Sailing Principles - How Sails Work

• Sail Trimming
  You need to adjust the Sails regularly to ensure that the boat is getting the right driving power. This process is called Sail Trimming. There can be three scenarios - a Sail with the correct trim will lead to a maximum drive. If it is pulled in too much, it will result to less force. On the other hand, there will be no forward force if the Sail is let out too far. Let the Sail out and when it begins to flap like a flag, start pulling it in until it stops shaking.



• Reefing
  Another thing to know in order to understand how Sails work is the importance of Reefing, or the process of reducing the amount of Sail/s to suit the Wind condition. Reefing the Mainsail not only reduces the Sail area but also keeps the boat upright.
  
  Slab reefing is the most commonly used method of Reefing. In this process, the Sail is lowered by about one-third of the length of the Luff. A pre-loaded reef line is used to tighten the lower portion of the Sail through a cringle at the clew, and then hook through a cringle at the new tack.



• Wind coming from the side
  It is easy to understand how Sails work when the Wind is coming from the back. When the Sails are let out, the Wind pushes them, driving the boat forward. If this is the case, then the Sailboat will move sideways if the Wind is coming from the side. But this can be avoided and the boat can move forward through the use of the Centerboard or Keel. It resists the sideways force, therefore preventing the Sailboat from moving sideways. Keep in mind that the Keel should be well-shaped to resist the sideways force.



• How to deal with Leeway
  A well-shaped Keel will make the Sailboat move forward while moving slightly away from the direction where the Wind is blowing. This sideways drift caused by the wind is called Leeway. This increases when the Sailboat is steered further to windward. To lessen Leeway, especially when Close-Hauled, set the Centerboard fully down.



• Heeling
  This is a condition where the boat leans to one side due to Wind pressure. The boat can counteract this movement by a weighted Keel (in Keelboats) which provides extra force to resist the Heeling effect. The crew may also sit on the side deck, especially when Close-Hauled.