The Molossian Naval Academy

BASIC SEAMANSHIP


CATEGORIES

TERMINOLOGY | SIGNAL FLAGS | NAVIGATION | WATCHSTANDING | ROPEWORK | SAILING | SAIL


Terminology

Sailors use many traditional nautical terms for the parts of or directions on a vessel; starboard (right), port (left), forward or fore (front), aft (rearward), bow (forward part of the hull), stern (aft part of the hull). Vertical spars are masts, horizontal spars are booms (if they can hit you), gaffs (if they're too high to reach) or poles (if they can't hit you).

Other terms

Walls are called 'bulkheads' or 'ceilings', while the surfaces referred to as 'ceilings' on land are called 'overheads'. Floors are called 'soles'. The toilet is traditionally called the 'head', the kitchen is the 'galley'. Sails in different sail plans have unchanging names, however.

Sailing terms have entered popular language in many ways. "Broken up" was the fate of a ship that hit a "rocky point." "Pooped" refers to the aftermost deck of a ship, taken from "puppis" the Latin word for "stern". "In the doldrums" referred to being becalmed, windless, especially in the narrow band of hot windless water "the doldrums", near the equator. "Adrift" meant literally that a ship's anchor had come loose, and the ship was out of control near land and therefore in serious danger. "Keel-hauled and hung out to dry." was the rather nasty process of attaching a sailor to a rope, and drawing him under the sailboat while underway, and then hanging him from a yard-arm (under his shoulders usually, not by his neck), where officers and crew could mock him. This was a particularly unpleasant punishment; apart from the risk of drowning, the sailor would be lacerated by the barnacles on the ship's hull.

International maritime signal flags

The system of international maritime signal flags is a way of representing individual letters of the alphabet on ships or in nautical situations.

The flags can also be used to signal other things than alphabetical messages. For example, divers will often raise the flag representing the letter A as a marker to other sea traffic in the area.

The flags are also used, with a different set of special meanings, in yacht racing and dinghy racing, where (for example) the P flag is used as the "preparatory" flag to indicate an imminent start, and the S flag means "shortened course".


Navigation

Modern methods

There are several different branches of navigation, including but not limited to:

celestial navigation - navigation by observation of the sun, moon and stars
pilotage - using visible natural and man made features such as sea marks and beacons
dead reckoning - using compass and log to monitor expected progress on a journey
waypoint navigation - using electronic equipment such as radio navigation and satellite navigation system to follow a course to a waypoint
position fixing - determining current position by visual and electronic means
collision avoidance using radar

Knowing the ship's current position is the main problem for all navigators. Early navigators used pilotage, relying on local knowledge of land marks and coastal features, forcing all ships to stay close to shore. The magnetic compass allowing a course to be maintained and estimates of the ship's location to be calculated. Nautical charts were developed to record new navigational and pilotage information for use by other navigators. The development of accurate systems for taking lines of position based on the measurement of stars and planets with the sextant allowed ships to navigate the open ocean without needing to see land marks.

Later developments included the placing of lighthouses and buoys close to shore to act a marine signposts identifying ambiguous features, highlighting hazards and pointing to safe channels for ships approaching some part of a coast after a long sea voyage. The invention of the radio lead to radio beacons and radio direction finders providing accurate land-based fixes even hundreds of miles from shore. These were made obsolete by satellite navigation systems.

Traditional maritime navigation with a compass uses multiple redundant sources of position information to locate the ship's position. A navigator uses the ship's last known position and dead reckoning, based on the ship's logged compass course and speed, to calculate the current position. If the set and drift, due to tide and wind, can be determined, an estimated position can also be calculated.

Periodically, the navigator needs confirm the accuracy of the dead reckoning or estimated position calculations using position fixing techniques. This is done by correctly identifying reference points and measuring their bearings from the ship. These lines of position can be plotted on a nautical chart, with the intersection being the ship's current location. Addition lines of position can be measured in order to validate the results taken against other reference points. This is known as a fix.

