iivanov191982 ® 25-Nov-2016 12:55

The Aero- and Hydromechanics of Keel Yachts


Year: 2015
Language: english
Author: J. W. Slooff
Genre: Technical book
Publisher: Springer International Publishing Switzerland, www.springer.com
ISBN: 978-3-319-13275-4
Format: PDF
Quality: eBook
Pages count: 645
Description: This book has come about as a follow-up on a course on the aero- and hydromechanics of sailing that was written by the author for the Heiner Sail Academy in the Netherlands in 2002/2003. The purpose of the course was to provide yachtsmen with (top-)amateur or (semi-) professional racing ambitions with a solid background of the aero- and hydromechanics of sailing. The ambition of the author was to do so in a manner that he could justify from his own background as a professional fluid dynamicist and a cruising yachtsman, while trying to keep the material accessible for attendees without profound academic schooling.
This, of course, is not the first book on the aero- and hydromechanics of sailing. A.C. Marchaj’s “Aero- hydrodynamics of sailing” (ISBN 0-7136-5073-7) is generally considered as ‘The Bible’ on the science and technology of sailing. And rightly so; it contains an incredibly broad and deep treatment of almost all aspects of sailing technology. Many readers, however, may find it difficult to find their way in Marchaj’s book, in particular if their objective is to find out in a relatively straightforward way about how and why sail boat performance depends on the configuration and trim of boat and sails.

