Sailing
Sailing is the use of wind to move an object.
Usually "sailing" is associated with moving a boat or ship on water. But there are other kinds of sailing, including
- ice sailing
- land sailing (on large flat areas) and
- para sailing (when a person on a board is on and/or above ocean surf).
The focus of this article is moving a boat or a ship across water.
In the past, sailing was the most common method of moving ships. Nowadays, sailing is most commonly used to move boats only. So, this article usually comments upon boats. But the principles which apply to boats equally apply to ships.
(There are numerous opinions of what the differences are between a ship and a boat. Bowditch states a ship was "originally a sailing vessel with three or more masts, square-rigged on all".)
Purpose
The original purpose of sailing was to provide transport of goods or people. Water transport was often easier and faster than land transport because there were few roads, and the only mode of land transport was walking or using animals. In some cases, water transport was the only option because two places were separated by water.
In the last few hundred years, sailing has been increasingly undertaken for pleasure. This can be in the form of sailing races, or just "cruising" for the day or much longer. Sailing is even one of the Olympic sports.
There are still parts of the world where sailing is still the only or the best form of transport.
History
Humans have been sailing for thousands of years. No one knows when someone first sailed, but it is likely that sailing was developed in several parts of the world independently.
Rigging types
Cat rig
Sloop
Lanteen rig
Fore-and-aft rig
Identified by sails which are approximately triangles. The luff (forward edge) of a fore-and-aft sail is usually attached to the mast and its foot (bottom edge) is usually attached to a boom. But there are variations to this design.
Sometimes a vessel powered exclusively by engine will put up a fore and aft "steading sail" to reduce the amount of roll caused by rough seas. As this sail does not move the vessel, it is not considered a sailing vessel and is not a "fore-and-aft rig".
Square-rig
Identified by sails which are approximately rectangles. The boom of a rectangular sail is above the sail.
Large European sailing vessels were usually square-rigged.
Square-rigged sails can not be used to sail toward the wind. (See the Physics section for an explanation why.)
Some vessels have both rectangular and triangular sails. Some of these triangular sails might be connected to a mast and/or boom and provide propulsion to the vessel. Some triangular sails might be performing a function similar to a jib, of directing wind so another sail can provide increase its efficiency. A vessel with both rectangular and triangular sails is usually still categorised as "square-rigged".
Multi-masted
There is specific nomenclature for masts, sails and booms on multi-masted vessels.
Two masts, forward mast taller; this is called a "ketch" or a "yawl"
- "main mast" is forward
- "mizzen mast" is aft
Two masts, aft mast the same height or taller; this is called a "schooner"
- "fore mast" is forward
- "main mast" is aft
Three masts, provided the aft mast is not taller than the others
- "fore mast" is forward
- "main mast" is in the middle
- "mizzen mast" is aft
There are no hard and fast rules when there are four or more masts. For example, a seven-masted vessel named its masts "Monday" through "Sunday".
Hull types
Sailboats can be monohulls (a single hull), catamarans (two hulls) or trimarans (three hulls). Each type of hull has its advantages and disadvantages.
A monohull
- heels more than a multi-hull when there is a wind gust (which is a good release of excess wind)
- a large monohull usually needs to have a heavy keel to reduce the likelihood of capsizing
- is able to sail more directly toward the wind than a multi-hull
- has a lower maximum hull speed than a catamaran of equal length
A catamaran
- heels less than a mono-hull when there is a wind gust (which requires more attention to ensure there is a release of excess wind)
- is not as able to sail as close to the wind as a monohull
- has a higher maximum hull speed than a monohull of equal length
- because it does not have a heavy keel and therefore is lighter than a monohull of equal volume, it usually requires smaller mast, sail and rigging
Physics
Most simply, sailing uses the difference in air pressure between the two sides of a sail as mechanical energy to move a boat.
A square sail has wind blowing against its "back" side, causing greater pressure on the back of the sail than the front of the sail. As a result, the sail attempts to move away from the greater pressure to the lower pressure. This force is transmitted to the boom, then the mast, then the hull, resulting in the boat moving.
The same principle applies when the wind is blowing against one side of a fore & aft sail.
(The "back" side of a sail might not be facing directly toward the back of the boat if its boom and sheet(s) place the sail on an angle to the boat.)
It is a little more complicated when the wind is blowing across both sides of a fore & aft sail. We are still using the difference in air pressure of the two sides of the sail to produce mechanical energy. The way the difference in air pressure is created on a sail is identical to the way differences in air pressure are created between the upper and lower sides of an aircraft wing, resulting in lift to make an airplane fly.
