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Try this link for an Introduction to vectors. Note that nowhere in this argument did we need to say that the wind was faster than the boat. Now this force is mainly sideways on the boat, and it gets more and more sideways as you get closer to the wind.
However, part of the force is forward: the direction we want to go. Why doesn't the boat drift sideways? Well it does a little, but when it does, the keel , a large nearly flat area under the boat, has to push a lot of water sideways. The water resists this, and exerts the sideways force F k on the keel. This cancels the sideways component of F w. A little digression: the sideways components of wind and water on the boat make the boat heel tilt away from the wind, as is shown in the diagram below.
These two horizontal components have equal size but opposite direction: as forces they cancel, but they make a torque tending to rotate the boat clockwise. This is cancelled by another pair of forces. The buoyancy and the weight are also equal and opposite, and they make a torque in the opposite direction. As the boat heels to starboard, the lead on the bottom of the keel, which has a substantial fraction of the weight, moves to port and exerts an anticlockwise torque.
These two torques cancel. So now back to our question:. Lots of boats can � especially the eighteen footer skiffs on Sydney Harbour. Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities. Downwind diagram at left is easy. If the wind is 10 kt, and the boat makes 6 kt in the same direction, then the crew feels a wind of 4 kt coming over the stern of the boat.
The true wind v w equals the speed of the boat v b plus the relative wind v r. So you can't go faster than the wind. When the wind is at an angle, we have to add the arrows representing these velocities vector addition. The faster that the boat goes, the greater the relative wind, the more force there is on the sails, so the greater the force dragging the boat forwards.
So the boat accelerates until the drag from the water balances the forward component of the force from the sails. Why are eighteen footers always sailing upwind? In a fast boat, there's no point going straight downwind: you can never go faster than the wind. So you travel at an angle. But if your boat is fast enough, then the relative wind always seems to be coming mainly from ahead of you, as these arrows show. So the eighteen footers never set ordinary spinnakers: they have asymmetrical sails that they can set even when they are travelling at small angles to the apparent wind.
A good list of links to technical material , courtesy of Sailboat Technology. How can you trim the mainsail using blocks and pulleys to multiply your force?
More about hull shapes, bouyancy and sails. Australian Marine Services Directory has links to weather services, marine services and other information. Coriolis forces and the reasons behind the major ocean currents and winds.
Another puzzle involving relative motion of the air: the plane on the conveyor belt. Did you know that both the special and general theories of relativity are important in the Global Positioning System? See this link from Univ. See where the satellites are at the moment in this animation from J-Track.
Details at Science Outreach Centre news and Activities for students and teachers. Answer to puzzle. The faster heat is the one with no wind. When the wind and the water both move W to E at 10 kt, the boats drift down the river at 10 kt, with their sails hanging limp.
In the heat with no wind as measured on the land , a drifting boat has a headwind of 10 kt. When sailing craft are on a course where the angle between the sail and the apparent wind the angle of attack exceeds the point of maximum lift, separation of flow occurs. In addition to the sails used upwind, spinnakers provide area and curvature appropriate for sailing with separated flow on downwind points of sail, analogous to parachutes, which provide both lift and drag.
Spinnaker cross-section trimmed for a broad reach showing transition from the boundary layer to separated flow where vortex shedding commences. Wind speed increases with height above the surface; at the same time, wind speed may vary over short periods of time as gusts.
Wind shear affects sailing craft in motion by presenting a different wind speed and direction at different heights along the mast. Wind shear occurs because of friction above a water surface slowing the flow of air. Additionally, apparent wind direction moves aft with height above water, Boat Sailing Close To The Wind 3d which may necessitate a corresponding twist in the shape of the sail to achieve attached flow with height.
Gusts may be predicted by the same value that serves as an exponent for wind shear, serving as a gust factor. So, one can expect gusts to be about 1. This, combined with changes in wind direction suggest the degree to which a sailing craft must adjust sail angle to wind gusts on a given course.
A sailing craft's ability to derive power from the wind depends on the point of sail it is on�the direction of travel under sail in relation to the true wind direction over the surface. In points of sail that range from close-hauled to a broad reach, sails act substantially like a wing, with lift predominantly propelling the craft.
In points of sail from a broad reach to down wind, sails act substantially like a parachute, with drag predominantly propelling the craft. For craft with little forward resistance ice boats and land yachts , this transition occurs further off the wind than for sailboats and sailing ships. Wind direction for points of sail always refers to the true wind �the wind felt by a stationary observer. The apparent wind �the wind felt by an observer on a moving sailing craft�determines the motive power for sailing craft.
