After walking and riding, sailing is probably one of the oldest forms of transportation. Since ancient history, people have used the wind to propel their sea crafts. Goods were transported & traded, 'new' islands & continents were discovered, even wars were fought with the help of sailing boats / ships. Not all of them were big ships. From the Unangan with their Baidarkas in the north, to the Polynesian in the south, small crafts with sails were quite a common sight around the world. Materials and designs of these crafts have changed over the centuries, while the basic principle of sailing still remains the same, even in our modern times.
How does a sail work?:
With the wind from behind it is pretty obvious. The sail acts like a big parachute or kite which catches the wind, and propels the boat forward. While sailing in an angle into the wind ( beating ), the physics are much more complex and interesting.. When the wind fills the sail it creates the shape of a wing. When the air flows around the sail, it does so faster on one side than on the other. This creates a force, which pushes the sail, and with it the boat, forward and to the side. To sail straight ahead we need the help of either a daggerboard (mounts through the kayak) or a lee board (fixed on the side ). The daggerboard acts like an underwater wing which applies lateral resistance. When the sail pushes the boat forward and to the side, the water hits the daggerboard at a slight angle, and the wing principal ( the water flowing faster on one side than the other ) creates a second lateral force, but in the opposite direction to that of the sail. These two lateral forces equal each other out, and only the forward momentum is left. This description is quite simplified, but gives you a rough understanding of what is happening on and under your boat.
No sailing boat, regardless if it's a kayak or a 30' Cat, can sail directly into the wind. The Sail can't create power, instead it just flutters in the wind. The non-sailable zone is called the 'no sail zone', or 'dead zone'. It equals about 90° (depending on the boat ), 45° left and right of the wind direction. The sailable directions are divided into: close reach, beam reach, broad reach and running. To sail as high on the wind as possible is called 'close hauled'.
Beating or 'working': To reach an upwind destination, a technique called 'beating' or 'working' is used. By sailing close-hauled with the wind coming from one side, then tacking (turning the boat through the eye of the wind) and sailing with the wind coming from the other side, it is possible to reach any upwind destination.
Different sorts of sails:
On a kayak we can differentiate between two groups of sails: up-wind sails and down wind sails. Down wind sails are the simplest sort of sail, and probably the most common. They enable the kayak to run with the wind, some more advanced designs allow a broad reach or even a beam reach. There are a wide range of commercial downwind sails available, e.g. the Wind Paddle, or the Pacific Action Sail, just to name a few. Sometimes things we carry on the kayak can double as a down wind sail. It only takes a bit of creativity. An umbrella, an emergency blanket or a jacket on a paddle or a stick, a kite, even your back /body can function as a sail and provide downwind assistance.
Upwind sails allow the Kayak to sail into every sailable direction. They are more sophisticated and often (semi ) permanent systems with a proper mast and base, a dagger or leeboard, and they often have a bigger sailing area. Some sailing kayaks have furlable sails and are equipped with one or two outriggers to keep the kayak upright in higher wind speeds or even have a Jib ( a smaller sail in front of the main sail ). Good examples for upwind sail systems are the Hobie Island Kayak, Balogh Sail Designs, or the KayakSailor. A very good summary about different kayak sails and sailing systems for kayaks can be found here.
http:Most common design//www.sit-on-topkayaking.com/Articles/SurfSail/Sail.htm
Here some more sailing basics:
• The dagger board should be lowered when sailing "close to the wind", but can be raised or folded up on downwind courses to reduce drag. On a close haul the daggerboard should be fully down, and while running, over half way up, or folded backwards ( AI ).
• Trimming the sail is a topic which fills whole books. But as a general rule a sail should be pulled in until it fills with wind, but no further than the point where the front edge of the sail (the luff) is exactly in line with the wind. Let it out until it starts to flap along the front edge, and then pull it in until it stops. In general, the “closer to the wind” you sail the tighter you will have to sheet in your sails. This means that when you sail into the wind you will pull the sails in tighter than if you sail with the wind behind you.
• Trim is the weight distribution along the kayak. While packing the kayak the goal is to spread the weight evenly to achieve an 'even keel'. On an upwind course, more weight can normally be moved forward to reduce drag. When running, more weight is put to the rear of the kayak. How much depends on the kayak. An Adventure Island, for example, sails better with more weight on the back.
So give sailing a go, it is easy and lot's of fun!