de viento de capa límite de la Universidad de Granada (España), el túnel de viento de la Universidad de Auckland (Nueva Zelanda) y en el túnel A9 de la Universidad Politécnica de Madrid (España). Mediante esta investigación, se determinó el efecto tridimensional del mástil en un velero de la clase IMS. También se describió la distribución de presiones sobre una mayor de un Transpac 52. Además, se obtuvo el comportamiento aerodinámico de las clases 43ft y 60ft de los veleros Dhows. Finalmente, se llevó a cabo un estudio de viabilidad de la utilización de un ala estructural en combinación con sistemas de propulsión convencionales. La conclusión principal de esta investigación fue la capacidad de explicar ciertas lagunas en el conocimiento del comportamiento aerodinámico de las velas en diferentes escenarios. Además, dado que los códigos comerciales no están específicamente diseñados para el estudio de velas, se desarrolló un procedimiento a tal efecto. Por otro lado, se han utilizado innovadoras técnicas experimentales y se han aplicado a modelos de velas a escala. Los logros de esta investigación son prometedores y algunos de los resultados obtenidos ya están siendo utilizados por la industria en su día a día

A Wind Tunnel Investigation of the Aerodynamics of Sailing Dhows

This paper presents the results of experimental tests conducted to study the aerodynamic performance of sailing dhows. The investigation emerged from the interest shown by designers and sail-makers to understand how these sails perform, since they have never been studied before. The 43ft (13.1m) and 60ft (18.m) classes have been tested in a wind tunnel where the effects of varying several parameters were investigated. These parameters were: heel angle, apparent wind angle, bending and stiffness of the yard, optimization of the trimming and the influence of the mizzen on the mainsail. This is the first investigation where the aerodynamic performance of the lateen sails on sailing dhows has been investigated in a wind tunnel study