The tonne referred to as the metric ton in the United States and Canada, is a non-SI metric unit of mass equal to 1,000 kilograms or one megagram. It is equivalent to 2,204.6 pounds, 1.102 short tons or 0.984 long tons. Although not part of the SI, the tonne is accepted for use with SI units and prefixes by the International Committee for Weights and Measures; the tonne is derived from the weight of 1 cubic metre of pure water. The SI symbol for the tonne is't', adopted at the same time as the unit in 1879, its use is official for the metric ton in the United States, having been adopted by the United States National Institute of Standards and Technology. It is a symbol, not an abbreviation, should not be followed by a period. Use of upper and lower case is significant, use of other letter combinations is not permitted and would lead to ambiguity. For example,'T','MT','Mt','mt' are the SI symbols for the tesla, megatesla and millitonne respectively. If describing TNT equivalent units of energy, this is equivalent to 4.184 petajoules.
In French and most varieties of English, tonne is the correct spelling. It is pronounced the same as ton, but when it is important to clarify that the metric term is meant, rather than short ton, the final "e" can be pronounced, i.e. "tonny". In Australia, it is pronounced. Before metrication in the UK the unit used for most purposes was the Imperial ton of 2,240 pounds avoirdupois or 20 hundredweight, equivalent to 1,016 kg, differing by just 1.6% from the tonne. The UK Weights and Measures Act 1985 explicitly excluded from use for trade certain imperial units, including the ton, unless the item being sold or the weighing equipment being used was weighed or certified prior to 1 December 1980, then only if the buyer was made aware that the weight of the item was measured in imperial units. In the United States metric ton is the name for this unit used and recommended by NIST. Both spellings are acceptable in Canadian usage. Ton and tonne are both derived from a Germanic word in general use in the North Sea area since the Middle Ages to designate a large cask, or tun.
A full tun, standing about a metre high, could weigh a tonne. An English tun of wine weighs a tonne, 954 kg if full of water, a little less for wine; the spelling tonne pre-dates the introduction of the SI in 1960. In the United States, the unit was referred to using the French words millier or tonneau, but these terms are now obsolete; the Imperial and US customary units comparable to the tonne are both spelled ton in English, though they differ in mass. One tonne is equivalent to: Metric/SI: 1 megagram. Equal to 1000000 grams or 1000 kilograms. Megagram, Mg, is the official SI unit. Mg is distinct from milligram. Pounds: Exactly 1000/0.453 592 37 lb, or 2204.622622 lb. US/Short tons: Exactly 1/0.907 184 74 short tons, or 1.102311311 ST. One short ton is 0.90718474 t. Imperial/Long tons: Exactly 1/1.016 046 9088 long tons, or 0.9842065276 LT. One long ton is 1.0160469088 t. For multiples of the tonne, it is more usual to speak of millions of tonnes. Kilotonne and gigatonne are more used for the energy of nuclear explosions and other events in equivalent mass of TNT loosely as approximate figures.
When used in this context, there is little need to distinguish between metric and other tons, the unit is spelt either as ton or tonne with the relevant prefix attached. *The equivalent units columns use the short scale large-number naming system used in most English-language countries, e.g. 1 billion = 1,000 million = 1,000,000,000.†Values in the equivalent short and long tons columns are rounded to five significant figures, see Conversions for exact values.ǂThough non-standard, the symbol "kt" is used for knot, a unit of speed for aircraft and sea-going vessels, should not be confused with kilotonne. A metric ton unit can mean 10 kilograms within metal trading within the US, it traditionally referred to a metric ton of ore containing 1% of metal. The following excerpt from a mining geology textbook describes its usage in the particular case of tungsten: "Tungsten concentrates are traded in metric tonne units (originally designating one tonne of ore containing 1% of WO3, today used to measure WO3 quantities in 10 kg units.
