Abstract
This chapter revisits the combined effects of the aero- and hydromechanic forces and there mutual interaction in some further detail, with particular attention for the performance aspects. The first section addresses the problem of optimizing boat performance and the role therein of so-called Velocity Prediction Programs (VPP). Next, the dependence of (upwind) boat performance on the shapes of hull, sails and appendages is illustrated through applications of a VPP developed by the author. The chapter (and the book) is concluded with discussions on directional stability, dynamic interactions in rolling and yawing motions and sailing in waves.
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Notes
- 1.
For multiple sails there will, in general, be a sheeting angle δ and angle of attack α for each individual sail.
- 2.
Additional variables are involved for yachts with a trim tab, water ballast or a canting keel.
- 3.
If the incidence of the keel would be set such so as to reduce the angle of leeway of the centre plane of the hull, the resistance of the hull would be marginally smaller. There will also be an effect on the yawing (“Munk”) moment of the hull and an associated change in the induced resistance of the rudder due to the different balance in yaw.
- 4.
For q = 279, the expression for the heel forcing factor Kφ becomes equal to the so-called Dellenbaugh angle, a rough measure of the stiffness of a yacht (Larsson and Eliasson 1996).
- 5.
Note that this behaviour was already anticipated in Sect. 7.4.
- 6.
Made dimensionless by hydrodynamic quatities (made dimensionless by hydrodynamic quatities (ρH, V b, Sk, LWL)).
- 7.
Recall at this point that a larger value of xk implies an increased ‘lead’ (distance) between the centre of effort (CE) of the sails and the centre of lateral resistance (CLR) of the underwater body.
- 8.
Note that the apparent wind angle β is 35° rather than the 30° in the preceding figures.
- 9.
Partly also because the effect of the rudder on the hydrodynamic damping was not taken into account. It is estimated that, with rudder, the hydrodynamic damping would increase by ≅ 25 %.
References
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Slooff, J. (2015). Encore: Sailing; Aerodynamics Plus Hydromechanics. In: The Aero- and Hydromechanics of Keel Yachts. Springer, Cham. https://doi.org/10.1007/978-3-319-13275-4_8
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