Contents

1 Introduction.................................................................................................. 1
References...................................................................................................... 3
2 Sailing Yacht Geometry and Mass Properties........................................... 5
2.1 Introduction........................................................................................... 5
2.2 Hull Geometry....................................................................................... 5
2.3 Appendages ........................................................................................... 8
2.4 Rig and Sails ......................................................................................... 9
2.5 Mass Properties ................................................................................... 11
References.................................................................................................... 14
3 Forces, Moments and Motions.................................................................. 15
3.1 Notions and Definitions ...................................................................... 15
3.2 Forces Under Water............................................................................. 23
3.3 Wind Triangle...................................................................................... 28
3.4 Forces and Moments Above the Water Surface .................................. 31
3.5 Newton’s Law ..................................................................................... 37
Reference...................................................................................................... 39
4 Sailing: Basic Mechanics ........................................................................... 41
4.1 Equilibrium of Forces and Moments................................................... 41
4.2 ‘Geometry’ of the Mechanics of Sailing ............................................. 48
4.3 Driving Force, Side Force and the Efficiency
of Propulsion ....................................................................................... 52
4.4 The Role of the Sheeting Angle .......................................................... 64
4.5 Upwind Sailing.................................................................................... 68
4.6 Reaching, Running and Downwind Sailing........................................ 74
4.7 Speed Polar Diagram........................................................................... 79
References.................................................................................................... 81
5 Elements of Fluid Mechanics (Air and Water)........................................ 83
5.1 Introduction......................................................................................... 83
5.2 Pressure and Friction Forces ............................................................... 84
5.3 Static Forces........................................................................................ 87
5.4 The Conservation Laws of Fluid Motion ............................................ 88
5.5 A Consequence of Mass Conservation: The Venturi Effect ................ 90
5.6 A Consequence of Conservation of Energy: Bernoulli’s Equation ..... 92
5.7 Consequences of Conservation of Momentum: Scaling
Laws for Inertia Forces, Friction Forces and Pressure Forces............ 94
5.8 Physical Properties of Air and Water .................................................. 97
5.9 Sailing Yacht Reynolds Numbers...................................................... 100
5.10 High Reynolds Number Flows........................................................ 102
5.11 Boundary Layers, Wakes and Friction Drag ................................... 105
5.12 Boundary Layer Separation and Flow Detachment ........................ 112
5.13 Rotation, Circulation and Vortices .................................................. 115
5.14 Lifting Surfaces, Foil Section Characteristics................................. 121
5.15 Lifting Surfaces in Three Dimensions; Downwash and
Induced Drag................................................................................... 129
5.16 ‘Non-lifting’ Bodies ........................................................................ 148
5.17 Fluid Dynamic Interference Between Lifting Surfaces and
‘Non-lifting’ Bodies ........................................................................ 151
5.18 Unsteady, Periodic Flow Phenomena.............................................. 157
5.19 The Air-Water Interface, Surface Waves......................................... 171
References.................................................................................................. 181
6 Forces Under Water: Hydromechanics.................................................. 183
6.1 Functions of Hull and Appendages ................................................... 183
6.2 Righting Moments and (Static) Stability; Hydrostatics .................... 184
6.3 Hydrodynamic Side Force (Zero Heel)............................................. 191
6.4 Centre of Lateral Resistance, Hydrodynamic Moments,
Vertical Force .................................................................................... 207
6.5 Resistance.......................................................................................... 217
6.5.1 Decomposition of Drag......................................................... 217
6.5.2 Viscous Resistance ................................................................ 220
6.5.3 Induced Resistance................................................................ 231
6.5.4 Wave Making Resistance ...................................................... 237
6.5.5 Added Resistance in Waves................................................... 247
6.5.6 Propeller Resistance.............................................................. 268
6.6 Hydrodynamic Efficiency ................................................................. 269
6.7 Effects of Heel, Yaw Balance and Trim-In-Pitch.............................. 272
6.7.1 Angles in Different Coordinate Systems............................... 272
6.7.2 Effects of Heel on Vertical Force and Side Force ................. 273
6.7.3 Effects of Heel on Hydrodynamic Yawing Moment,
Static Directional Stability and Yaw Balance ....................... 280
6.7.4 Effects of Heel on Resistance ............................................... 285
6.7.5 Effects of Heel on Hydrodynamic Efficiency....................... 292
6.7.6 Effects of Trim-In-Pitch ........................................................ 294
6.8 Dynamic Stability and Sea-Keeping ................................................. 295
References.................................................................................................. 308
7 Forces Above the Water Surface: Aerodynamics.................................. 311
7.1 Functions of Hull, Rig and Sails ....................................................... 311
7.2 Wind and Wind Gradient................................................................... 313
7.3 Apparent Wind Angle, Angle of Attack and Sheeting Angle ............ 317
7.4 Single Sails........................................................................................ 319
7.4.1 Introduction........................................................................... 319
7.4.2 Flow and Force Characteristics of Sail Sections................... 320
7.4.3 Effects of a Mast or Head-Foil on Sail Section
Characteristics....................................................................... 332
7.4.4 ‘3D’ Effects: Effective Aspect Ratio..................................... 346
7.4.5 Factors Determining the Effective Aspect Ratio................... 356
7.5 Jib/Genoa Plus Mainsail.................................................................... 368
7.5.1 Interaction Mechanisms at Small Apparent Wind Angles..... 368
7.5.2 Lift and Drag......................................................................... 371
7.5.3 Effects of Gap, Overlap and Sheeting Angles....................... 374
7.5.4 ‘Optimal’ Camber.................................................................. 378
7.5.5 Large Apparent Wind Angles ................................................ 379
7.5.6 Additional Factors for Three-Dimensional Rigs:
Roach and Fractionality......................................................... 381
7.6 Aerodynamics of Other Yacht Components...................................... 385
7.6.1 ‘Windage’ and Parasite Drag................................................. 385
7.6.2 Interaction Mechanisms ........................................................ 387
7.6.3 The Flow About the Hull and Its Interaction with
the Sails ................................................................................. 390
7.7 Centre of Effort, Heeling, Pitching and Yawing Moments ............... 398
7.8 Foresails for Large Apparent Wind Angles: Spinnakers and
Gennakers.......................................................................................... 408
7.9 Effects of Heel and Trim-In-Pitch..................................................... 425
7.10 Unsteady Aerodynamic Effects....................................................... 438
7.11 Indicators: ‘tell tales’....................................................................... 449
7.12 Sail Trim: Adjusting Angle of Attack, Twist and Camber............... 454
7.13 Examples of Other Types of Rig..................................................... 461
References.................................................................................................. 468
8 Encore: Sailing; Aerodynamics Plus Hydromechanics ........................ 471
8.1 The Problem of Optimizing Boat Performance................................. 471
8.2 Upwind Performance, Dependence on Shapes of Hull and
Appendages....................................................................................... 480
8.3 Upwind Performance, Dependence on rig and Sails......................... 499
8.4 Directional Stability .......................................................................... 507
8.5 Dynamic Interactions ........................................................................ 517
8.6 Sailing in Waves................................................................................ 523
References.................................................................................................. 526
Retrospection.................................................................................................. 529
Appendices...................................................................................................... 531
Appendix A Some Basic Mathematical Notions .................................... 531
Appendix B Formulae for the Induced Angle of Attack
of a Lifting Surface ............................................................ 534
Appendix C Fluid Dynamic Forces on Lifting Surface
Configurations.................................................................... 535
Appendix D Approximate Formulae for the Position of the
Transverse Metacentre of the Hull of a Sailing Yacht........ 541
Appendix E Heuristic Model of the Effects of a Free Surface
on the Side Force and Induced Resistance of a
Surface Piercing Body........................................................ 543
Appendix F The Downwash (or Side Wash) Behind a Keel .................. 558
Appendix G Estimation of the Yawing Moment of a Sailing
Yacht Hull .......................................................................... 563
Appendix H Form Factors for the Viscous Resistance of
Sailing Yacht Components................................................. 566
Appendix I Kelvin Ship Waves ............................................................. 585
Appendix J Wave-Making Resistance ................................................... 587
Appendix K Natural Frequencies of Heaving, Pitching
and Rolling Motions .......................................................... 597
Appendix L Forces and Moments Due to Wave Encounter ................... 599
Appendix M A Model for the Effect of a Mast on the
Aerodynamics of a Thin Sail Section................................. 605
Appendix N Optimum Angle of Heel ..................................................... 613
Index................................................................................................................ 617
 
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