One metric tonne unit of tungsten contains 7.93 kilograms of tungsten." Note that tungsten is known as wolfram and has the atomic symbol W. In the case of uranium, the acronym MTU is sometimes considered to be metric ton of uranium, meaning 1,000 kg. A gigatonne of carbon dioxide equivalent is a unit used by the UN climate change panel, IPCC, to measure the effect of a technolo
The inch is a unit of length in the imperial and United States customary systems of measurement. It is equal to 1⁄12 of a foot. Derived from the Roman uncia, the word inch is sometimes used to translate similar units in other measurement systems understood as deriving from the width of the human thumb. Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s it has been based on the metric system and defined as 25.4 mm. The English word "inch" was an early borrowing from Latin uncia not present in other Germanic languages; the vowel change from Latin /u/ to Old English /y/ is known as umlaut. The consonant change from the Latin /k/ to English /tʃ/ is palatalisation. Both were features of Old English phonology. "Inch" is cognate with "ounce", whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce. In many other European languages, the word for "inch" is the same as or derived from the word for "thumb", as a man's thumb is about an inch wide.
Examples include Afrikaans: duim. The inch is a used customary unit of length in the United States and the United Kingdom, it is used in Japan for electronic parts display screens. In most of continental Europe, the inch is used informally as a measure for display screens. For the United Kingdom, guidance on public sector use states that, since 1 October 1995, without time limit, the inch is to be used as a primary unit for road signs and related measurements of distance and may continue to be used as a secondary or supplementary indication following a metric measurement for other purposes; the international standard symbol for inch is in but traditionally the inch is denoted by a double prime, approximated by double quotes, the foot by a prime, approximated by an apostrophe. For example, three feet two inches can be written as 3′ 2″. Subdivisions of an inch are written using dyadic fractions with odd number numerators. 1 international inch is equal to: 10,000 tenths 1,000 thou or mil 100 points or gries 72 PostScript points 10, 12, 16, or 40 lines 6 computer picas 3 barleycorns 25.4 millimetres 0.999998 US Survey inches 1/3 or 0.333 palms 1/4 or 0.25 hands 1/12 or 0.08333 feet 1/36 or 0.02777 yards The earliest known reference to the inch in England is from the Laws of Æthelberht dating to the early 7th century, surviving in a single manuscript, the Textus Roffensis from 1120.
Paragraph LXVII sets out the fine for wounds of various depths: one inch, one shilling, two inches, two shillings, etc. An Anglo-Saxon unit of length was the barleycorn. After 1066, 1 inch was equal to 3 barleycorns, which continued to be its legal definition for several centuries, with the barleycorn being the base unit. One of the earliest such definitions is that of 1324, where the legal definition of the inch was set out in a statute of Edward II of England, defining it as "three grains of barley and round, placed end to end, lengthwise". Similar definitions are recorded in both Welsh medieval law tracts. One, dating from the first half of the 10th century, is contained in the Laws of Hywel Dda which superseded those of Dyfnwal, an earlier definition of the inch in Wales. Both definitions, as recorded in Ancient Laws and Institutes of Wales, are that "three lengths of a barleycorn is the inch". King David I of Scotland in his Assize of Weights and Measures is said to have defined the Scottish inch as the width of an average man's thumb at the base of the nail including the requirement to calculate the average of a small, a medium, a large man's measures.
However, the oldest surviving manuscripts date from the early 14th century and appear to have been altered with the inclusion of newer material. In 1814, Charles Butler, a mathematics teacher at Cheam School, recorded the old legal definition of the inch to be "three grains of sound ripe barley being taken out the middle of the ear, well dried, laid end to end in a row", placed the barleycorn, not the inch, as the base unit of the English Long Measure system, from which all other units were derived. John Bouvier recorded in his 1843 law dictionary that the barleycorn was the fundamental measure. Butler observed, that "s the length of the barley-corn cannot be fixed, so the inch according to this method will be uncertain", noting that a standard inch measure was now kept in the Exchequer chamber and, the legal definition of the inch; this was a point made by George Long in his 1842 Penny Cyclopædia, observing that st
The Kriegsmarine was the navy of Nazi Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire and the inter-war Reichsmarine of the Weimar Republic; the Kriegsmarine was one of three official branches, along with the Heer and the Luftwaffe of the Wehrmacht, the German armed forces from 1933 to 1945. In violation of the Treaty of Versailles, the Kriegsmarine grew during German naval rearmament in the 1930s; the 1919 treaty had limited the size of the German navy and prohibited the building of submarines. Kriegsmarine ships were deployed to the waters around Spain during the Spanish Civil War under the guise of enforcing non-intervention, but in reality supported the Nationalist side against the Spanish Republicans. In January 1939 Plan Z was ordered, calling for surface naval parity with the British Royal Navy by 1944; when World War II broke out in September 1939, Plan Z was shelved in favour of a crash building program for submarines instead of capital surface warships and land and air forces were given priority of strategic resources.