The waves give an indication of the true wind direction. The pennant Canadian flag gives an indication of apparent wind direction. Reaching : the pennant is streaming slightly to the side as the sails are sheeted to align with the apparent wind.
Running : the wind is coming from behind the vessel; the sails are "wing and wing" to be at right angles to the apparent wind. True wind velocity V T combines with the sailing craft's velocity V B to be the apparent wind velocity V A , the air velocity experienced by instrumentation or crew on a moving sailing craft.
Apparent wind velocity provides the motive power for the sails on any given point of sail. It varies from being the true wind velocity of a stopped craft in irons in the no-go zone to being faster than the true wind speed as the sailing craft's velocity adds to the true windspeed on a reach, to diminishing towards zero, as a sailing craft sails dead downwind.
Sailing craft A is close-hauled. Sailing craft B is on a beam reach. Sailing craft C is on a broad reach. Boat velocity in black generates an equal and opposite apparent wind component not shown , which adds to the true wind to become apparent wind.
Apparent wind and forces on a sailboat. As the boat sails further from the wind, the apparent wind becomes smaller and the lateral component becomes less; boat speed is highest on the beam reach.
Apparent wind on an iceboat. As the iceboat sails further from the wind, the apparent wind increases slightly and the boat speed is highest on the broad reach. The sail is sheeted in for all three points of sail. The speed of sailboats through the water is limited by the resistance that results from hull drag in the water. Ice boats typically have the least resistance to forward motion of any sailing craft.
On conventional sailboats, the sails are set to create lift for those points of sail where it's possible to align the leading edge of the sail with the apparent wind. For a sailboat, point of sail affects lateral force significantly. The higher the boat points to the wind under sail, the stronger the lateral force, which requires resistance from a keel or other underwater foils, including daggerboard, centerboard, skeg, and rudder.
Lateral force also induces heeling in a sailboat, which requires resistance by weight of ballast from the crew or the boat itself and by the shape of the boat, especially with a catamaran. As the boat points off the wind, lateral force and the forces required to resist it become less important. Wind and currents are important factors to plan on for both offshore and inshore sailing.
Predicting the availability, strength and direction of the wind is key to using its power along the desired course. Ocean currents, tides and river currents may deflect a sailing vessel from its desired course. If the desired course is within the no-go zone, then the sailing craft must follow a zig-zag route into the wind to reach its waypoint or destination.
Downwind, certain high-performance sailing craft can reach the destination more quickly by following a zig-zag route on a series of broad reaches. Negotiating obstructions or a channel may also require a change of direction with respect to the wind, necessitating changing of tack with the wind on the opposite side of the craft, from before. Changing tack is called tacking when the wind crosses over the bow of the craft as it turns and jibing or gybing if the wind passes over the stern.
Winds and oceanic currents are both the result of the sun powering their respective fluid media. Wind powers the sailing craft and the ocean bears the craft on its course, as currents may alter the course of a sailing vessel on the ocean or a river. A sailing craft can sail on a course anywhere outside of its no-go zone. Because the lateral wind forces are highest on a sailing vessel, close-hauled and beating to windward, the resisting water forces around the vessel's keel, centerboard, rudder and other foils is also highest to mitigate leeway �the vessel sliding to leeward of its course.
Ice boats and land yachts minimize lateral motion with sidewise resistance from their blades or wheels. Tacking from starboard tack to port tack. Wind shown in red. Beating to windward with tacking points shown from starboard to port tack at points 1. Tacking or coming about is a maneuver by which a sailing craft turns its bow into and through the wind called the "eye of the wind" so that the apparent wind changes from one side to the other, allowing progress on the opposite tack.
Fore-and-aft rigs allow their sails to hang limp as they tack; square rigs must present the full frontal area of the sail to the wind, when changing from side to side; and windsurfers have flexibly pivoting and fully rotating masts that get flipped from side to side. A sailing craft can travel directly downwind only at a speed that is less than the wind speed.
However, a variety of sailing craft can achieve a higher downwind velocity made good by traveling on a series of broad reaches, punctuated by jibes in between. This is true of iceboats and sand yachts. On the water it was explored by sailing vessels, starting in , and now extends to high-performance skiffs, catamarans and foiling sailboats.
