A well designed spinnaker will have taut leading edges when filled; leading edges that curl in will both reduce the lift and risk a collapse of the spinnaker. A well designed spinnaker will also have a smooth curve when filled, with no bubbles or depressions caused by inconsistent stretching of the sail fabric. Any deviations from a smooth curve will cause the airflow over the leeward side of the sail to separate, in a reaching spinnaker, causing a reduction in lift and reduced performance.
When running downwind in heavy weather or when hit by a gust, with or without a spinnaker, there may be a tendency for a roll of increasing amplitude to build up, known as the death roll. It has been shown that this is due to aerodynamic instability of bermuda rigs when running, which can be aggravated by gusts, waves, mainsail twist, daggerboard etc too far down, hull form, and the sailing equivalent of pilot-induced oscillation. Excessive heel leads to loss of rudder effectiveness resulting in the boat slewing round uncontrollably in the direction opposite to the direction of heel. This is known as broaching. Aerodynamic instability when running can be countered by easing the pole forward slightly and over-sheeting the spinnaker somewhat to stop it swinging from side to side, by reducing mainsail twist using the boom vang, and by skillfully trimming the mainsheet. Luffing carefully onto a broad reach may help to retain control, as can moving everyone's weight as far aft as possible. Reducing sail should be considered.
The symmetric one is the most classic type, running symmetrical alongside the boat controlled by lines known as a sheet and a guy running from the lower two corners of the sail. The windward line, or guy, is attached to the corner called the tack of the sail, and is stabilized by a spinnaker pole. The leeward (downwind) line is called the sheet. It attaches to the clew of the spinnaker and is used to control the shape of the sail. The spinnaker pole must be moved in each gybe, and is quite difficult for beginners to use. However, it can be sailed in all downwind wind directions.
Symmetric spinnakers when sailing across the wind (reaching) develop most of their lift on the forward quarter, where the airflow remains attached. When correctly set for reaching, the leading edges of a symmetric spinnaker should be nearly parallel to the wind, so the flow of air over the leading edge remains attached. When reaching, the sail camber allows only some attached flow over the leeward side of the spinnaker. On running the spinnaker is angled for maximum drag, with the spinnaker pole at right angles to the apparent wind. The symmetric spinnaker also requires care when packing, since the three corners must be available on the top of the packing.
Asymmetric spinnakers resembling large jibs and flown from spinnaker poles are not a new idea and date back to at least the 19th Century. However in the 1980s a new concept appeared, starting with the Sydney Harbour 18ft Skiff fleet. Since the 1960s many faster sailing craft, starting with catamaran classes, had discovered that it is faster to sail downwind on a series of broad reaches with efficient airflow across the sail rather than directly downwind with the sails stalled. This technique had developed to the extent that in bar conversation at the end of one season Andrew Buckland observed that the 18s had sailed all season without pulling the spinnaker pole back from the forestay and that all the systems could be simplified by eliminating the pole and setting the spinnaker from a fixed bowsprit. The concept quickly evolved to a sail with a loose luff much more like a conventional spinnaker than the old jib style asymmetric sails. Julian Bethwaite was the first to rig and sail a boat with one the next season, followed shortly by Andrew Buckland.
The concept has spread rapidly through the sailing world. The tack of the sail may be attached at the bow like a genoa but is frequently mounted on a bowsprit, often a retracting one. If the spinnaker is mounted to a special bowsprit, it is often possible to fly the spinnaker and the jib at the same time; if not, then the spinnaker will be shadowed by the jib, and the jib should be furled when the spinnaker is in use.
The asymmetric has two sheets, very much like a jib, but is not attached to the forestay along the length of the luff, but only at the corners. Unlike a spinnaker, the asymmetric does not require a spinnaker pole, since it is fixed to the bow or bowsprit. The asymmetric is very easy to jibe since it only requires releasing one sheet and pulling in the other one, passing the sail in front of the forestay. Asymmetrics are less suited to sailing directly downwind than spinnakers, and so instead the boat will often sail a zig-zag course downwind, gybing at the corners. An asymmetric spinnaker is particularly effective on fast planing dinghies as their speed generates an apparent wind on the bow allowing them to sail more directly downwind. It is also particularly useful in cruising yachts in the form of a cruising spinnaker or cruising chute, where the ease of handling is important. Various types of asymmetrics exist, and a common nomenclature classifies them by code from 0 to 6. Codes 1, 3, and 5 are reaching sails, and codes 2, 4, and 6 are running sails; the code 0 is a hybrid of genoa and spinnaker, designed to work like a genoa but classified under racing rules as a spinnaker.
