| A sail can be likened to a wing in the way it | | | | we minimise the amount of sideways slippage, |
| works. When a wing moves forward, some air | | | | and maximise forward motion. |
| passes below the wing and some above. Due to a | | | | The more you pull the sail in, the smaller angle will |
| phenomenon known as the Coanda effect, air will | | | | become, which will result in a smaller force pushing |
| tend to follow an adjacent surface that curves | | | | you forwards. The smaller the forward force |
| away from the flow as long as the curvature of | | | | pushing the boat, the slower the boat goes. |
| the surface is not too great. When moving air | | | | Conversely, the more you let the sail out |
| changes direction, a force is generated. | | | | (basically up until the point before it starts to flap |
| A wing has a relatively flat bottom face, and a | | | | in the breeze), the greater the force forwards, |
| more rounded top surface. Since the wing has | | | | and the faster the boat can potentially go. |
| different shapes along its top and bottom faces, | | | | The fin acts in a similar fashion to the tyres on a |
| the air has to travel different distances, and thus | | | | car. They both minimise sideways movement and |
| at different speeds, across these faces. The | | | | allow easy forward movement. For example, if |
| faster moving air across the top face causes a | | | | you push a car on an angle, it will resist moving |
| region of low pressure, creating the lift that the | | | | diagonally, and instead will only move in a forward |
| wing needs. | | | | direction. |
| A sail works in a similar fashion. As wind enters | | | | For this reason the fin should be all the way down |
| the front of the sail, it is split, with some passing | | | | to minimise sideways slippage. |
| along the windward side of the sail, and some to | | | | Reaching Theory |
| the leeward side. The wind passing to the leeward | | | | Reaching is a comfortable and enjoyable angle of |
| side is forced to travel a longer distance, and | | | | sailing for many sailors. In the right conditions and |
| therefore has to travel faster, creating a low | | | | with a good setup you can get a dinghy up on |
| pressure region. | | | | the plane and moving across the water quickly. |
| Similarly to the lift created in a wing, the low | | | | Reaching is basically an extension of upwind sailing. |
| pressure created by changing the direction of the | | | | The wind is coming from roughly 90° to the |
| wind causes a force to be exerted on the sail. It | | | | boat, the sail is eased out to create a nice flow of |
| is this force which is used to move the boat. | | | | air over both sides of the sail, meaning that the |
| However, to utilise the force of the wind most | | | | forwards force is increased, and hence the boat |
| efficiently, the sail has to harness the wind's | | | | can potentially go faster. |
| power efficiently. And to accomplish this wind has | | | | Due to the fact that the sideways force is now |
| to deviate in direction over a sail's surface as | | | | smaller relative to the forwards force, sideways |
| smoothly as possible. To generate the lift | | | | slippage will be reduced. Some sailors opt to raise |
| required, wind passing over both sides of the sail | | | | the fin about 1/2 way to create less drag through |
| has to follow the curved profile of the sail surface. | | | | the water, and hence go faster. |
| This is achieved with the correct amount of curve | | | | Downwind Theory |
| in the sail, and having the correct angle of the sail | | | | Sailing downwind or running is basically when you |
| to the breeze. | | | | are sailing in the same direction as the wind is |
| To get the most amount of force moving the | | | | blowing. The wind is coming from behind the boat, |
| boat forwards, you need to deflect as much wind | | | | the sail is eased almost all the way out, meaning |
| as possible around the sail. | | | | that the forwards force is maximised. One |
| Upwind Theory | | | | problem with downwind sailing is that, since you |
| Upwind sailing can be a real challenge, and is an | | | | are travelling with the wind, the wind across the |
| aspect of sailing that takes a lot of practice and | | | | deck, and hence the wind that is being caught by |
| patience to develop. Some may initially find it a | | | | the sail, is less. Another issue is that since all the |
| little difficult to grasp the concept of upwind sailing, | | | | forces are (almost) in alignment, the boat can |
| but with the aid of vectors the process can be | | | | tend to become unbalanced, and it can roll over |
| explained a little easier. | | | | on top of you. |
| When wind enters the sail, it is forced to curve | | | | Due to the fact that the sideways force is now |
| around the belly of the sail. This curve in the sail | | | | minimal relative to the forwards force, sideways |
| can be represented by a force acting at 90° | | | | slippage will be reduced even more. Some sailors |
| to the sail. This force is made up of 2 | | | | raise the fin as high as possible without interfering |
| components - 1 acting sideways on the boat, and | | | | with the boom to create less drag through the |
| another pushing the boat forwards. By using a fin, | | | | water, and hence go faster. |