Celestial navigation systems are based on observation of the positions of the Sun, Moon and stars relative to the observer and a known location. Anciently the home port was used as the known location, currently the Greenwich Meridian or Prime Meridian is used as the known location for celestial charts.

Navigators could determine their latitude by measuring the angular altitude of Polaris any time that it was visible. Determining latitude by the sun was a little more difficult since the sun's altitude at noon during the year changes for a given location.

Calculating the anticipated altitude of the sun for a given day and known position is done easily using Calculus. But prior to its invention by Newton around 1700, tables of the sun's altitude during the year for a known port were used. The sun's angle over the horizon at noon was measured, and compared to the known angle at the same date as the known port. Local noon is easily determined by recording periodic readings of the altitude of the sun. Since periodic readings of the altitude will plot a sine wave, the maximum reading is the one used for local noon.

Longitude is calculated as a time difference between the same celestial event at different locations. Noon was an easy event to observe. Local noon is determined while shooting the azimuth as described above. The time of the maximum altitude is easily determined by interpolating between periodic readings. The time of noon at the known location is carried by the navigator on an accurate clock. Then the local time of local noon is observed by the navigator. The difference of longitude is determined knowing that the sun moves to the west at 15 degrees per hour.

The need for accurate navigation led to the development of progressively more accurate clocks. Once accurate clocks were available, detailed tables for celestial bodies were created so that navigational activities could take place anytime during the day or night, rather than at noon.

In modern celestial navigation, a nautical almanac and trigonometric sight-reduction tables permit navigators to measure the Sun, Moon, visible planets or any of 57 navigational stars at any time of day or night. From a single sight, a time within a second and an estimated position, a position can be determined within a third of a mile.

Conceptually, the angle to the celestial object establishes a ring of possible positions on the surface of the Earth. A second sighting on a different object establishes an intersecting ring. Usually the navigator knows his position well enough to pick which of the two intersections is the current position. The math required for sight reduction is simple addition and subtraction, if sight-reduction tables are available. The numerous celestial objects permit navigators to shoot through holes in clouds. Most navigation is performed with the sun and moon.

Accurately knowing the time of an observation is important. Time is measured with a chronometer, a quartz watch or a short wave radio broadcast from an atomic clock.

A quartz wristwatch normally keeps time within a half-second per day. If it is worn constantly, keeping it near body heat, its rate of drift can be measured with the radio, and by compensating for this drift, a navigator can keep time to better than a second per month.

Traditionally, three chronometers are kept in gimbals in a dry room near the center of the ship, and used to set a watch for the actual sight, so that no chronometers are ever risked to the elements. Winding the chronometers was a crucial duty of the navigator.

The angle is measured with a special optical instrument called a "sextant." Sextants use two mirrors to cancel the relative motion of the sextant. During a sight, the user's view of the star and horizon remains steady as the boat rocks. An arm moves a split image of the star relative to the split image of the horizon. When the image of the star touches the horizon, the angle can be read from the sextant's scale. Some sextants create an artificial horizon by reflecting a bubble. Inexpensive plastic sextants are available, though they have less accuracy than the more expensive metal models.

The LORAN system is based on measuring the phase shift of radio waves sent simultaneously from a master and slave station. Signals from these two point establish a hyperbolic curve for possible positions. A third source along with dead-reckoning will generally resolve to a single position.

GPS uses 3D trilateration based on measuring the time-of-flight of radio waves using the well-known speed of light to measure distance from at least three satelites. This can be accomplished using low cost quarts clocks because the satellites send time correction signals to the GPS receivers.

History

In the West, navigation was at first performed exclusively by dead-reckoning, the process of estimating one's present position based on the navigators' experience with wind, tide and currents.

Most sailors have always been able find absolute north from the stars, which currently rotate around Polaris, or by using a dual sundial called a diptych.