The diagram to the right is an example of what a fore-and-aft sail might look like while sailing. The wind approaches the sail from the direction of "A". The wind which goes on the outside of the curve to point "B" has further to go than the wind which goes on the inside of the curve to point "B". The wind which must go further must therefore travel faster. This increased results in a decrease of pressure. As a result, there is a pressure difference between the two sides of the sail.
Click on this image for details.
As a result, the sail attempts to move away from the greater pressure to the lower pressure. This force is transmitted to the boom and/or mast, then the hull, resulting in the boat moving. Since the force is not directly toward the bow of the boat, the boat will have a tendency to slide sideways in the water. To reduce the amount that this happens, a small boat often has a centerboard and a larger boat tends to have a keel which extends down.
Sometimes one or more jibs are used to speed up the air flow around the curved edge of the sail. This increases the pressure difference, which therefore increases the speed of the boat.
Points of sail
"Points of sail" indicates the direction from which the wind is coming.
No boat can sail directly into the wind. The design of the hull(s), mast(s) and sail(s) determine how "close" to the wind a sailing vessel can sail. One is said to be "close" to the wind when sailing almost directly toward the wind.
There are no universally-agreed definitions where one "point of sail" ends and another begins. The points of sail are
- close hauled
- the vessel is sailing as close to the wind as it can
- close reach
- between close hauled and a beam reach
- beam reach
- the wind is abeam, or nearly so
- broad reach
- the wind is coming from the quarter (approximately 45 degrees from astern)
- run (or running free)
- the wind is directly aft, or nearly so
"Close hauled" and "close reach" directions might vary significantly between boats, as one might be able to sail 30 degrees off the wind close hauled while another might not be able to sail any closer than 45 or 60 degrees off the wind.
Trimming
Trimming is probably the most difficult aspect of sailing. Trimming is so complex it can probably be an entire article in itself.
When trimming a sailboat, one must balance many considerations, including
- the destination one is attempting to arrive at
- the direction of the wind
- the strength of the wind and
- whether the crew's mass is to be used to "flatten" the boat so the boat can be trimmed in a way which will make it travel faster.
Basically, the intent of trimming is to set the sail at a point to maximise motion toward one's destination.
Just because a sailboat will make headway when pointing the boat towards its destination does not mean it is the best trim for the boat. This is because
- a sailboat almost always moves sideways as well as forward, so the boat will not reach its destination just because it is pointed toward it and
- sometimes falling off a few degrees can greatly increase boat speed. If this is the case, the boat might arrive at its destination faster by falling off a bit and tacking a couple of times.
In general, if the destination is not directly (or almost directly) toward the wind, aim the boat a little to windward of the destination. Then pull in the mainsail sheet until the sail has a good curve to it. That should be the best trim. If the sail has a jib, pull in its sheet, to just before the flow of the jib's air starts to cause some flapping in the curve of the mainsail.
Some sails have "telltails" in order to observe the flow of air over the sail. An indication of good trim is when telltails are near horizontal and flapping little.
Trimming a square-rigged vessel is even more complex than trimming a fore-and-aft vessel.
Sailing as a sport
The sport of sailing is undertaken by children, elderly adults and all ages between.
Sailing as a sport can be a race of less than an hour on a calm harbour or lake in a boat as small as two metres (about six and a half feet) or a race of several months around-the-world in a boat tens of metres long.
Sailing is one of the summer Olympic sports.
Race classes
Sailing race classes are defined hull designs and/or sail designs. One reason for having precisely-defined classes is so that a sailing race is more likely to be a contest of the skills of the sailors to sail rather than a competition of their ability to raise money, their design skill or their construction skill.
Longer races, such as the Sydney-to-Hobart race or an around-the-world race are likely to include boats of many classes. The boats must all meet minimum safety and other standards, but are likely to have a wide variation in hull size, hull design and sail design.
In such races, one can obtain 'line honours' by being amongst the first to complete the race, but one can also win by 'handicap'. There might also be winners for various boat sizes or types; these categories vary between races.
Sailing handicaps
Handicaps are an attempt to take into account the differences in hull size, hull design and sail design so that the best sailor (rather than the biggest or best boat) wins by handicap.
Racing strategies
Racing strategies can include
- starting-line strategies
- using the correct sail for the correct condition
- sailing in the correct location to catch wind others do not
- sailing in the correct location to use current others do not and
- using a myriad of other factors, depending upon the race.
Sailing as a lifestyle
Some people buy sailboats to be their homes. Some raise their children on their boats.
Some of them have full-time jobs, and some do not.
Some stay in one place and only wander on weekends and holidays, and some are always wandering. "Cruising" is the expression used when someone wanders while living aboard their sailboat.
Organisations
There are sailing organisations in almost every country, even when land-locked.
Some are dedicated to a specific class of sailboat. Some have a broader charter.