The Points of Sail describes a sailboat's course in relation to the wind direction.
A sailboat is either on port tack or starboard tack. If the wind is coming from anywhere on the port side, a sailboat is on port tack and if the wind is coming from the starboard side, then a sailboat is on starboard tack. For purposes of the IRPCS and the Racing Rules of Sailing, the wind is assumed to be coming from the side opposite that which the boom is carried.
Sailboats can't sail directly into the environmental wind or on a course that is too close to the direction from which the wind is blowing. The range which a sailboat can't sail is called the no-go zone. The no-go zone depends on the design of the sailboat, its rig, sails, on the strength of the wind and the sea state. Depending on the boat and the conditions.
When a sailboat attempts to sail into the no-go zone, the boat's sails don't produce enough lift to maintain forward momentum through the water. A sailboat in the no-go zone will eventually coast to a stop, with the rudder becoming less and less effective at steering.
A sailboat's ability to sail close to the wind is referred to as its "pointing" ability. A yacht designed primarily for racing can typically point within 30 or at worst 40 degrees from the wind direction, whereas one designed for cruising may only be able to point within 40 to 50 degrees of the wind direction. The size of the no-go zone varies, but all sailboats have one.
A sailboat's bow passes through the no-go zone as it tacks. When a sailboat is tacking through the no-go zone, it must maintain momentum to complete the tack. If a sailboat loses steerage before it exits the no-go zone, it is said to be "in irons," and may stop, return to the original tack, or begin to drift backwards.
If a sailboat attempts to tack at slow speed or loses forward momentum while heading into the wind, then the sailboat will come to a stop and the lack of flow over the rudder will cause the sailor to lose steering. When stuck head-to-wind, a sailboat is said to be "in irons". To get out of irons, one or more sails can be "backed" by sheeting or pushing them to windward. A sail that is backed to one side will push the bow to the other side, and the boat can then "pay off" in that direction. A sail that is backed further aft can make a boat begin to "sternboard" or sail backwards. When moving backwards it is possible to steer the boat out of the no-go zone using the rudder.
A sailboat is sailing close hauled (also beating to windward) when its sails are trimmed in tightly and it is sailing as close to the wind as it can without entering the no go zone. This point of sail lets the boat travel diagonally to the direction of the wind or "upwind". Sails act in the same way as wings; the flow of air over the outside of the curve creates lift that pulls the boat to leeward while the other forces such as the blades and crew weight help turn lift into forward motion. A sailboat is considered to be "pinching" or "feathering" if the helmsman sails above an efficient close-hauled course and the sails begin to luff slightly. This technique can be effective to maintain control of a sailboat on a windy day by "de-powering", or partially stalling the sail's lift. Pinching is otherwise inefficient.
When a sailboat is traveling almost perpendicular to the wind, this sailing direction is called reaching. A "close" reach is defined as somewhat toward the wind, and "broad" reach is defined as slightly away from the wind while a "beam" reach is defined as sailing with the wind precisely at a right angle to the sailboat. Reaching is the fastest way to travel for most modern sailboats.
This is an upwind angle between close hauled and a beam reach.
This is a course steered at right angles to the wind on either port or starboard tack. This is a precise point of sail, with sails put out at roughly 45 degrees.
The wind is coming from behind the boat at an angle. This represents a range of wind angles between beam reach and running downwind. The sails are eased out away from the boat, but not as much as on a run or dead run (downwind run).
Running or wing on wing (with two sails out on opposite sides like two wings)
On this point of sail the true wind is coming from directly behind the boat. Running can be dangerous point of sail because it is easy for an accidental jibe.
The mainsail is eased out 90 degrees to the boat or as far as it will go otherwise. When Running dead downwind the jib will collapse because the mainsail will block its wind. When a jib is gybed to windward for sailing wing on wing a whisker pole may be used to hold the sail out further catching more wind.
Steering is more difficult when sailing a running course because there is less pressure on the tiller and the boat is less stable, so boat can go off course easily. The tendency for a sailboat to turn off course when running can be dangerous in the event of an accidental jibe. Racing dinghies like the Laser, sail "by the lee" or with reverse windflow (from leech to luff)
When sailing on a dead downwind run it's easy to misjudge the real strength of the wind since the apparent wind is less (true wind minus boat speed).