When combined with a plumb bob, some diptychs could also determine latitude. Basically, when the diptych's two sundials indicated the same time, the diptych was aligned to the current latitude and true north.

Another early invention was the compass rose, a cross or painted panel of wood oriented with the pole star or diptych. This was placed in front of the helmsman.

Latitude was determined with a "cross staff" an instrument vaguely similar to a carpenter's angle with graduated marks on it. Most sailors could use this instrument to take sun sights, but master navigators knew that sightings of Polaris were far more accurate, because they were not subject to time-keeping errors involved in finding noon.

Time-keeping was by precision hourglasses, filled and tested to 1/4 of an hour, turned by the helmsman, or a young boy brought for that purpose.

The most important instrument was a navigators' diary, later called a rutter. These were often crucial trade secrets, because they enabled travel to lucrative ports.

The above instruments were a powerful technology, and appear to have been the technique used by ancient Cretan bronze-age trading empire. Using these techniques, masters successfully sailed from the eastern Mediterranean to the south coast of the British Isles.

Some time later, around 300, the magnetic compass was invented in China. This let masters continue sailing a course when the weather limited visibility of the sky.

Around 400, metallurgy allowed construction of astrolabes graduated in degrees, which replaced the wooden latitude instruments for night use. Diptychs remained in use during the day, until shadowing astrolabes were constructed.

After Isaac Newton published the Principia, navigation was transformed. Starting in 1670, the entire world was measured using essentially modern latitude instruments and the best available clocks.

In 1730 the sextant was invented and navigators rapidly replaced their astrolabes. A sextant uses mirrors to measure the altitude of celestial objects with regard to the horizon. Thus, its "pointer" is as long as the horizon is far away. This eliminates the "cosine" error of an astrolabe's short pointer. Modern sextants measure to 0.2 minutes of arc, an error that translates to a distance of about 0.2 nautical miles.

At first, the best available "clocks" were the moons of Jupiter, and the calculated transits of selected stars by the moon. These methods were too complex to be used by any but skilled astronomers, but they sufficed to map most of the world. A number of scientific journals during this period were started especially to chronicle geography.

Later, mechanical chronometers enabled navigation at sea and in the air using relatively unskilled procedures.

In the late 19th century Nikola Tesla invented radio and direction-finding was quickly adapted to navigation. Up until 1960 it was commonplace for ships and aircraft to use radio direction-finding on commercial stations in order to locate islands and cities within the last several miles of error.

Around 1960, LORAN was developed. This used time-of-flight of radio waves from antennas at known locations. It revolutionized navigation by permitting semiautomated equipment to locate geographic positions to less than a half mile. An analogous system for aircraft, VOR and DME, was developed around the same time.

At about the same, TRANSIT, the first satellite-based navigation system was developed. It was the first electronic navigation system to provide global coverage.

Watchstanding

Watchstanding, or watchkeeping, in nautical terms concerns the division of qualified personnel to operate a ship continuously around the clock. On a typical sea going vessel, be it naval or merchant, personnel keep watch on the bridge and over the running machinery. The generic bridge watchstanders are a lookout and an officer or mate who is responsible for the safe navigation of the ship. Safe navigation means keeping the vessel on track and away from dangers as well as collision avoidance from other shipping. An engineering specialist ensures that running machinery continues to operate within tolerances and depending on the vessel, this can also be accomplished from the bridge. A secondary function of watchkeeping is the ability to respond to emergencies, be it on own ship or involving other ocean users.

Duration

Watch durations will vary between vessels due to a number of reasons and restrictions. The traditional three-watch system from the days of sail where the ships company was divided into three and the day divided into six watches of four-hours duration, such that an individual would keep two four-hour watches each day separated by an eight-hour time for sleep or recreation. Examples of other systems include 4 by 6-hour and 7's and 5's when a warship has half its ships company on watch at a time.