The Commander-in-Chief of the Kriegsmarine was the "Führer" Adolf Hitler, who exercised his authority through the Oberkommando der Marine. The Kriegsmarine's most significant ships were the U-boats, most of which were constructed after Plan Z was abandoned at the beginning of World War II. Wolfpacks were assembled groups of submarines which attacked British convoys during the first half of the Battle of the Atlantic but this tactic was abandoned by May 1943 when U-boat losses mounted. Along with the U-boats, surface commerce raiders were used to disrupt Allied shipping in the early years of the war, the most famous of these being the heavy cruisers Admiral Graf Spee and Admiral Scheer and the battleship Bismarck. However, the adoption of convoy escorts in the Atlantic reduced the effectiveness of surface commerce raiders against convoys. After the Second World War in 1945, the Kriegsmarine's remaining ships were divided up among the Allied powers and were used for various purposes including minesweeping.
Under the terms of the 1919 Treaty of Versailles, Germany was only allowed a minimal navy of 15,000 personnel, six capital ships of no more than 10,000 tons, six cruisers, twelve destroyers, twelve torpedo boats and no submarines or aircraft carriers. Military aircraft were banned, so Germany could have no naval aviation. Under the treaty Germany could only build new ships to replace old ones. All the ships allowed and personnel were taken over from the Kaiserliche Marine, renamed Reichsmarine. From the outset, Germany worked to circumvent the military restrictions of the Treaty of Versailles. Through German-owned front companies, the Germans continued to develop U-boats through a submarine design office in the Netherlands and a torpedo research program in Sweden where the G7e torpedo was developed. Before the Nazi seizure of power on 30 January 1933 the German government decided on 15 November 1932 to launch a prohibited naval re-armament program that included U-boats, airplanes and an aircraft carrier.
The launching of the first pocket battleship, Deutschland in 1931 was a step in the formation of a modern German fleet. The building of the Deutschland caused consternation among the French and the British as they had expected that the restrictions of the Treaty of Versailles would limit the replacement of the pre-dreadnought battleships to coastal defence ships, suitable only for defensive warfare. By using innovative construction techniques, the Germans had built a heavy ship suitable for offensive warfare on the high seas while still abiding by the letter of the treaty; when the Nazis came to power in 1933, Adolf Hitler soon began to more brazenly ignore many of the Treaty restrictions and accelerated German naval rearmament. The Anglo-German Naval Agreement of 18 June 1935 allowed Germany to build a navy equivalent to 35% of the British surface ship tonnage and 45% of British submarine tonnage; that same year the Reichsmarine was renamed as the Kriegsmarine. In April 1939, as tensions escalated between the United Kingdom and Germany over Poland, Hitler unilaterally rescinded the restrictions of the Anglo-German Naval Agreement.
The building-up of the German fleet in the time period of 1935–1939 was slowed by problems with marshaling enough manpower and material for ship building. This was because of the simultaneous and rapid build-up of the German army and air force which demanded substantial effort and resources; some projects, like the P-class cruisers, had to be cancelled. The first military action of the Kriegsmarine came during the Spanish Civil War. Following the outbreak of hostilities in July 1936 several large warships of the German fleet were sent to the region; the heavy cruisers Deutschland and Admiral Scheer, the light cruiser Köln were the first to be sent in July 1936. These large ships were accompanied by the 2nd Torpedo-boat Flotilla; the German presence was used to covertly support Franco's Nationalists although the immediate involvement of the Deutschland was humanitarian relief operations and evacuating 9,300 refugees, including 4,550 German citizens. Following the brokering of the International Non-Intervention Patrol to enforce an international arms embargo the Kriegsmarine was allotted the patrol area between Cabo de Gata and Cabo de Oropesa.
