Apparent wind is the wind that's actually felt by anyone on a sailing boat. It's a combination of the true wind (which is the same as the sailing wind, another name for it) and the wind created by the motion of the boat (motion wind). These two winds are combined using vector addition - if you want to know about the maths. But you know exactly what the apparent wind is - you can feel it on your face when you're sailing!
Apparent wind sailing
Apparent wind sailing is a technique that was originally developed by the 18 Foot Skiffs in Australia, but is now commonly used by many high performance classes. It refers to the ability of a high performance boat to go downwind faster, by sailing two reaching legs rather than a single leg square to the wind. The boats go so much quicker on a reach than they do running, that the extra speed more than makes up for the extra distance sailed. When these boats are sailing the reaching legs, the apparent wind is much greater than when running - hence the name.
Asymmetric is a type of spinnaker. Instead of flying from an adjustable pole attached to the mast, it permanently attaches to a fixed central pole on the bow. It is sheeted from one corner, like a headsail, rather than swopping the sheet from one corner to another as on a conventional spinnaker.
Back refers to a change in the wind's direction. When the wind is described as backing, it is shifting to the left as you look into the wind. So if you are facing straight into a north-east wind (wind directions are always named by where they are blowing from) and it shifts to blow from the north, then the wind has backed.
Cavitation is the name a lot of sailors use for a hydrodynamic effect called Ventilation, which is when a vortex around a foil - usually the rudder - allows air from the surface to mix with the water around the foil and reduce its effectiveness. That gurgling noise coming from the rudder and indicating ventilation is usually followed by a distinct lack of turning on the part of the boat. The rudder stops working (also often described as stalling) and you hit whatever it was that you were trying to avoid.
Cunningham is a sail control, a system for applying tension straight down the luff of a sail, it's almost always seen on mainsails and often on headsails as well.
Current or tide wind
The current or tide wind is the wind created by the movement of water relative to the air. Imagine a perfectly still day on the land, with no wind at all. But you are standing beside a river that's flowing north at ten knots, and you can see wind ripples on the water. This is the current or tide wind - it blows at exactly the same strength as the tide or current is flowing. And it blows from the direction to which the tide or current is flowing. In this case, a current flowing north at ten knots will create a northerly current wind of ten knots.
Down-the-mine is sailing slang for what's also called a nose-dive - the bow of the boat buries itself underwater, usually by sailing fast into the back of a wave.
Fully-battened means a sail with sail battens that run the full width of the sail. The batten's tension is almost always adjustable to preset the curvature of the sail. Most often used in the mainsail but can be seen in some jibs as well.
Gnav is an upside down vang (hence the name, vang backwards...) - it pushes the boom down, from a point fixed on the mast above the gooseneck, rather than pulls the boom down from a fixed point below the gooseneck.
Head or sometimes header, refers to a change in the wind direction. If you are sailing upwind towards a fixed point like a buoy and the wind heads, then it has shifted to force you to sail further from the direct course to the buoy. An example; if you are sailing on starboard tack in a north-east wind, then if the wind shifts to the north it has headed.
Hiking means sitting in or on a boat, and leaning over the edge. Usually the crew put their feet under straps to hold themselves in place. If you want to win sailboat races, you have to be fit enough to hike hard.
Kite is popular sailing slang for any kind of spinnaker.
Layline refers to the final approach to a buoy or mark of the course when sailing upwind or downwind. If the final tack or gybe is made in exactly the right place, then the boat will sail to the mark at her optimum upwind or downwind angle - and she is on the layline. If a boat is not making the mark on that tack or gybe, she has not yet reached the layline. She will have to tack or gybe again before she can get to the mark (this is also called understanding).
Lee helm is an attribute of a sailing boat. When a boat has lee helm, it wants to turn away from the wind, and force will need to be applied to the rudder (so the rudder is at an angle to the boat's centre-line) to keep the boat sailing in a straight line.
Leeward is the side of the boat on which the wind is not blowing.
Lift refers to a change in the wind direction. If you are sailing upwind towards a fixed point like a buoy and the wind lifts, then it has shifted to allow you to sail closer to the direct course to the mark. An example; if you are sailing on starboard tack in a north-east wind, then if the wind shifts to the east it has lifted.
Line bias is the measure of which end of a start line is favoured by the wind. If the wind is blowing perpendicular to the line then neither end is favoured, but if it is blowing at an angle narrower than 90 degrees to one end, then that is the biased end of the line.