Ropework

Ropework is commonly defined as the set of processes of making and repairing ropes; some, however, also include any other work that can be done with ropes, such as tying knots and splicing.

Actually, only a few of the "ropes" on a boat are called ropes, most are called lines.

Ropes or wires that hold up masts are collectively known as standing rigging and are called shrouds or stays (the stay connecting the top of the mast to the bow is called the forestay or headstay).

Ropes or wires that control the sails are known collectively as running rigging or lines. Those that raise sails are called halyards while those that strike them are called downhauls. Ropes that adjust (trim) the sails are called sheets. These are often referred to using the name of the sail they control (eg. "main sheet", or "jib sheet").

Ropes used to tie the boat up when alongside are called docklines.

Some knots: 1. Splice 2. Manrope knot 3. Granny knot 4. Rosebud stopper knot 5. Matthew Walker knot 6. Shroud knot 7. Turks head knot 8. Overhand knot, Figure-of-eight knot 9. Reef knot or Square knot 10. Two half hitches

There are some ropes: A few examples, the bell rope (to ring the bell), a bolt rope (attached to the edge of a sail for extra strength), a foot rope (on old square riggers for the sailors to stand on while reefing or furling the sails), and a tiller rope (to temporarily hold the tiller and keep the boat on course). A rode is what keeps an anchor attached to the boat when the anchor is in use.

Making a rope

To make a rope, take a long length of twine or yarn and tie it to a rod of strong material. Loop it around a second rod, held at a distance. Take it back to the first rod, loop it around, and then once more back to the second, to which it is then tied. There should be three lengths of twine running between the two rods. Each person holding a rod then moves backward until the lengths are taut and then begins turning his rod counterclockwise. This continues until the twine has been tightly twisted; at this point, the securing knots are untied. The twine is then secured to the rods again (as if the piece of three twisted lengths is one) and run between them as before was, with three lengths between the rods. The holders again pull the material taut and begin turning, this time in the opposite direction. When the rope is tightly twisted, each end is whipped (see below) and then cut between the whipping and the rod.

Whipping frayed ropes

A whipping knot is a type of knot used to hold the frayed end of a rope together. The simplest sort, the common whipping, is done by taking a two-foot-or-greater length of strong string, forming a loop with it, three or four diameters of the rope in length, and lying it on the rope near the frayed end. The rest of the length is then tightly wrapped without overlapping around the rope, moving up the loop. When the end of the loop is nearly covered, pull the remaining free length of the string through the loop and then pull on both ends, which will pull the end of the loop under the whipping. Cut off the end of the rope close to the edge of the whipping and then cut off the two free lengths of string.

A somewhat simpler method is merely to cut off the fraying and wrap a few layers of tape, usually electrical tape, around the cut end.

Fusing frayed ropes

Fusion is a method of repairing a frayed end of a nylon or plastic rope through use of heat. Cut off the fraying at the end, light a candle or cigarette lighter, and hold the cut end a few inches above the flame until the fibers have melted and fused together. Allow the end to cool before touching it or setting it down.

Another method of fusing, somewhat weaker, is simply to cut the end, dip it in paint, and allow it to dry.

Sailing

Sailing is motion across a body of water in a sailing ship, or smaller boat, powered by wind.

How sailing works

The force of the wind is used to create motion by using one or more sails. The movement of air over the sails acts in the same way as air moving over an aircraft's wing. Just like on an airplane, air flowing over the sail is deflected and accelerated. This generates lift, which acts to pull the sail, and thus the boat ahead, but also slightly downwind. The downwind component is offset by an underwater hydrofoil (centerboard or keel), whose shape resists lateral movement while offering little resistance to forward motion. Without a keel or centerboard, sailing upwind or across the wind would be virtually impossible. (Other sailing hydrofoils include daggerboards and leeboards).

The lifting force of the sails also acts to lean the boat over to one side, which is called heeling. This is counteracted by ballast, either in the form of dense material located in the keel (usually lead or iron) or in the form of human or water ballast located near the windward rail.