Numerous vessels served as part of these duties
Ship commissioning is the act or ceremony of placing a ship in active service, may be regarded as a particular application of the general concepts and practices of project commissioning. The term is most applied to the placing of a warship in active duty with its country's military forces; the ceremonies involved are rooted in centuries old naval tradition. Ship naming and launching endow a ship hull with her identity, but many milestones remain before she is completed and considered ready to be designated a commissioned ship; the engineering plant and electronic systems and multitudinous other equipment required to transform the new hull into an operating and habitable warship are installed and tested. The prospective commanding officer, ship's officers, the petty officers, seamen who will form the crew report for training and intensive familiarization with their new ship. Prior to commissioning, the new ship undergoes sea trials to identify any deficiencies needing correction; the preparation and readiness time between christening-launching and commissioning may be as much as three years for a nuclear powered aircraft carrier to as brief as twenty days for a World War II landing ship.
USS Monitor, of American Civil War fame, was commissioned less than three weeks after launch. Regardless of the type of ship in question, a vessel's journey towards commissioning in its nation's navy begins with a process known as sea trials. Sea trials take place some years after a vessel was laid down, mark the interim step between the completion of a ship's construction and its official acceptance for service with its nation's navy. Sea trials begin when the ship in question is floated out of its dry dock, at which time the initial crew for a ship will assume command of the vessel in question; the ship is sailed in littoral waters for the purpose of testing the design and other ship specific systems to ensure that they work properly and can handle the equipment that they will be using in the coming years. Tests done during this phase can include launching missiles from missile magazines, firing the ship's gun, conducting basic flight tests with rotary and fixed-wing aircraft that will be assigned to the ship in the future, various tests of the electronic and propulsion equipment.
During this phase of testing problems arise relating to the state of the equipment on the ship in question, which can result in the ship returning to the builder's shipyard to address the concerns in question. In addition to problems with a ship's arms and equipment, the sea trial phase a ship undergoes prior to commissioning can identify issues with the ship's design that may need to be addressed before it can be accepted into service with its nation's navy. During her sea trials in 1999 French Naval officials determined that the French aircraft carrier Charles de Gaulle was too short to safely operate the E2C Hawkeye, resulting in her return to the builder's shipyard for enlargement. After a ship has cleared its sea trial period, it will be accepted into service with its nation's navy. At this point, the ship in question will undergo a process of degaussing and/or deperming, which will vastly reduce the ship in question's magnetic signature. Once a ship's sea trials are completed plans for the actual commissioning ceremony will take shape.
Depending on the naval traditions of the nation in question, the commissioning ceremony may be an elaborately planned event with guests, the ship's future crew, other persons of interest in attendance, or the nation in question may forgo a ceremony and instead administratively place the ship in commission. At a minimum, on the day on which the ship in question is to be commissioned the crew will report for duty aboard the ship and the commanding officer will read through the orders given for the ship and its personnel. If the ship's ceremony is a public affair the Captain may make a speech to the audience, along with other VIPs as the ceremony dictates. Religious ceremonies, such as blessing the ship or the singing of traditional hymns or songs, may occur. Once a ship has been commissioned its final step toward becoming an active unit of the navy it now serves is to report to its home port and load or accept any remaining equipment. To decommission a ship is to terminate its career in service in the armed forces of a nation.
Unlike wartime ship losses, in which a vessel lost to enemy action is said to be struck, decommissioning confers that the ship has reached the end of its usable life and is being retired from a given country's navy. Depending on the naval traditions of the country in question, a ceremony commemorating the decommissioning of the ship in question may take place, or the vessel may be removed administratively with little to no fanfare; the term "paid off" is alternatively used in British Commonwealth contexts, originating in the age-of-sail practice of ending an officer's commission and paying crew wages once the ship completed its voyage. Ship decommissioning occurs some years after the ship was commissioned and is intended to serve as a means by which a vessel that has become too old or too obsolete can be retired with honor from the operating country's armed force. Decommissioning of the vessel may occur due to treaty agreements or for safety reasons (such as a ship's nuclear reactor and assoc
Siemens-Schuckert was a German electrical engineering company headquartered in Berlin and Nuremberg, incorporated into the Siemens AG in 1966. Siemens Schuckert was founded in 1903 when Halske acquired Schuckertwerke. Subsequently, Siemens & Halske specialized in communications engineering and Siemens-Schuckert in power engineering and pneumatic instrumentation. During World War I Siemens-Schuckert produced aircraft, it took over manufacturing of the renowned Protos vehicles in 1908. In World War II, the company had a factory producing aircraft and other parts at Monowitz near Auschwitz. There was a workers camp near the factory known as Bobrek concentration camp; the Siemens Schuckert logo consisted of an S with a smaller S superimposed on the middle with the smaller S rotated left by 45 degrees. The logo was used into the late 1960s, when both companies merged with the Siemens-Reiniger-Werke AG to form the present-day Siemens AG. Siemens-Schuckert built a number of designs in inter-war era, they produced aircraft engines under the Siemens-Halske brand, which evolved into their major product line after the end of World War I.
