The RC Racing Yacht Explained


How to use this book.

Many readers may think that section 2 is more than is required to understand a yacht. However reference is made in section 3 to the many aspects of “theory” which are essential in order to follow the text. It is really best to browse section 2 before tackling section 3 and then go back to look at section 2 carefully as the need arises.


This book can be downloaded using a modern printer to appear like the original on A4 paper. The aberrations in the presentation of the text on the screen are the result of the change to html that has to be made to upload to the web.


Click on any chapter to open it.


                                         Table of Contents


Section 1

            Chapter 1      Introduction                                                                                     1


Chapter 2      The monohull racing yacht.                                                           3


Section 2

Chapter 3     The “theory” needed to understand model yachts.                       6


Mathematical equations and units.  The triangle of forces.  Relative motion.  Framed structures. Centre of gravity.  Centre of volume.  Centre of area.  Second moment of area.  The concept of pressure.  Flotation.  Stability of floating vessels.  Metacentre and metacentric height.  Potential energy and kinetic energy.  Pressure energy.


            Chapter 4     Air and water as they act on a yacht.                                              17



The structure of water when it is at rest.  The motion of water near to the surface resulting from wind blowing over it.  Pressure variation in water at rest.


Air as a gas.  The structure of a gas.  The action of wind on a lake.


            Chapter 5     The resistance to the motion of a surface vessel.                          21


Introduction.  Forms of motion of surface vessels. Skin drag.  Resistance to motion resulting from wave making.  The idea of a critical speed.




            Chapter 6     The aerofoil                                                                                       26


Flow patterns and aerodynamic lift.  The effect of an aerofoil on the upstream flow.  Pressure distribution round an aerofoil.  Separation.  Lift and drag.  Aerofoil data.  The effect of aspect ratio.  Aerofoils at high angles of attack.


Section 3

            Chapter 7     Leeway and the thrust versus speed graph for a model yacht      35


            Chapter 8     How a yacht beats to windward.                                                     37


Tacking.  Apparent wind.  Leeway.  Vector diagram for the beating yacht.  Angle of attack of the main sail.  Forces on sails


            Chapter 9     Flow visualisation for the beating yacht.                                        43


The Hele-Shaw equipment.  The shape of sails.  The single sail in the Hele-Shaw rig.  The Bermuda rig in the Hele-Shaw equipment.


            Chapter 10    The polar performance diagram explained using the swing

                                                rig version of the Bermuda rig.                                          50


 The polar performance diagram.  The swing rig.  Combined force on a swing rig. The sailing diagrams.  Implications of the polar diagram.


            Chapter 11     The real flow over a Bermuda rig                                                   56

 Vortices and breakaway.  Practical testing.  Photographs.


            Chapter 12     The geometry of the Bermuda rig as it is used in model

                                                 yachting                                                                              60


The sheeting mechanism. The winch.  The requirements of the rig.  Sheeting the fore sail.  Sheeting the main sail.  Sheeting the sails together.  Changing to smaller rigs.  Selecting a drum size.  Position of the sheeting eye on the fore deck.


            Chapter 13     Flow visualisation for the conventional Bermuda rig.                  64


            Chapter 14     The sailing diagrams for  a conventional Bermuda rig.               66


Sailing diagrams for boom angles from 0° to 90°. Sailing diagrams for reaching and running.


            Chapter 15     The mechanical arrangements of sailing rigs.                               70


The standing rigging used for the Bermuda rig.  The sail mountings.  The swing rig.


            Chapter 16     The sails.                                                                                           74


The design of sails for model yachts.  The sail plan.  The profiles.  The main sail.  The fore sail.


            Chapter 17     The fin.                                                                                              80


Introduction. The section of the fin.  Surface finish.  Choice of section area of fin.  Shape of fin.


            Chapter 18     The rudder.                                                                                       85


The directional control of a yacht.  The wing/stabiliser system.  The fin and rudder system.

Changing course.  Design of the rudder.


            Chapter 19     The bulb.                                                                                           93


Low drag profile for round bulbs.  Bulbs for yachts with draught restrictions.  Surface finish.


            Chapter 20     The hull of a racing yacht                                                                96


Strength.  Flotation.  Stability.  Leeway and turning.  The shape of the hull.


            Chapter 21     Conclusion                                                                                        104


The sailing rig.  The hull and the rig.  Sailing in light winds.  The model yacht as a whole.  Design guidelines for model yachts. Post script