Today, for most people, sailing is a hobby. Pleasure sailing can be further divided into two areas: Racing and Cruising.

In ancient times (see Odysseus), ships used following or rear-quarter winds. Therefore, they had to wait in port or at sea for the right wind directions.

Basic sailing techniques

Turning a sailing boat

There are four basic maneuvers a sailing boat can perform while underway. They are:

Tacking is turning the boat so that the bow passes through the eye of the wind (or "no go zone").
Gybing (or wearing) is turning the boat so that the stern of the boat turns through the wind. Gybing causes the boom to swing from one side to the other, sometimes rapidly, as the wind catches the leach of the mainsail on its new upwind side.
Heading up is turning the boat to sail closer to the direction the wind is coming from.
Bearing away (or falling off) is turning away from the direction the wind is coming from.

Trim
An important aspect of sailing is keeping the boat in "trim". And remembering to let go of the rope. To achieve this a useful mnemonic (memory aid) is the phrase:

Can This Boat Sail Correctly?

This helps the crew to remember these essential points;

Course to Steer - Turn the boat using the wheel or tiller to the desired course to steer. See points of sail. This may be a definite bearing (e.g steer 270 degrees), or towards a landmark, or at a desired angle to the apparent wind direction.
Trim - This is the fore and aft balance of the boat. The aim is to adjust the moveable ballast (the crew!) forwards or backwards to achieve an 'even keel'. On an upwind course in a small boat, the crew typically sit forward, when 'running' it is more efficient for the crew to sit to the rear of the boat. The position of the crew matters less as the size (and weight)of the boat increases.
Balance - This is the port and starboard balance. The aim, once again is to adjust weight 'inboard' or 'outboard' to prevent excessive heeling.
Sail - Trimming sails is a large topic. However simply put, 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.
Centreboard - If a moveable centreboard is fitted, then it should be lowered when sailing "close to the wind" but can be raised up on downwind courses to reduce drag. The centreboard prevents lateral motion and allows the boat to sail upwind, and also provides stability to keep the boat from rolling over. A boat with no centreboard will instead have a heavy permanent keel built into the bottom of the hull, which serves the same purposes.

Running Downwind

Sailing the boat within 30 degrees of straight downwind is called a run. This is the easiest point of sail, but it can also be the most dangerous. Sailing upwind gives you the everpresent possibility of stopping the boat easily by steering into the wind. Running gives a sailor no such easy out. Be careful and either use your boom vang or adjust the mainsheet to prevent an accidental gybe.

Beating an upwind course

A basic rule of sailing is that it is not possible to sail directly into the direction the wind is coming from. Generally a cruising boat can sail 45 degrees off the wind, a racing boat may aproach 35 degrees. However since it is often necessary to move towards the wind direction, it is necessary to 'beat' upwind.

Beating is simply a series of 'tacks' where the boat sails as close to the wind on each tack as possible, and then switches sides and repeats the process. By this method, it is possible to travel directly into the wind. The heavier the wind the harder the beat, and since you are sailing into oncoming waves at an angle, boat movement can be heavy. This movement can feel like the boat is beating its hull into the waves, hence the name. Since the boat is sailing over oncoming waves, a beat will feel faster than its actually moving.

During a beat, it is important to watch your heading, since the wind will tend to push an unbalanced boat into or away from the wind, depending on the balance problem. If you find yourself having to overcorrect at the helm for sail pressure into the wind, then you are in a condition called weatherhelm, and you are actually slowing the boat with your rudder. To correct this, reduce sail.


Reducing sail

An important safety aspect of sailing is to adjust the amount of sail to suit the wind conditions. As the wind speed increases the crew should progressively reduce the amount of sail. On a small boat with only jib and mainsail this is done by furling the jib and by partially lowering the mainsail, a process called 'reefing the main'.