The company reorganized as Brandenburgische Motorenwerke, or Bramo, in 1936, were purchased in 1939 by BMW to become BMW Flugmotorenbau. Siemens-Schuckert designed a number of heavy bombers early in World War I, building a run of seven Riesenflugzeug. Intended to be used in the strategic role in long duration flights, the SSW R-series had three 150 h.p Benz Bz. III engines in the cabin driving two propellers connected to a common gear-box through a combination leather-cone and centrifugal-key clutch in SSW R. I to the SSW R. VII models. In the case of engine failure, common at the time, the bomber could continue flying on two engines while the third was repaired by the in-flight mechanic. Two transmission shafts transferred the power from the gear-box to propeller gear-boxes mounted on the wing struts. Although there were some problems with the clutch system, the gear-box proved to be reliable when properly maintained; the SSW R.1 through the SSW R. VII designs were noted for their distinctive forked fuselage.
Several of these aircraft fought on the Eastern Front. Although interesting in concept, the cost of these and the R-types from other companies was so great that the air force abandoned the concept until more practical designs arrived in the war; the first fighter designed at the works was the Siemens-Schuckert E. I which appeared in mid 1915, was the first aircraft to be powered by the Siemens-Halske Sh. I, a new rotary, developed by Siemens-Schuckert, in which the cylinders and the propeller rotated in opposite directions. A small number of production machines were supplied to various Feldflieger Abteilung to supplement supplies of the Fokker and Pfalz monoplane fighters used at the time for escort work; the prototype SSW E. II, powered by the inline Argus AsII, crashed in June 1916, killing Franz Steffen, one of the designers of the SSW R types. By early 1916 the first generation of German monoplane fighters were outclassed by the Nieuport 11 and the Nieuport 17 which quickly followed it; the resulting SSW D.
I was powered by the Siemens-Halske Sh. I, but was otherwise a literal copy of the Nieuport 17; this aircraft was the first Siemens-Schuckert fighter to be ordered in quantity, but by the time it became available in numbers it was outclassed by contemporary Albatros fighters. Development of the Sh. I 160 hp Sh. III one of the most advanced rotary engine designs of the war; the D. I fighter formed the basis for a series of original designs, which by the end of 1917 had reached a peak in the Siemens-Schuckert D. III, which went into limited production in early 1918, found use in home defense units as an interceptor, due to its outstanding rate of climb. Further modifications improved its handling and performance to produce the Siemens-Schuckert D. IV. Several offshoots of the design included triplanes and a parasol monoplane. With the end of the war production of the D. IV continued for sales to Switzerland who flew them into the late 1920s. With the signing of the Treaty of Versailles the next year all aircraft production in Germany was shut down.
Siemens-Schuckert disappeared, but Siemens-Halske continued sales of the Sh. III and started development of smaller engines for the civilian market. By the mid-1920s their rotary engines were no longer in vogue, but "non-turning" versions of the same basic mechanicals led to a series of 7-cylinder radial engines, the Sh.10 through Sh.14A, delivering up to 150 hp in the 14A. The Sh.14A became a best-seller in the trainer market, over 15,000 of all the versions were built. Siemens-Halske no longer had any competitive engines for the larger end of the market, to address this they negotiated a license in 1929 to produce the 9-cylinder Bristol Jupiter IV. Minor changes for the German market led to the Sh.20 and Sh.21. Following the evolution of their smaller Sh.14's, the engine was bored out to produce the 900 hp design, the Sh.22. In 1933 new engine naming was introduced by the RLM, this design became the Sh.322, when Siemens was given the 300-block of numbers. The Sh.322 design never became popular.