Motion wind is the wind you feel when you move. If the air is completely still, then when you walk, run, cycle - or sail - you will feel wind on your face. This wind is the wind created by your motion - and it's exactly equivalent in speed and exactly opposite in direction to the speed and direction at which you are moving. So if I run north at ten knots on a completely calm day, then I create a ten knot northerly motion wind (wind directions are always named by the direction they are blowing from).
OCS or short-hand for On the Course Side, refers to where a boat is when the starting signal goes. If you are OCS, you are on the wrong side of the line, and will be penalised for an early start - as long as the race committee see you.
Overstand refers to the final approach to a buoy or mark of the course when sailing upwind or downwind. If the final tack or gybe is made in exactly the right place, then the boat will sail to the mark at her optimum upwind or downwind angle. But if the final tack is made late, then the boat will be sailing to the mark at a wider angle than is the normal upwind angle. This is called overstanding. The boat has actually sailed past the right place to tack, and is reaching back towards the mark. Similarly, if the final gybe is made late on a run, then the boat will have to sail a narrower angle than she would normally sail to get to the mark. This is also called overstanding.
Pin is sailing slang for the end of the start line that is not marked by the principal committee boat. It is almost always the leeward end when you are on starboard tack.
Often used as slang for wind, 'more pressure' means more wind.
Recall is the name for a false start in sailing, when one or more boats are over the line early. There are two kinds of recall, an individual recall, when the number of boats over the line is small enough that they can all be clearly identified; and a general recall, when there are too many boats over the line to count, and the fleet has to be called back for a restart. An individual recall is usually indicated by flying International Code Flag 'X' and firing a gun. A general recall is indicated by flying the International Code Flag, 'First substitute', and firing two guns.
Righting moment is the amount of force available to keep the hull of a sailboat upright, when the wind is trying to push it over. Righting moment can come from the crew weight, as long as they are not sitting to leeward of the middle of the boat! And in keel boats it is also provided by the weight of the keel.
Rocking is what's called a kinetic technique, a body motion that promotes boat speed. In this case, specifically moving the crew weight across the boat to rock it from side to side, fanning wind into the sails. All kinetic techniques are limited to some extent by the sailing rules.
Sail battens are used to give additional support and shape to soft fabric sails. They are usually made from GRP and sit in pockets stitched onto the sail. Tension is usually applied by string or elastic. Almost all mainsails have battens, and some headsails.
Sailing wind is the wind that's created by the combination (by vector addition, if you're into the maths) of the land wind and the tide or current wind. If there is no land wind, but there is a five knot northerly tide wind, then the sailing wind will be a five knot northerly. If the land wind then increase to a five knot northerly as well, the sailing wind becomes a ten knot northerly.
Tack-line is the rope that holds the tack of an asymmetric spinnaker out to the end of the bowsprit or spinnaker pole.
Trapezes are wires attached high up on either side of the mast. The crew attach themselves - via a trapeze harness - to the wire and are supported while standing on the edge, outside the boat. This increases the righting moment available to keep the boat flat. It's also a lot less work and a lot more fun than hiking!
True wind is the wind that a boat is sailing in, and is the same thing as sailing wind. The true wind cannot be felt on a boat, but modern instrument systems can calculate it from measurements of the boat's heading, speed and apparent wind speed and direction.
Two lengths is a highly significant distance when it comes to rounding racing marks. Once boats have entered a circle drawn at a radius of two of their boat lengths from a mark or buoy, then the rules controlling their behaviour change. If you want to know how, read the rules!
Understand refers to the final approach to a buoy or mark of the course when sailing upwind or downwind. If the final tack or gybe is made in exactly the right place, then the boat will sail to the mark at her optimum upwind or downwind angle. But if the final tack or gybe is made too early, then the boat will have to tack or gybe again to reach the mark. This is called understanding.
Veer refers to a change in the wind's direction. When the wind is described as veering, it is shifting to the right as you look into the wind. So if you are facing straight into a north-east wind (wind directions are always named by where they are blowing from) and it shifts to blow from the east, then the wind has veered.
Weather helm is an attribute of a sailing boat. When a boat has weather helm, it wants to turn into the wind, and force will need to be applied to the rudder (so the rudder is at an angle to the boat's centre-line) to keep the boat sailing in a straight line.
Wild thing is a downwind technique in high performance catamarans. Using a combination of the skipper steering a slightly tighter course than normal and the crew sitting to leeward, the windward hull is popped out of the water. The reduction in resistance by sailing on a single hull makes the boat a lot faster and more than compensates for any extra distance sailed on the tighter downwind angle. The disadvantage is that in any breeze the crew sits in a firehose of spray unable to breathe, see or speak. They also require a good deal of confidence in the helmsman - but, hey, that's what crews are for.
Windward is the side of the boat onto which the wind is blowing.