How sailing works

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.

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. 

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

What is Seamanship ?

Seamanship is the art of operating a ship or boat. It involves topics and development of specialised skills including: navigation and international maritime law; weather, meteorology and forecasting; watch keeping, ship-handling and small boat handling; operation of deck equipment, anchors and cables; rope work and line handling; communications; sailing; engines; execution of evolutions such as towing; cargo handling equipment, dangerous cargoes and cargo storage; dealing with emergencies; survival at sea and search and rescue; fire fighting.

The degree of knowledge needed within these areas is dependent upon the nature of the work and the type of vessel employed by a mariner. However, the practice of good seamanship should be the goal of all. The deep meaning of the word seamanship derives from the word seaman & ship. Thus it is the seaman who makes a good ship through his qualifications. Above all, Seamanship means Safety onboard and this is managed through continuous training and implementation of good working practices.

Often Seamanship is described as nothing but common sense.

Quarter gallery

A quarter gallery is an architectural feature of the stern of a sailing ship from  around the 16th to 19th century. Quarter galleries are a kind of balcony, typically placed on the side of the stern castle. A high, tower-like structure at the back of a ship that housed the officer's quarters. They function as a firing platform for the ship's marines and sharpshooters during boarding actions. The galleries also provided a structure that was ideally suited for attaching decoration and often bore carved wooden sculptures.

Captain's Mast

The "Captain's Mast" is a disciplinary event hailing from the age of sail where a ship's captain and other officers publicly shame and sentence sailors who have broken some rule in a manner severe enough to warrant public discipline but not enough to require a full legal proceeding. 

Before steam engines became standard in the nineteenth century the most efficient means of moving a ship across the sea was to harness the power of the wind by means of attaching a canvas sail to a wooden pole known as the mast. Larger ships would have several masts, and the number of masts as well as their configuration and the shapes of their many sails came to define the types of the various sailing ships, from the clipper to the man-o-war.

Sailor's lives depended on the function of these masts and sails, and much of the maintenance work needed to keep ships in working order involved these essential components of period vessels. It is no surprise then that they came to be a focal point of naval culture and a convenient meeting place for the crew when one was needed.

Under the Mainmast - Ceremonies for the Crew

The Captain's Mast appears to have come about as a result of the need to maintain discipline and to address the majority of the crew at once. Meetings of this nature were held under the mainmast, and eventually any crew meeting came to be known as a mast. The masts eventually began to be named according to the officiating officer's rank, and so there are admiral's masts and chaplain's masts.

The Captain's version was traditionally held prior to religious services and served as both a disciplinary event in front of the entire crew and as a forum where exemplary behavior could be praised or official news shared with the crew. Once it became so common to be held as a tradition, even as the vessels switched from sail to steam power the event was still held in a convenient meeting area, and given the same name.

How submarine work

A submarine or a ship can float because the weight of water that it displaces is equal to the­ weight of the ship. This displacement of water creates an upward force called the buoyant force and acts opposite to gravity, which would pull the ship down. Unlike a ship, a submarine can control its buoyancy, thus allowing it to sink and surface at will.

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air (see animation below). When the submarine is on the surface, the ballast tanks are filled with air and the submarine's overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks. In addition, the submarine has movable sets of short "wings" called hydroplanes on the stern (back) that help to control the angle of the dive. The hydroplanes are angled so that water moves over the stern, which forces the stern upward; therefore, the submarine is angled downward.

To keep the submarine level at any set depth, the submarine maintains a balance of air and water in the trim tanks so that its overall density is equal to the surrounding water (neutral buoyancy). When the submarine reaches its cruising depth, the hydroplanes are leveled so that the submarine travels level through the water. Water is also forced between the bow and stern trim tanks to keep the sub level. The submarine can steer in the water by using the tail rudder to turn starboard (right) or port (left) and the hydroplanes to control the fore-aft angle of the submarine. In addition, some submarines are equipped with a retractable secondary propulsion motor that can swivel 360 degrees.

When the submarine surfaces, compressed air flows from the air flasks into the ballast tanks and the water is forced out of the submarine until its overall density is less than the surrounding water (positive buoyancy) and the submarine rises. The hydroplanes are angled so that water moves up over the stern, which forces the stern downward; therefore, the submarine is angled upward. In an emergency, the ballast tanks can be filled quickly with high-pressure air to take the submarine to the surface very rapidly.

Port holes

The word "port hole" originated during the reign of Henry VI of England (1485). King Henry insisted on mounting guns too large for his ship and the traditional methods of securing these weapons on the forecastle and aftcastle could not be used.

A French shipbuilder named James Baker was commissioned to solve the problem. He put small doors in the side of the ship and mounted the cannon inside the ship. These doors protected the cannon from weather and were opened when the cannon were to be used. The French word for "door" is "porte" which was later Anglicized to "port" and later went on to mean any opening in the ship's side, whether for cannon or not.

Mediterranean Mooring

In some harbours where there is sufficient room to berth many ships alongside, ships may be obliged to berth at right-angles to a jetty, with their sterns secured to it by berthing lines and their anchors(s) laid out ahead.

This type of mooring can only be employed where there is a negligible range of tide, and is commonly used in Mediterranean ports; for this reason it is often called the Mediterranean (or Med) moor. 

The major considerations are to veer sufficient cable so that the ship can swing clear of other ships at the berth when leaving, to lay the anchors sufficiently far apart to make the ship more secure in wind, and to ensure the anchors do not foul those of other ships. 

In a shallow harbour it is recommended that a frigate veers about 4 shackles of cable on each anchor, and that cables are spanned with and included angle of about 50 degrees, so as to make the ship more secure in a wind. It is obvious, however, that to berth will not be safe if a gale blows from abeam.

If such weather is forecast it is advisable to put to sea or seek a sheltered anchor berth. Ships fitter with a single anchor can, in theory, carry out a Med moor; however, the single anchor will hold the bows steady only in benign weather conditions.