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Nautical Terms Relating to
Sails, Rigs and Sailing.

Nautical terminology is confusing for not-so-salty boatbuilders and sailors. Here is the result of my research on sail terminology

If you plan to do any reading on sails and sailing you will need to know these sail terms or at least where to find the meanings. HERE!

If you want me to add another word, just send me an email and I'll add it. I'm hoping here to include the most important terms used to describe sails and sailing and to make it easier for folks who are trying to read and are getting bogged down with the terminology.

The drawings are mine, I'm not a terrific illustrator. Add a new word.

Many beginning boat builders and not so novice find sail terminology confusing, you are not alone.

Test your knowledge with my Sail Quiz

sail terminology and definitions

Sail Words Defined

Or more accurately just FOIL The shape of a Sail or daggerboard or wing or blade (of a propeller, rotor or turbine) or as seen in cross-section. An airfoil-shaped body moved through a fluid such as water and produces a force. The component of this force perpendicular to the direction of motion is called lift. This is what moves a sail boat.
Aspect Ratio
The ratio of the height against the width. If a sail is 14 feet high and 7 feet wide it has an aspect ratio of 2:1 expressed as "two to one". High narrow sails will have a higher first number while short wide sails such as sprit or lugs will have smaller first number. 1:1 is an almost square sail.
Chafing gear usually placed on a spar or rigging to protect sails from damage from rubbing against them.
Flexible stiffening used to help maintain the shape of a sail. They are almost always used if the Leech of the sail has a pronounced Roach. The Battens are usually placed in batten pockets, but sometimes are attached directly onto the sail such as in Junk Sails.
Some battens span the whole width of the sail while others are only a fraction of the width. Some battens are quite strong and have significant structural functions, this is particularly true in sails such as batwings, and Junk sails.
Bernouilli Principle
for an inviscid (not thick) flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Bernoulli's principle can be used to explain the lift force on an airfoil. For example, if the air flowing past the forward surface of a boat sail is moving faster than the air flowing past the rear facing surface, then Bernoulli's principle implies that the pressure on the surfaces of the wing will be lower forward than rear. The forces will then suck the boat forward.
The nautical term for a pulley. A block either changes the direction of a line, such as pulling down on a halyard to bring a sail UP, or if many blocks are used together increase the mechanical advantage.
Bolt Rope
A rope sewn or attached on the edge of the sail to help reinforce it. When raising a sail the boltrope along the Luff is often slid in the mast groove then raised. The sail may also be attached to the boom by sliding the foot bolt rope through the groove in the boom. A line from the Clew attaches to the Outhaul to tighten the foot of the sail.
The spar at the foot of the sail that keeps the sail stretched out at the bottom. A sail may be laced to the boom or be loosed footed and only tied at the ends or may have a groove and bolt rope.
A spar that extends from the bow of a boat to extend the reach of a headsail.
Boom Vang
Sometimes called Kicking Strap, is a line or block and tackle system used to pull the boom down in order to control the shape of the mainsail. It can be used to control sail twist. In some boats a solid rod is used to PUSH the boom down since this is the reverse of a VANG it is called a GNAV!!
Used to describe the curve in a sail when under power. The idea camber changes as conditions change and are subject to much debate as to the ideal shape. Draft
Centre of Effort
The point on the sail where the force of the wind appears to act. The Center of Effort is the point against which the Centre of Lateral Resistance (provided by the keel and hull plus rudder) is balanced against. When a designer draws the sail plan he tries to balance the sail such that there is no strong force causing the boat to change course if the rudder is let go.
Because the balance of a rig depends also on the trim of the sails, load, angle of approach and angle of sails, it is not possible to have a perfect balance at all points of sail. When several sails are used, the combined centre of effort of the rig is used.
Sailors speak of Lee Helm and Weather Helm when speaking of the tendency of a boat to go away from the wind (downwind), and the tendency of a boat to round up into the wind. Lee helm is the least desirable balance.
When new boat builders come to choose and build a rig they need to consider the balance of the sail and hull.
Centre of Lateral Resistance
The point at which the forces generated by the hull and foils including the daggerboard, keel and rudder, appear to act. It is balanced by the Centre of Effort. The relationship and balance of the centre of effort and the centre of lateral resistance results in the balance of a rig. It can lead to Lee Helm, Weather Helm or Neutral Helm.
Damage to a sail cause by rubbing. Good sails are built with extra protection in areas which are prone to chafe. Chafing gear.
The lower or aft corner of a sail . The corner of the sail which is at the lower corner away from the mast. The outhaul often attaches to the Clew. The lower corner nearest to the mast is called the Tack, the corner at the top of the mast is the Head in a triangular bermudian sail and a Throat in a Spritsail. The top corner of a Sprit, lug or other 4 sided sail, is the Peak.