Reefing basically means reducing the size of a sail without changing them. Ideally reefing does not only result in a reduced sail area but also in a lower center of effort from the sails, keeping the boat more upright.

There are three core methods of reefing the mainsail: - Slab reefing, which involves lowering the sail by about one-quarter to one-third of its luff length and tightening the lower part of the sail using an outhaul through a cringle at the new clew, and hook through a cringle at the new tack. - In-mast (or on-mast) roller-reefing. This method rolls the sail up around a vertical foil either inside a slot in the mast, or affixed to the outside of the mast. It requires a mainsail with either no battens, or newly-developed vertical battens. - In-boom roller-reefing, with a horizontal foil inside the boom. This method allows for standard- or full-length horizontal battens.

Mainsail furling systems have become increasingly popular on cruising yachts as they can be operated shorthanded and from the cockpit in most cases, however, the sail can become jammed in the mast or boom slot if not operated correctly. Mainsail furling is almost never used while racing because it results in a less efficient sail profile. The classical slab-reefing method is the most widely used. Mainsail furling has an additional disadvantage in that its complicated gear may somewhat increase weight aloft. However, as the size of the boat increases, the benefits of mainsail roller furling increase dramatically.

Sail trimming

As noted above, sail trimming is a large subject. Basic control of the mainsail consists of setting the sail so that it is at an optimum angle to the wind,(i.e. no flapping at the front, and tell tales flowing evenly off the rear of the sail).

Two or more sails are frequently combined to maximise the smooth flow of air. The sails are adjusted to create a smooth laminar flow over the sail surfaces. This is called the "slot effect". The combined sails fit into an imaginary aerofoil outline, so that the most forward sails are more in line with the wind, whereas the more aft sails are more in line with the course followed. The combined efficiency of this sail plan is greater than the sum of each sail used in isolation.

More detailed aspects include specific control of the sail's shape, e.g.:

reefing, or reducing the sail area in stronger wind
altering sail shape to make it flatter in high winds
raking the mast when going upwind (to tilt the sail towards the rear, this being more stable)
providing sail twist to cope with gusty conditions

Heeling

When a boat rolls over to one side under wind pressure, it's called 'heeling'. As a sailing boat heels over beyond a certain angle, it begins to sail increasingly inefficiently. Several forces can counteract this movement.

The buoyancy of that part of the hull which is being submerged tends to bring the boat upright.
Pressure on the centreboard or keel moving at a slight 'leeway' angle through the water tends to balance the rolling force.
Raising the centreboard can paradoxically increase leeway, and therefore reduce heeling.
A weighted keel provides additional force to right the boat.
The crew may move onto the high (upwind) side of the boat, called hiking, changing the centre of gravity significantly in a small boat.
They can trapeze where the boat is designed for this. The underwater shape of the hull relative to the sails can be designed to make the boat tend to turn upwind when it heels excessively: this reduces the force on the sails, and allows the boat to right itself.
The boat can be turned upwind to produce the same effect.
Wind can be spilled from the sails by 'sheeting out', i.e. loosening the sail.
Lastly, as the boat rolls farther over, wind spills from the top of the sail.
Most of the above effects can be used to right a heeling boat and to keep the boat sailing efficiently: if however the boat heels beyond a certain point of stability, it can capsize.

Sailing close to the wind
How close a boat can sail to the wind depends on the wind speed, since what the boat "sees" is the apparent wind, i.e., the vector sum of the actual wind and the boat's own velocity. The apparent wind is what the windex on top of the mast shows. Because of this, people often talk about how close a boat can sail to the apparent wind. A good, modern sloop can sail within 25 degrees of the apparent wind. An America's Cup racing sloop can sail within 16 degrees, under the right conditions. Those figures might translate into 45 degrees and 36 degrees relative to the actual wind. The angles at which the wind meets the boat are described by the points of sail.

