Mainsail trimming is not only a physically and mentally demanding role on a boat; it is one of the most crucial. You need a deep and subtle appreciation of sail shapes and the controls used to achieve them. Most significantly, the role requires an obsession with acquiring and maintaining speed. This book is here to help and it has been written in a groundbreaking way. Every effort has been made to simplify the subject and explain everything that you need to know without blinding you with science. Sailing terminology has been reined-in as much as possible and only information relating to mainsail trimming has been included. High quality photographs and illustrations are used throughout to simplify this complex subject. This is achieved by showing the sail shapes needed to make the boat go fast and stay under control. Only one sailing role is dealt with to further simplify the subject and make sailing more accessible to the newcomer. Table of Contents Foreword Creating lift & avoiding drag The mainsail & its controls The complete shapes How to sail fast upwind Offwind trim Hoisting, dropping & reefing Conclusion Glossary Index "Follow this clearly laid-out little book and you may well achieve that extra half-knot of boat speed." (Yachting Monthly) Uncover the secrets to sailing fast whilst remaining in control. Mainsail trimming is not only a physically and mentally demanding role on a boat; it is also one of the most crucial. You need a deep and subtle appreciation of sail shapes and the controls used to achieve them. Most significantly, the role requires an obsession with acquiring and retaining speed. This book is here to help and it has been written in a groundbreaking way. Every effort has been made to simplify the subject and explain everything that you need to know without blinding you with science. Sailing terminology has been reined-in as much as possible and only information relating to mainsail trimming has been included. High quality photographs and illustrations are used throughout to simplify this complex subject. This is achieved by showing the sail shapes needed to make the boat go fast and stay under control. Only one sailing role is dealt with to further simplify the subject and make sailing more accessible to the newcomer. Felix Marks is a successful racing and experienced cruising sailor in Australia and the UK. Also author of the popular sailing guide Jib Trimming. Mainsail Trimming An Illustrated Guide By Felix Marks John Wiley & Sons Copyright © 2007 Felix Marks All right reserved. ISBN: 978-0-470-51650-8 Chapter One Creating lift and avoiding drag Creating Lift with Airfoils Avoiding Drag with Airfoils Overall Mainsail Trimming: Goals and Means Sail Shape: Belly (Depth) Sail Shape: Leech (Twist) This section explains the basic principles of how sails work, including airfoils, lift and drag, sail depth and twist, and overall trimming goals. Creating Lift with Airfoils Before you start looking at sail shape, you must first understand a little of how sails work. When a boat is sailing, its sails are its engines. Sails use wind energy to create driving force. This force is harnessed to move a boat through (and sometimes over) the water. Sails can be used as airfoils or air dams. When the mainsail is used for upwind sailing it's used as an airfoil. Downwind sailing means the sail is used as an air dam. The crossover point is, approximately, when you're sailing on a broad reach (see Appendix C). Airfoils are special shapes that create lift and drag. Lift is the useful force that we use to make the boat go forward. Drag represents the forces that slow the boat down. Good sail trimming is about maximizing lift and minimizing drag. Having promised not to blind you with science, I will however, be giving you a little bit of theory you can't do without if you're going to understand lift and drag. It's pretty straightforward though! Higher pressure air tries to move towards lower pressure air. Anything between high and low pressure experiences a force towards the lower pressure too. For example, when you burst a balloon, the higher pressure air inside the balloon escapes. As it does so, the outside of the balloon is blown away - towards lower pressure air. The same principle applies to airfoils such as airplane wings or sails. Airfoils are used to create a pressure difference. This pressure difference generates lift. Lift is a force that we harness in sailing to make a boat move forwards. In aviation, this force is harnessed to elevate aircraft. Airfoil: Airplane Wing The engines on an airplane move the plane forward. This causes air to flow over the wings. There is a relative difference between the speeds at which the same amount of air travels over the wing compared to under. This is because the air traveling over the wing has further to travel. This relative difference in speed causes a pressure difference that lifts the win