An eye through which to pass a Rope. On Sails cringles are often grommets at the 3 or 4 corners. (Strictly speaking a cringle is the hole itself but cringle usually also includes the reinforcing grommet) There are also cringles at the reefing points. Sailors might speak of the clew cringle, tack cringle, etc.
Also sometimes acting as a Downhaul, pulls the sail Luff down and adjusts the forward tension of the luff along the mast. It is not always present if the boat also has a boom-vang (Kicking strap), Casually referred to as "smart pig"
Sail grade polyester fabric designed to be used as sailcloth. It is available in many sizes and weight. Dacron has stabilizing coatings which resist stretching and improve the durability of the sail.
The degree of curvature of a sail in a horizontal cross section. The draught ( or belly) of a sail influences the shape of the airfoil. Modifying the draft of the sail modifies its lift characteristics. Different levels of draught are used depending on the angle of the boat to the wind. Camber
A line which tightens to luff to control the shape of the sail. The downhaul or Cunningham acts on the tack pulling the sail down. Downhauls are also used to pull a sail down. In a Junk rig there could be a downhaul on each batten.
In a Junk Rig, a piece of hardwood or plastic with a hole which are used in the sheets controlling the individual battens. Used instead or alongside blocks.
A device which helps lead a line clear of obstructions. A fairlead also helps line up a line into a cleat.
A general term for different types of sail set on the foremost mast, the foremast. A headsail.
The lower edge of a sail. It is bounded by the tack at the mast and the clew. The foot is parallel to the boom. A sail can be loose footed and only attach to the boom at the tack and clew, or it can be laced or attached all along the boom.
Loose footed sails can also be sails which do not have booms. In this case the Mainsheet is attached to the clew.
To roll up or fold and secure. In Junk Rigs the sail is furled by lowering it into its lazy jacks.
Mechanism to easily reduce the size of a sail. Often sailors mean the jib or genoa furler which rolls up the sail on the forestay. Various other forms of furlers have been designed such as a mainsail furler which rolled up the main onto the boom, with limited success!
It is more difficult to maintain an ideal shape with sails that are on a furler but the convenience and safety is appreciated by non racers.
One of several headsails which can be set on a Bermudian Rig. It is a large triangular sail which overlaps the mainsail. The name Genoa is used when the foot of the headsail is longer than the distance from the forestay to the mast. Otherwise the headsail is referred to as a jib. The number 130,140 etc is a percentage which refers to the relationship of the length of the foot of the genoa and the distance between the forestay to the mast. The larger the number the larger the sail.
A giant 4 sided sail that is set between 2 masts.This sail is often made of light fabric such as nylon and set between the fore and main masts. It has no spars and acts somewhat like a spinnaker. Unlike a spinnaker it is not primarily a downwind sail.
The top point of a triangular sail, There is usually a Head Board and a head cringle at the head of the sail. The main halyard attaches to the head of the sail. In square sails such as sprit and lugs the top side of the sail is the Head and the corner nearest to the mast is the Throat. The corner further from the mast is the Peak.
Head Board
A reinforcement often made of aluminium or strong composite or plastic, which reinforces and stiffens the head of a sail. The main halyard attaches to the headboard.
A line which raises and lowers a sail. Halliard. (Haul-Yard)
The front sail. In modern rigs it is often a jib or genoa. If the boat has a furler then the headsail is unrolled and set at the desired size, otherwise the sail is hanked on by clips to the forestay and hoisted and lowered each time. Foresail
To lift, such as to hoist a sail. To hoist heavy loads a block and tacle is often used. The hoist of a sail is its height on the mast.
1. A secure line to which a safely harness line is clipped so the wearer can move about with the safety line moving along the line.
2. A line which is passed inside the snap hooks of a jib and helps to douse the sail. Once the halyard is loosed the sailor or his kids, pull on the jackline to lower the sail. It can be routed to the cockpit to avoid having to go on deck.
Triangular sail which is flown along the mainstay. One of the important functions of the jib is to funnel the airflow along the front of the main to improve airflow and lift. Jibs come in several sizes. The smallest jib is a storm jib and is often made of bright material strongly reinforced. The heavy weather jib is also quite a small headsail. The working jib is the most commonly used jib on that boat. A jib foot is technically no longer than the distance between the mast and the forestay. If it is longer it is then a Genoa.
If the boat is equipped with a furler then the size of the jib-genoa can be adjusted as the wind changes and only one sail is necessary.
When going downwind if the wind crosses the back of the boat the sail also goes to the other side. This can be quite violent and dangerous if unexpected. If going into the wind one speaks of tacking, if going downwind one jibes. The sail has to be carefully controlled while jibing. Many a head has been bonked by an unexpected jibe. Some rigs such as lugsails and Junk sails have less dramatic jibes because part of the sail is forward of the mast. This reduces the force with which the sail goes over.