Navigating a channel or a downwind course among obstructions may necessitate changes in direction that require a change of tack, accomplished with a jibe. Jibing or gybing is a sailing maneuver by which a sailing craft turns its stern past the eye of the wind so that the apparent wind changes from one side to the other, allowing progress on the opposite tack.
This maneuver can be done on smaller boats by pulling the tiller towards yourself the opposite side of the sail. Fore-and-aft sails with booms, gaffs, or sprits are unstable when the free endpoints into the eye of the wind and must be controlled to avoid a violent change to the other side; square rigs as they present the full area of the sail to the wind from the rear experience little change of operation from one tack to the other; and windsurfers again have flexibly pivoting and fully rotating masts that get flipped from side to side.
The most basic control of the sail consists of setting its angle relative to the wind. The control line that accomplishes this is called a "sheet. Finer controls adjust the overall shape of the sail. Two or more sails are frequently combined to maximize 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. 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 means reducing the area of a sail without actually changing it for a smaller sail. Ideally, reefing does not only result in a reduced sail area but also in a lower centre of effort from the sails, reducing the heeling moment and keeping the boat more upright.
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. An old saying goes, "Once you've realized it's time to reef, it's too late". A similar one says, "The time to reef is when you first think about it".
Hull trim is the adjustment of a boat's loading so as to change its fore-and-aft attitude in the water. In small boats, it is done by positioning the crew. In larger boats, the weight of a person has less effect on the hull trim, but it can be adjusted by shifting gear, fuel, water, or supplies. Different hull trim efforts are required for different kinds of boats and different conditions. Here are just a few examples: In a lightweight racing dinghy like a Thistle , the hull should be kept level, on its designed water line for best performance in all conditions.
In many small boats, weight too far aft can cause drag by submerging the transom , especially in light to moderate winds. Weight too far forward can cause the bow to dig into the waves.
In heavy winds, a boat with its bow too low may capsize by pitching forward over its bow pitch-pole or dive under the waves submarine. On a run in heavy winds, the forces on the sails tend to drive a boat's bow down, so the crew weight is moved far aft.
When a ship or boat leans over to one side, from the action of waves or from the centrifugal force of a turn or under wind pressure or from the number of exposed topsides, it is said to 'heel'.
A sailing boat that is over-canvassed , and therefore heeling excessively, may sail less efficiently. This is caused by factors such as wind gusts, crew ability, the point of sail, or hull size and design. When a vessel is subject to a heeling force such as wind pressure , vessel buoyancy and beam of the hull will counteract the heeling force.
A weighted keel provides additional means to right the boat. In some high-performance racing yachts, water ballast or the angle of a canting keel can be changed to provide additional righting force to counteract heeling. The crew may move their personal weight to the high upwind side of the boat, this is called hiking , which also changes the centre of gravity and produces a righting lever to reduce the degree of heeling.
Incidental benefits include faster vessel speed caused by more efficient action of the hull and sails. Other options to reduce heeling include reducing exposed sail area and efficiency of the sail setting and a variant of hiking called " trapezing ". This can only be done if the vessel is designed for this, as in dinghy sailing. A sailor can usually involuntarily try turning upwind in gusts it is known as rounding up.
This can lead to difficulties in controlling the vessel if over-canvassed. Wind can be spilled from the sails by 'sheeting out', or loosening them. The number of sails, their size, and shape can be altered. Raising the dinghy centreboard can reduce heeling by allowing more leeway.
The increasingly asymmetric underwater shape of the hull matching the increasing angle of heel may generate an increasing directional turning force into the wind. The sails' centre of effort will also increase this turning effect or force on the vessel's motion due to increasing lever effect with increased heeling which shows itself as increased human effort required to steer a straight course.
Increased heeling reduces exposed sail area relative to the wind direction, so leading to an equilibrium state. As more heeling force causes more heel, weather helm may be experienced. This condition has a braking effect on the vessel but has the safety effect in that an excessively hard pressed boat will try to turn into the wind, therefore, reducing the forces on the sail. This aerofoil lift produces helpful motion to windward and the corollary of the reason why lee helm is dangerous.
Lee helm, the opposite of weather helm, is generally considered to be dangerous because the vessel turns away from the wind when the helm is released, thus increasing forces on the sail at a time when the helmsperson is not in control.
In the case of a standard catamaran , there are two similarly-sized and -shaped slender hulls connected by beams, which are sometimes overlaid 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 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 lesser draft reduces the amount of drag, caused by friction and inertia when moving through the water.
