LEARNING OUTCOMES

This unit supplies students with the basic fundamentals of the sail aerodynamics and interaction with the hull, as well as technological and application concepts concerning the design methods and materials

AIMS AND LEARNING OUTCOMES

The units aims to provide the students with the basic principles of the aerodynamic - hydrodynamic related to the behaviour of sails and hulls. Lift and drag generation are deeply analysed and applied in the sailing boat environment, thus allowing the analysis of the sailing boat balance and performances. Sails (topology and shapes) are then studied in order to characterize their aerodynamic behaviour, highlighting the differences and the common aspects with the 3D airfoils. Keels and rudders are introduced and their effectiveness is analysed as a function of their basic geometrical parameters. Finally, the wave resistance is introduced and consequently the hull shape performances are studied and schemes of velocity prediction program are evaluated.

At the end of course the student shall be able to:

• Explain the basic concepts of lift and drag generations
• explain the fundamental concept of sailing
• explain and use the equations of equilibrium of a sailboat
• evaluate the various sources of drag and their effects on the boat performances
• explain the behavior of lifting surfaces in fluid mechanics
• implement and develop a velocity prediction program (VPP)
• analyze and judge the performance of a sailboat

TEACHING METHODS

The educational activities are organized into 52 hours of theoretical classes. Practical training activities concerning CFD simulations for sails and hulls and VPP programming may be performed.

SYLLABUS/CONTENT

• General Definitions.
• Sail typology as a function of the sailed course and of the wind intensity.
• Apparent wind: definition, analytical expressions and effects of the earth boundary layer, “Twist” effect in the apparent wind.
• Drag: the different resistance generation mechanisms, profile drag: skin friction drag, normal pressure drag. Definition of the involved physical parameters and of the methods to reduce the overall resistance. Basic aspects about the boundary layer and the boundary layer separation.
• Lift: lift generation mechanism, similarities and differences with respect to the flow around an airfoil. Circulation, Kutta-Joukowski law and expressions for the lift coefficient.
• Potential flow: usefulness and limit to the application.
• Thin airfoil theory.
• Two dimensional profiles: aerodynamic load distribution as a function of curvature and thickness, effects of the incidence angle variation.
• Induced Resistance: origin of the induced resistance. Effects of the aerodynamic loading distribution variations on the generated lift and resistance. Prandtl’s Lifting Line Theory.
• Sail twist and its effects in terms of lift and resistance.
• Phenomena of mutual interactions between different sails: typical issue the mainsail – jib case.
• Sailing boat equilibrium: forces and moments acting on a sailing yacht.
• Definition of a VPP (velocity prediction program) algorithm: required equations, iteration process, polar diagram of the boat performances, applications. VMG definition, examples for upwind and downwind course.
• Some considerations about hulls resistance and some systematic series. Effects of heeling: heel resistance. Added resistance in waves.
• Keel and rudder design: definition of the keel planform, practical conclusion regarding profile selection. Statistics of keels and rudders area.
• Examples of a whole design process.

RECOMMENDED READING/BIBLIOGRAPHY

• The Aero and Hydromechanics of Keel Yachts ” J.W. Slooff
• “The Symmetry of Sailing” Ross Garrett
•  “Aero-Hydrodynamics of a Sailing Yacht”  C. A. Marchaj
• “Aero-hydrodynamics and the performance of sailing yachts ” F. Fossati
• “Principles of Yacht Design” Lars Larsson
•  “Sail Performance”    C. A. Marchaj
•   “Sailing Yacht Design Theory”  Claughton – Wellicome – Shenoi
•  “Sailing Yacht Design Practice”  Claughton – Wellicome – Shenoi
•  “Maximum Sail Power” Brian Hancock
• “ High performance sailing ” F. Bethwaite
• “Aero-Hydrodynamics and the Performance of Sailing Yachts” Fossati, F..