How Do Sails Work? The Science Behind Sailing

We love getting students from all walks of life out on the water! We also love to teach the STEM principles behind our sailing and adventure sports! Have you ever wondered how a piece of canvas helps you sail? Read on to learn about the science behind sailing.

The Basics

The goal of sailing is to go with the wind in the right way to create enough velocity. In small sailboats there are usually two people per boat, the skipper and the crew. The skipper must control the main sail and steer. The crew is in charge of managing the smaller sail, the jib. The jib is a triangular sail fixed to the bow that improves the aerodynamics of the sails. The more sail area, the faster you will go.

For the sail to move with the wind, the sail must remain convex, so that the wind can continuously increase the pressure on the sail. While there are many ways to steer a sailboat, some are more effective than others. These positions are called points of sail. The points of sail are arranged like a clock, where the wind is blowing from 12 o’clock towards 6 o’clock and the way your boat is facing, is the hands. If the boat is facing directly into the wind, this point of sail is called “in irons”. You will not be able to sail, because the sail won’t be able to catch any wind. Some of the most efficient points of sail are those that allow sailors to position the sails so that they are close to the boat so that the wind can form a channel for the boat to pass through.

The Principles of Lift and Drag

The physical property of aerodynamic lift allows your boat to move forward even if the wind  is not directly behind the boat. Lift is the force that opposes the weight of an object and holds it up in the air. For example, imagine holding your arm out the window of a moving car. You can feel the force of the wind lifting your hand up and back. Similarly,  the wind blows against the sail from the side, this creates a force to the side and forward. The keel or centerboard, a heavy weighted part of the boat located at the bottom, helps keep the boat moving forward by providing a counter-force.

The opposite of lift is drag. Drag causes friction on the sail, hull, and centerboard/keel. So what can you do to reduce drag? Keep the mainsail trimmed! This will help develop as much power as possible and help the skipper to steer in the right direction. You can trim the sail by remembering those points of sail and using the sail to create lift. Keeping the weight of sailors in the boat will also help keep the boat balanced and will reduce drag.

Upwind Sailing

Usually, sailors want to be pushed by the wind. This is called downwind sailing. But what if you want to travel in the same direction that the wind is coming from? Unfortunately, a boat can’t sail directly into the wind, but it can sail in any direction that is greater than 45 degrees to the wind. If you have the patience to zig zag your way upwind, you can sail any direction you want! You can accomplish this by tacking. Tacking is a sailing maneuver that allows a boat to sail its bow towards the wind. This makes the wind blow on the other side of the sail so that you can make a turn and continue sailing upwind. By continuously tacking to either side of where the wind is blowing from, you will be able to reach your destination!

Interested in getting out on the water to try out these maneuvers yourself? Learn more about our adult and child sailing programs!