Spinnakers for cruising boats are starting to be patterned after the roller furling code 0 racing spinnakers, as they provide the easiest handling. North Sails, for example, offers three gennaker sails, based on the racing code 0 asymmetrics, with different sizes and cambers for varying angles and wind speeds. Other manufacturers offer similar cruising code 0 designs under different names, such as the screecher and reacher for upwind and downwind use respectively.
The spinnaker pole may be allowed to raise and lower with the force of the wind, or it may have lines attached to it to raise (the topping lift) and lower (the foreguy) the angle of the pole. If these lines are used, they are generally set up before setting sail, and left in place even when the spinnaker is stowed.
Since symmetrics are downwind sails, they are never tacked, they are only jibed. When jibing a symmetric, the pole is moved to the bow, where the sail is detached, and the opposite corner attached. This corner now becomes the windward corner. The guys are adjusted as before to set the sail angle on the new course.
To retrieve the spinnaker, the windward corner is detached from the spinnaker pole, and the guy is released. This allows the spinnaker to collapse into the shadow of the mainsail, where the foot is gathered by a crewmember. The halyard is then lowered, and a crewmember gathers the sail and stuffs it carefully into the turtle, corners out, and ready for the next deployment.
Jibing with the asymmetric is much less complex than the symmetric, due to the lack of the spinnaker pole. Much like a jib, all that is required is to change guys--however, since the asymmetric still flies in front of the forestay, the operation is reversed. The sheet is slackened, and the opposite guy is pulled in, which allows the sail to pass around in front of the forestay, and then be sheeted in on the new lee side of the boat.
Retrieving the asymmetric is similar to the process for the symmetric. The guys are released, allowing the sail to collapse to the front of the boat. The foot of the sail is then gathered, and the halyard released and the head of the sail lowered, where it is packed into the turtle.
The spinnaker is raised as normal, but with the sock in place the spinnaker is unable to catch the wind. Once the spinnaker is raised and the guys are ready to set, the sock is raised, releasing the spinnaker. The sock remains bundled up at the head of the sail while the spinnaker is deployed. To retrieve the spinnaker, the sheet or the tack is released and the sock is pulled down, gathering the sail. The halyard is then dropped and the sail may be packed away.
If the spinnaker chute penetrates the hull and is required to be watertight, it takes the form of a hard tube sealed to the hull at both ends. If a watertight arrangement is not required, a cloth tube may be used to contain the lowered spinnaker.
Some dictionaries suggest that the origin of the word could be traced to the first boat to commonly fly a spinnaker, a yacht called the Sphinx, mispronounced as Spinx. The Sphinx first set her spinnaker in the Solent in 1865, and the first recorded use of the word was in 1866 in the August edition of Yachting Calendar and Review (p. 84). Some further claim that the friends of Sphinx's owner, Herbert C Maudslay of Seaview IoW, jokingly referred to the sail as "Sphinx's half-acre", and this was later to be abbreviated as spinnaker. In addition, the term may have been influenced by the spanker, originally a gaff rigged fore-and-aft sail.
It has been pointed out, however, that the skippers of the barges on the Thames (see Thames sailing barge) also used the term spinnaker for their jib staysails. Unlike the other, tanned sails of these boats, the spinnakers were usually of white color. It has thus been suggested that the term could be "connected with the obsolete word spoon, meaning to run before the wind (cf. spindrift). Early usage of the verb to spoon can be traced back to the 16th century; the change from spoon to spin in the term spindrift is attributed to a local Scottish pronunciation. According to Merriam Webster's dictionary, however, spindrift derives from a local Scottish pronunciation of speen (not spoon), meaning "to drive before a strong wind.
According to Merriam-Webster's dictionary, finally, the origin of the word spinnaker is simply unknown.