Sailing safety

First and foremost:

Learn to swim!
Wear a life vest!
Sailing is intrinsically dangerous, since water is not our natural element. All sailors therefore should take precautions, and when engaged in publicly organised activities they must take certain precautions, as detailed by the authority which regulates the training or racing.

Safety measures include:

Provision of a safety boat for rescue purposes
Appropriate first aid and firefighting equipment
Carrying of a knife suitable for cutting rigging or netting which may entrap a sailor underwater
Wearing of buoyancy aids
Understanding and practice of man overboard procedures such as the Anderson turn, the Williamson turn, and the Scharnow turn.

Also, know the 'rules of the road':

Port tack gives way to Starboard tack (when the paths of two boats on opposite tacks cross, the boat with its port side to windward must give way)
Windward gives way to the leeward, or downwind boat (if on the same tack)
Overtaking boat gives way if above do not apply
Non-Commercial Powerboats usually give way to sailboats (but be careful in shipping lanes, and use common sense)
It is everybody's responsibility to avoid a collision, and avoiding action must be taken if these rules are ignored.

Sailing hulls and hull shapes

Sailing boats can have one, two, or three hulls. Boats with one hull are known as monohulls, while those with two or more are known as multihulls. Multihulls can be further subdivided into catamarans (two hulls), and trimarans (three hulls). A sailing boat is turned by a rudder which itself is controlled by a tiller or a wheel. Smaller sailing boats often have a stabilising, raisable, underwater fin called a centreboard (or daggerboard); larger sailing boats have a fixed (or sometimes canting) keel. As a general rule, the former are called dinghies, the latter yachts.

Multihulls use flotation and/or weight positioned away from the centre line of the sailboat to counter the force of the wind. This is in contrast to heavy ballast that can make up to 1/3 of the weight of a monohulled sailboat. In the case of a standard catamaran there are two similarly sized and shaped narrow hulls connected by a deck superstructure. Another catamaran variation is the proa. In the case of trimarans, which have an unballasted centre hull similar to a monohull, two relatively smaller amas are situated parallel to the centre hull to resist the sideways force of the wind. The advantage of multihulled sailboats is that they do not suffer the performance penalty of having to carry heavy ballast, and their relatively smaller hulls reduce the amount of drag caused by friction and inertia when moving through the water.

Types of Sails and layouts

On a modern yacht, the mainsail or main is usually the primary driving sail, triangular in shape, and fixed to the largest (or often the only) mast. A headsail, either a jib or genoa, is set in front of the mainsail, attached in such a way that the trailing edge extends back alongside the main. This is also known as an overlapping headsail (pronounced hedsal). Two or more headsails can be used. In addition, some sailboats, ketches and yawls, have another smaller mast called the mizzen mast, on which is set a smaller sail similar to the mainsail and called the mizzen sail.

A spinnaker is a large, full sail that is only used when sailing off wind either reaching or downwind, to catch the maximum amount of wind.

Sailing regulations

There are two very basic rules for avoiding a collision at sea: 1) Power gives way to sail 2) Port gives way to starboard. This second point means that yachts who have their sails set for a breeze coming from the left hand side of the boat (the port side) must give way to yachts that have their sails set for a breeze coming from the opposite side of the boat (the starboard side). If both yachts have their sails set on the same side of the boat, then the yacht closer to where the wind is coming from must give way. This rule is described as the windward boat must keep clear of the leeward boat.

However there are many other rules besides and sailors are expected to know the essentials of boating safety which include;

The rules of the road or International Regulations for Preventing Collisions at Sea set forth by the International Maritime Organization are particularly relevant to sailors because of their limited maneuverability compared to powered vessels.
The IALA International Association of Lighthouse Authorities standards for lateral marks, lights, signals, and buoyage and various rules designed to support safe navigation.
The SOLAS (Safety of Life at Sea) regulations place the obligations for safety on the owners and operators of any boat. These regulations specify the safety equipment needed and emergency procedures to be used.