One of the most common dinghy hulls in the world is the Laser hull. It was designed by Bruce Kirby in and unveiled at the New York boat show It was designed with speed and simplicity in mind. The Laser is 13 ft Nautical terms for elements of a vessel: starboard right-hand side , port or larboard left-hand side , forward or fore frontward , aft or abaft rearward , bow forward part of the hull , stern aft part of the hull , beam the widest part.
Spars, supporting sails, include masts, booms, yards, gaffs and poles. In most cases, rope is the term used only for raw material. Once a section of rope is designated for a particular purpose on a vessel, it generally is called a line, as in outhaul line or dock line. A very thick line is considered a cable. Lines that are attached to sails to control their shapes are called sheets , as in mainsheet. If a rope is made of wire, it maintains its rope name as in 'wire rope' halyard.
Lines generally steel cables that support masts are stationary and are collectively known as a vessel's standing rigging , and individually as shrouds or stays. The stay running forward from a mast to the bow is called the forestay or headstay. Stays running aft are backstays or after stays. Moveable lines that control sails or other equipment are known collectively as a vessel's running rigging.
Lines that raise sails are called halyards while those that strike them are called downhauls. Lines that adjust trim the sails are called sheets. These are often referred to using the name of the sail they control such as main sheet or jib sheet. Sail trim may also be controlled with smaller lines attached to the forward section of a boom such as a cunningham; a line used to hold the boom down is called a vang , or a kicker in the United Kingdom.
A topping lift is used to hold a boom up in the absence of sail tension. Guys are used to control the ends of other spars such as spinnaker poles. Lines used to tie a boat up when alongside are called docklines , docking cables or mooring warps.
In dinghies, the single line from the bow is referred to as the painter. A rode is what attaches an anchored boat to its anchor. It may be made of chain, rope, or a combination of the two. Walls are called bulkheads or ceilings , while the surfaces referred to as ceilings on land are called overheads or deckheads.
Floors are called soles or decks. The toilet is traditionally called the head , the kitchen is the galley. When lines are tied off, this may be referred to as made fast or belayed.
Sails in different sail plans have unchanging names, however. For the naming of sails, see sail-plan. The following knots are regarded as integral to handling ropes and lines, while sailing: [36] [37]. Lines and halyards are typically coiled neatly for stowage and reuse. In some sailing events, such as the Olympic Games , which are held on closed courses where no other boating is allowed, specific racing rules such as the Racing Rules of Sailing RRS may apply.
The stand-on vessel must hold a steady course and speed but be prepared to take late avoiding action to prevent an actual collision if the other vessel does not do so in time.
The give-way vessel must take early, positive and obvious avoiding action, without crossing ahead of the other vessel. Rules 16� Specifically, for sailing boats, red and green sidelights and a white stern light are required, although, for vessels under 7 m 23 ft in length, these may be substituted by a torch or white all-round lantern.
Sailors are required to be aware not only of the requirements for their own boat but of all the other lights, shapes, and flags that may be shown by other vessels, such as those fishing, towing, dredging, diving, etc. Rules 32� Licensing regulations vary widely across the world. While boating on international waters does not require any license, a license may be required to operate a vessel on coastal waters or inland waters.
Some jurisdictions require a Boat Sailing Close To The Wind Of Change license when a certain size is exceeded e. For example, the European Union issues the International Certificate of Competence , which is required to operate pleasure craft in most inland waterways within the union.
The United States , in contrast, has no licensing, but instead has voluntary certification organizations such as the American Sailing Association.
Sailboat racing generally fits into one of two categories:. Sailing is a diverse sport with many pinnacles from the Olympic Games to many world championships titles to development based campaigns for the America's Cup to round the world races such as the Vendee Globe and Volvo Ocean Race. Sailboat racing ranges from single-person dinghy racing to large boats with 10 or more crew and from small boats costing a few thousand dollars to multimillion-dollar America's Cup campaigns.
The costs of participating in the high-end large boat competitions make this type of sailing one of the most expensive sports in the world. However, there are inexpensive ways to get involved in sailboat racing, such as at community sailing clubs, classes offered by local recreation organizations and in some inexpensive dinghy and small catamaran classes. Under these conditions, sailboat racing can be comparable to or less expensive than sports such as golf and skiing.
Sailboat racing is one of the few sports in which people of all ages and genders can regularly compete with and against each other.
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