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[[Image:Tacking.svg|frame|Tacking from starboard tack to port tack. <big>&#x2460;</big> on [[starboard]] tack, <big>&#x2461;</big> turning to windward to begin the tacking maneuver or "preparing to come about", <big>&#x2462;</big> headed into the wind where [[momentum]] carries the vessel forward, <big>&#x2463;</big> powering up on the new port tack by sheeting in the mainsail, <big>&#x2464;</big> on [[port (nautical)|port]] tack.]]

==Era della navigazione==

'''Tacking''' or '''coming about''' is a [[sailing]] maneuver by which a sailing vessel (which is sailing into the wind) turns its [[bow (ship)|bow]] through the wind so that the direction from which the wind blows changes from one side to the other. For example, if a vessel is sailing on a [[starboard]] tack with the wind blowing from the right side and tacks, it will end up on a [[port (nautical)|port]] tack with the wind blowing from the left side. See the image at the right; the red arrow indicates the wind direction.

[[File:Uss iowa bb-61 pr.jpg|250px|thumb|Una bordata dalla[[USS Iowa (BB-61)|USS ''Iowa'']] (1984). Notevole lo spostamento d'acqua sotto i cannoni.]]

In practice, the sails are set at angle of 45° to the wind for conventional sailships and the tacking course is kept as short as possible before a new tack is set in. [[Rotor ship]]s can tack much closer to the wind, 20 to 30°.

Durante l'era della navigazione (e nei primi anni del [[Motore a vapore|vapore]]) le navi avevano lunghe file di cannoni nello stesso lato dello [[scafo]], i quali potevano sparare solo da un lato; il fuoco da tutte le armi su un lato della nave era conosciuto come ''bordata''; sparare da tutte le armi da entrambi i lati veniva chiamato ''bordata doppia''. I cannoni delle [[Man-of-war]] del [[XVIII secolo]] erano precisi solo a distanza ravvicinata, e il loro potere penetrante era mediocre, cosìcche gli scafi spessi delle navi di legno non potevano essere danneggiati, se non a distanze ravvicinate. Queste navi di legno navigavano avvicinandosi sempre di più l'una verso l'altra, fino a quando il fuoco dei cannoni sarebbe efficace. Ognuna delle navi cercava di essere la prima a sparare una bordata, ottenendo così un vantaggio decisivo nella battaglia<ref>Stephen Biesty (ill.) and Richard Platt (author). (1993). ''Stephen Biesty's Cross-Sections Man-of-War.'' New York: Dorling Kindersley.</ref>.

A similar maneuver (termed [[jibing]]) is used when sailing before the wind.

==La bordata come misura==

[[File:Hull model by Augustin Pic mp3h9729.jpg|150px|thumb|upright|Cannoni su un [[vascello]] francese a 74 cannoni.]]

Inoltre, il termine bordata è una misura della potenza massima simultanea di fuoco di una nave, che può essere scaricata su un unico obiettivo, in quanto questa concentrazione è di solito ottenibile sparando una bordata. Questa è calcolata moltiplicando il peso del proiettile dell'armamento principale della nave per il numero di barili che possono essere esercitati. Se alcune torrette non sono in grado di sparare da entrambi i lati della nave, sono contati solo il numero massimo di barili che possono sparare da una parte o dall'altra. Ad esempio, le [[Nave da battaglia|corazzate]] statunitensi [[USS Iowa (BB-61)|classe ''Iowa'']] trasportano un armamento principale di nove cannoni da 16 pollici, su torrette che possono essere regolate per una bordata unica. Ogni proiettile da 16 pollici pesa 2700 [[libbra|libbre]] (1224,7 [[chilogrammo|kg]] circa), che moltiplicato per nove (il numero totale di barili in tutte e tre le torrette) corrisponde a un totale di 24300 libbre (11022 kg). Così, una corazzata classe Iowa ha una bordata di 12 tonnellate corte (11,0 tonnellate), il peso dei proiettili che si può teoricamente indirizzare su un bersaglio in una singola bordata.

==Note==

<references/>

==Technical usage==

[[Image:beating_to_windward.svg|thumb|right|300px|Relationship between '''tacking''' and '''beating to windward''']]

Tacking is distinct from [[jibe|jibing]], where the ship's stern passes through the wind.

'''Tacking''' is sometimes confused with ''beating to windward'', which is a process of beating a course upwind and generally implies (but does not require) actually coming about. In the accompanying figure, the boat is seen to tack three times while beating to windward.

When used without a modifier, the term "tacking" is always synonymous with "coming about"; however, some find it acceptable to say "tack downwind"; i.e., change tack by jibing rather than coming about. Racing sailboats do this because most modern sailboats (especially larger boats with spinnakers and a variety of staysails) sail substantially faster on a broad reach than running dead before the wind. The extra speed gained by zigzagging downwind can more than make up for the extra distance that must be covered. Cruising boats also often tack downwind when the swells are also coming from dead astern (i.e., there is a "following sea"), because of the more stable motion of the hull.

===Beating===

[[Image:Jibing_Intervals_2.jpg|thumb|right|300px|Depending on the situation, different intervals between tacking can be used. This does not influence the total distance travelled.]]

'''Beating''' is the procedure by which a ship moves on a zig-zag course to make progress directly in to the wind (upwind). No sailing vessel can move directly upwind but that may be the direction it wants to go. Beating allows the vessel to advance directly upwind.

A ship that is beating will sail as close to the wind as possible; this position is known as [[close hauled]]. In general, the closest angle to the wind that a ship can sail is around 35 to 45 degrees. Some modern yachts can sail very near to the wind, while older ships, especially [[square-rigged]] ships, were much worse at it.

Thus when a ship is tacking, it is moving both upwind and across the wind. Cross-wind movement is not desired, and may be very much undesirable, if for instance the ship is moving along a narrow channel, or the destination is directly upwind.

Therefore the ship changes tack periodically, reversing the direction of cross-wind movement while continuing the upwind movement. The interval between tacks depends on the lateral space available: in a small navigable channel, tacks may be required every few minutes, while in the open ocean days may pass between tacks, providing that the wind continues to come from the same general direction.

In older vessels that could not sail close to the wind, beating could be a tiresome process that required sailing a total distance several times the distance actually traveled upwind.