Jib Headed
Pointed triangular sail
Junk Sail
A form of balanced lug sail developed in China and other Asian countries. It is characterized by a series of panels with full battens each controlled by individual lines. This control the set and twist of sail. Junk Rigs are well liked because they are docile and easy to control, can easily be reefed simply by lowering the sail. The bottom of the sail folds down into a lazy jack which keeps the bottom of the sail tidy and out of the way. Junk sails distribute strain over large surface and for that reason relatively weak materials can be used for the sailcloth. It was not unusual to see quite flimsy materials used in the past. The down side of the junk sail is the weight of the battens and the complexity of having many blocks and lines running from the end of the battens. My page on the advantages and disadvantages of the junk rig
Kicking Strap
Another term for a Boom-vang. It attaches about a third of the way out on the boom and to the mast and helps shape the sail. It also helps prevents the boom from lifting in a gust.
Lazy Jacks
Lines running from the top of the mast to the boom and used to control a sail as it is lowered or reduced. The lazy jacks are placed on both sides of the sail and form a sort of basket to receive the sail.
The offset between the Center of Lateral Resistance CLR of the keel, hull and rudder AND the the Center of Effort CE of the sails. This determines the balance of the rig.
Lee Helm
The tendency of a boat and rig to point away from the wind. A boat with lee helm is difficult to control. Weather helm is the opposite where the boat tends to point into the wind. Lee and weather helm are the result of imbalances between the sailing rig Center of effort and the hull/foils centre of lateral resistance.
The side of a sail that runs between the end of the boom and the top of the mast in a triangular sail, and parallel to the mast between the end of the boom (clew) and the peak of a 4 sided lug or sprit. The Leech is the most rear part of the mainsail. IF it has a bulge in the edge then there will be battens to keep the leech stiff. The Roach is the name of the bulge in the Leech.
A force generated when a fluid passes over a foil. Sails are foils that create an area of lower pressure on the downwind side of the sail and this creates a force that pulls the boat forward. Keels and rudders are also foils that also create lift. Lift in this case does not mean up and down motion but rather forward motion. A foil in an airplane wing is oriented sideways such that lift is actually up and down. The principles are the same.
The edge of the sail which is against the mast. It is either laced on or attached to hoops, or else the sail rope fits in a slot in the mast. Sometimes plastic slugs are attached to the sail and these slide into the mast slot.
The top corner of the luff is the head on the triangular sail and a Throat in a sprit or lug sail. The bottom corner is the Tack. The shape of the Luff is controlled by a Downhaul or Kicking strap.
The principal sail of a rig, sets on the main mast. In some rigs it is not necessarily the largest sail. Sometimes a Genoa or a Spinnaker is larger in area than the mainsail.
The line which controls the angle of the mainsail. The mainsheet is usually attached to boom and to the floor of a boat, or to a traveler. The mainsheet can be a single line but more often consists of one or more blocks. If there is no mast the mainsheet attaches to the clew.
Mast Track
A groove or track on the back of the mast. It is used to attach the sail to the mast either with little slugs which slide in the track or with a Bolt Rope sewn in the sail.
A small sail often carried at the stern of a boat. It is very useful in balancing a sail plan which otherwise would have Lee Helm. In old ships the mizzen mast and sails were aft of the mainmast.
A line running from the clew at the end of the boom to the end of the boom. Used to tighten the foot of the mainsail and control the shape of the sail.
A line used to secure usually a spar which moves against another. There might be a parrel holding the jaws of a boom or gaff against the mast. The parrel keeps the spar in place but allows it to move. There are often small beads called parrel beads strung on the line to improve movement.
Parrel Beads
Wooden or other material beads which help a spar roll along a mast. They are threaded onto a parrel and act as a roller bearing.
The corner of a 4 sided sail which is opposite the mast along the top. The Throat is near the mast, the head is the side which runs between the throat and the peak. In a Sprit sail, the sprit attaches to and lifts out the peak. On a lug sail, the gaff attaches to the peak and the throat.
Peak Halyard
The line used to raise the end of a gaff. It is attached to the Peak from the mast.
Rake, the angle of the mast forward or back.
To sail with the wind on the side of the boat "abeam". A reach is a point of sail.
Reefing Points
Points at which a sail can be reduced (reefed). Usually there are grommets to reinforce these points.
Reduce sail by lowering or tying up the sail, to reduce the force of the sail, usually when the wind picks up.
Reefing Lines
Lines which run from the sail reefing points, to the boom and then often to the base of the mast or to the cockpit. Tightening the Reefing lines while releasing the main halyard allows the sail to drop some and be reduced.
Sometimes the small lines used to tie the sail after it has been reefed are called reefing lines. A reef knot is sometimes used on these small ropes.
Re Enforcing patches