Sailing traditions and etiquette

There are many, more esoteric, etiquette rules, traditions, and customs that will demonstrate to others advanced knowledge of boating protocol. Fenders should be pulled up outside ports, the flag of the host country should be shown, flags are to taken down at night, one should not walk on other's forecastle, no whistling aboard etc.

Sail

A sail is a surface intended to generate thrust by being placed in a wind; basically it is a vertically oriented wing. Depending on the incident angle of the wind on the surface of the sail, one side of the sail will have a higher air pressure than the other one according to Bernoulli's principle. The difference in pressure will generate lift, causing the sail to be pulled towards the side of lower pressure. On a sailing boat, a keel or centreboard is used to convert this lateral force into forward movement of the boat with some sideways leaning, or 'heel'.

Use of sails

Sails are primarily used at sea, on sailing ships as a propulsion system. For purposes of commerce, sails have been largely superseded by other forms of propulsion, such as the internal combustion engine. For recreation, however, sailing vessels remain popular.

The most familiar type of sailboat, a small pleasure yacht, usually has a sail-plan called a sloop. This has two fore-and-aft sails: the mainsail and the jib.

The mainsail extends aftward and is secured the whole length of its edges to the mast and to a boom also hung from the mast. The sails of tall ships are attached to wooden timbers or "spars".

The jib is secured along its luff to a forestay (strong wire) strung from the top of the mast to the bowsprit on the bow (nose) of the boat. A genoa is also used on some boats. It is a type of jib that is larger, and cut so that it is fuller than an ordinary jib.

Fore-and-aft sails can be switched from one side of the boat to the other, in order to alter the boat's course. When the boat's stern crosses the wind, this is called jibing; when the bow crosses the wind, it is called tacking. Tacking repeatedly from port to starboard and/or vice versa, called "beating", is done in order to allow the boat to follow a course into the wind.

A primary feature of a properly designed sail is an amount of "draft", caused by curvature of the surface of the sail. When the sail is oriented into the wind, this curvature induces lift, much like the wing of an airplane. Modern sails are manufactured with a combination of broadseaming and non-stretch fabric (ref New technology below). The former adds draft, while the latter allows the sail to keep a constant shape as the wind pressure increases. The draft of the sail can be reduced in stronger winds by use of a cunningham and increasing the downward pressure of the boom.

Sail construction is governed by the science of aerodynamics

Parts of the Sail

The lower edge of a triangular sail is called the "foot" of the sail, while the upper point is known as the "head". The halyard, a line which raises the sail, is attached to the head. The lower two points of the sail, on either end of the foot, are called the "tack" (forward) and "clew" (aft). The tack is shackled to a fixed point on the boat such as the gooseneck in the case of a mainsail or the deck at the base of a stay in the case of a jib or staysail. The clew is movable and is positioned with running rigging, an outhaul on the mainsail and a sheet for a headsail.

The forward edge of the sail is called the "luff", from which derives the term "luffing", a rippling of the sail when the angle of the wind fails to maintain a good aerodynamic shape near the luff. The aft edge of a sail is called the "leech". If incorrectly tensioned, the leech of a sail may "flutter" noisily.

Modern sails are designed such that the warp and the weft of the sailcloth are oriented parallel to the luff and foot of the sail. This places the most stretchable axis of the cloth along the diagonal axis (parallel to the leech), and makes it possible for sailors to reduce the draft of the sail by tensioning the sail, mast and boom in various ways. A cunningham may be rigged on the mainsail to control sail shape.

An alternative approach to sail design is that used in Junks, originally an oriental design. It uses horizontal sail curving to produce an efficient and easily controlled sail-plan.

New technology

Sail producers are competing hard with the latest technology to produce the best, i.e. the most efficient sail: North sails with their 3DL sail, Doyle the 4D and Elvström Sobstad the Genesis sail. These sails are produced with carbon fibers and are glued/baked, compared to the old sewed cotton sails.

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