The company reorganized as Bramo in 1936, continued development of what was now their own large engine. Modifying the Sh.322 with the addition of fuel injection and a new supercharger led to the Bramo 323 Fafnir, which entered production in 1937. Although ra
A submarine hull has two major components, the light hull and the pressure hull. The light hull of a submarine is the outer non-watertight hull which provides a hydrodynamically efficient shape; the pressure hull is the inner hull of a submarine that maintains structural integrity with the difference between outside and inside pressure at depth. Modern submarines are cigar-shaped; this design visible on early submarines is called a "teardrop hull", was patterned after the bodies of whales. It reduces the hydrodynamic drag on the sub when submerged, but decreases the sea-keeping capabilities and increases the drag while surfaced; the concept of an outer hydrodynamically streamlined light hull separated from the inner pressure hull was first introduced in the early pioneering submarine Ictineo I designed by the Catalan inventor Narcís Monturiol in 1859. However, when military submarines entered service in the early 1900s, the limitations of their propulsion systems forced them to operate on the surface most of the time.
Because of the slow submerged speeds of these submarines well below 10 knots, the increased drag for underwater travel by the conventional ship like outer hull was considered acceptable. Only late in World War II, when technology enhancements allowed faster and longer submerged operations and increased surveillance by enemy aircraft forced submarines to spend most of their times below the surface, did hull designs become teardrop shaped again, to reduce drag and noise. USS Albacore was a unique research submarine that pioneered the American version of the teardrop hull form of modern submarines. On modern military submarines the outer hull is covered with a thick layer of special sound-absorbing rubber, or anechoic plating, to make the submarine more difficult to detect by active and passive SONAR. All small modern submarines and submersibles, as well as the oldest ones, have a single hull. However, for large submarines, the approaches have separated. All Soviet heavy submarines are built with a double hull structure, but American submarines are single-hulled.
They still have light hull sections in bow and stern, which house main ballast tanks and provide hydrodynamically optimized shape, but the main cylindrical, hull section has only a single plating layer. The double hull of a submarine is different from a ship's double hull; the external hull, which forms the shape of submarine, is called the outer hull, casing or light hull. This term is appropriate for Russian submarine construction, where the light hull is made of thin steel plate, as it has the same pressure on both sides; the light hull can be used to mount equipment, which if attached directly to the pressure hull could cause unnecessary stress. The double hull approach saves space inside the pressure hull, as the ring stiffeners and longitudinals can be located between the hulls; these measures help minimise the size of the pressure hull, much heavier than the light hull. In case the submarine is damaged, the light hull takes some of the damage and does not compromise the vessel's integrity, as long as the pressure hull is intact.
Inside the outer hull there is a strong hull, or pressure hull, which withstands the outside pressure and has normal atmospheric pressure inside. The pressure hull is constructed of thick high-strength steel with a complex structure and high strength reserve, is separated with watertight bulkheads into several compartments; the pressure and light hulls aren't separated, form a three-dimensional structure with increased strength. The interhull space is used for some of the equipment which doesn't require constant pressure to operate; the list differs between submarines, includes different water/air tanks. In case of a single-hull submarine, the light hull and the pressure hull are the same except for the bow and stern; the constructions of a pressure hull requires a high degree of precision. This is true irrespective of its size. A one inch deviation from cross-sectional roundness results in over 30 percent decrease of hydrostatic load. Minor deviations are resisted by the stiffener rings, the total pressure force of several million longitudinally-oriented tons must be distributed evenly over the hull by using a hull with circular cross section.
This design is the most resistant to compressive stress and without it no material could resist water pressure at submarine depths. A submarine hull requires expensive transversal construction, with stiffener rings located more than the longitudinals. No hull parts may contain defects, all welded joints are checked several times with different methods. Typhoon-class submarines feature multiple pressure hulls that simplify internal design while making the vessel much wider than a normal submarine. In the main body of the sub, two long pressure hulls lie parallel with a third, smaller pressure hull above them, two other pressure hulls for torpedoes and steering gear; this greatly increases their survivability - if one pressure hull is breached, the crew members in the other are safe and there is less potential for flooding. The dive depth cannot be increased easily. Making the hull thicker increases the weight and requires reduction of the weight of onboard equipment resulting in a bathyscaphe.