Sails are reinforced along the corners and along the reefing points by sewing in reinforcing patches. This helps support the sail and limit stretching, in areas of high stress.
The bulge in a sail's Leech when the cut is rounded to increase sail area. The Roach is supported and shaped by battens.
A piece of yarn or line used to fasten a sail to a spar.
Ropes are sometimes sewn inside or along the edge of sails to improve strength, control the stretch, or help raise the sail.
To sail with the wind coming from behind.
Running Rigging
Lines in a boat that move such as halyards or sheets. Standing rigging does not move, stays are standing rigging.
A last ditch effort to quickly reduce sail in a sprit rig. By detaching the snotter, the sprit spar is released and the sail is immediately halved. The peak of the sail can then be fastened to the mast resulting in a triangular sail (with very poor shape.) In my rig the sprit is usually found to go into the water pushed by the tension of the peak. If the snotter accidentally comes undone an accidental scandalizing can occur :)
The line which is often kept in hand and used to adjust the angle of the sail. The mainsheet usually runs from the boom to either a traveller or a block in the cockpit and often has several blocks to add mechanical advantage.
A sailing move used by double ended proas (and sailing canoes) instead of tacking or jibing. The boat changes direction and the previous bow becomes the stern in the new tack. Usually the mast is slid to a new position or its rake is reversed. It has the advantage of always presenting the same side to the wind taking full advantage of the ama or side hull of an outrigger.
A line which is attached to the lower end of the sprit and which is used to lift the sprit and tighten the peak of a sail.
A large billowing headsail used in downwind sailing. The jib is brought down and the spinnaker raised. The only spar is a spinnaker pole which extends the clew of the spinnaker out. Spinnakers can be symmetrical or asymmetrical. They can be quite huge. Spinnakers are often made of colourful nylon. In gusty changing winds spinnakers can be challenging sails to fly and can wrap around anything they can reach. The advantage is tremendous downwind sail area. They are casually referred to as a Kite or a Chute.
Is a spar which is used in spritsails to support the peak and keep it high. It is tightened by a snotter. The sprit attaches to the peak to lift it high.
A leg of mutton sprit is a triangular sail with a sprit at right angle to the mast which is used to extend the sail.
Four sided sailing rig of great antiquity. Typically it uses a sprit spar to support the peak. It may or may not have a boom. It has the advantage of being very simple and allowing a great deal of sail on a very short mast.
Recent test have claimed that the sprit sail is the most efficient sail rig in common use. My spritsail page link. Although it is not a high pointing rig, it is highly efficient and fast on other points of sail. Sprit sails with no booms were made famous by the Thames barge which used spritsails as their main sail. It has the advantage of folding up to get out of the way or get through narrow spots. A disadvantage of this rig is the difficulty in reefing. Sailors release the snotter thus immediately unpowering half of the sail. This is called scandalizing the sail! no kidding!
Standing Rigging
Lines in a boat that don't move such as stays. Running rigging moves often through blocks.
Stay Sail
a fore-and-aft rigged sail whose luff can be affixed to a stay running forward (and most often but not always downwards) from a mast to the deck, the bowsprit, or to another mast.
The corner of the sail nearest the bottom and next to the mast. The downhaul often attaches to the tack. The reefing tack is a higher position along the mast where the sail can be reefed. A Reefing Clew is located a corresponding distance up fro the boom along the leech.
Tell Tails
Light pieces of tape or yarn that flutter in the wind. They are attached to the sails in various spots and help show how the wind is flowing around the sails as they are trimmed.
Topping Lift
A line which runs from the top of the mast to the end of the boom and is used to support the boom when the sail is lowered. It sometimes attaches to the back stay. A topping lift is sometimes used to support a spinnaker pole.
A moving attachment for the main sheet. The traveller runs on a track that stretches from starboard and port. It allows the mainsheet attachment to move and improve the set and shape of sail. The mainsheet block is attached to a "car", which slides along it in either direction improving the trim of the mainsail. The advantage of using a traveller is that it maintains a desired sail shape and sheet tension, while allowing the sail angle to be adjusted.
Weather Helm
When the Center of Effort of the Sail and The Centre of Lateral Resistance of the hull and foils is not in balance, the boat can either try to head into the wind and have Weather Helm, or try to turn downwind and have Lee Helm. When the rig is perfectly balanced with the boat it has Neutral Helm. Most sailors prefer a slight Weather Helm. It is safer since the boats heads into the wind and stalls if the tiller is let go. This could happen when someone falls overboard. Lee helm makes a boat more difficult to handle and reduces its pointing ability.
A spar on a mast from which sails are set. In a lug sail the top boom is called a yard. The halyard or halliard pulls on the yard and raises the sail

I try to be accurate and check my information, but mistakes happen. I don't pretend to be complete either.

email me if you find mistakes, I'll fix them and we'll all benefit: Christine