This is affordable for civilian research submersibles, but not military su
A sloop is a sailing boat with a single mast and a fore-and-aft rig. A sloop has only one head-sail; the most common rig of modern sailboats is the Bermuda-rigged sloop. A modern sloop carries a mainsail on a boom aft of the mast, with a single loose-footed head-sail forward of the mast. Sloops are either fractional-rigged. On a masthead-rigged sloop, the forestay attaches at the top of the mast. On a fractional-rigged sloop, the forestay attaches to the mast at a point below the top 3/4 of the way to top, or 7/8 or some other fraction. Compared to a masthead-rigged sloop, the mast of a fractional-rigged sloop may be placed farther forward. After the cat rig which has only a single sail, the sloop rig is one of the simpler sailing rig configurations. A sloop has two sails, a mainsail and a headsail, while the cutter has a mainsail and two or more headsails. Next in complexity are the ketch, the yawl and the schooner, each of which has two masts and a minimum of three sails. A sloop has a simple system of mast rigging -- a backstay and shrouds.
By having only two sails, the individual sails of a sloop are larger than those of an equivalent cutter, yawl or ketch. Until the advent of lightweight sailcloth and modern sail-handling systems, the larger sails of a sloop could be a handful. So, until the 1950s, sailboats over 10 metres length overall would use a cutter rig or a two-mast rig. After the advent of modern winches and light sailcloth, the sloop became the dominant sailing rig type for all but the largest sailboats. No rig type is perfect for all conditions. Sloops, with their paucity of spars and control lines, tend to impart less aerodynamic drag. Compared to other rigs, sloops tend to perform well when sailing close hauled to windward and offer a sound overall compromise of abilities on all points of sail. Cutters and yawls are preferred to sloops when venturing far offshore, because it is easier to reef small sails as the wind increases, while still keeping the boat balanced. To maximize the amount of sail carried, the classic sloop may use a bowsprit, a spar that projects forward from the bow.
The foresail may be a jib, which does not overlap the mast more than 10 to 20 percent, or a much larger genoa. The genoa's large overlap behind the mainsail helps to guide the airflow and thereby makes the mainsail more effective. For downwind sailing, the jib or genoa may be replaced by larger curved sails known as spinnakers or gennakers. Nowadays, by far the most common sloop rig, for yachts and dinghies, is the Bermuda rig, the optimal rig for upwind sailing. Originating from the island of Bermuda in the 17th century, the Bermuda rig is simple, yet may be tuned to be maneuverable and fast; the main disadvantage is the large size of the sails on larger vessels. It is less successful sailing downwind, when the addition of a spinnaker becomes necessary for faster progress in all but the strongest winds. However, the spinnaker is an intrinsically unstable sail requiring continuous trimming. An alternative downwind sailplan, more stable but slower, is the "wing on wing". Here, the main is swung wide to lee while the jib is swung wide to windward.
However the "wing on wing" configuration tends to dip the bow, requiring crew to move aft to counterbalance the dip. The wing on wing configuration cannot be heeled over to decrease waterline whereas the spinnaker configuration can be. If not tended the main can go slack to the point of being dangerously close to jibing; the jib will have that same tendency and being to windward, will snap a-lee but with no boom and being forward of the mast will make for a far less dangerous move than that of the main. A slack main when to leeward can be brought back under control by hauling on the mainsheet to bring it back in contact with the wind when on the aft quarter to windward but if the wind comes around onto the aft quarter of what had been to lee, the boat must be brought further a-lee to keep the wind strong on the main. Jamaican sloops had beams that were narrower than ocean-going Bermuda sloops, could attain a speed of around 12 knots, they carried gaff rig. The keel of Jamaican sloops would be between 50–75 feet, but could be built longer.
Jamaican sloops were built near the shore and out of cedar trees, for much the same reasons that Bermudian shipwrights favoured the Bermuda cedar: these were resistant to rot, grew fast and tall, had a taste displeasing to marine borers. Cedar was favoured over oak as the latter would rot in about 10 years, while cedar would last for nigh on 30 years and was lighter than oak. Since piracy was a significant threat in Caribbean waters, merchants sought ships that could outrun pursuers; that same speed and maneuverability made them prized and more targeted by the pirates they were designed to avoid. When the ships needed to be de-fouled from seaweed and barnacles, pirates needed a safe haven on which to car