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85-475: Lindaliini AS was founded in 1997 as the successor of shipping company Inreko Laeva AS. It started operations with a fleet of three hydrofoils , which were able to make the journey between Tallinn and Helsinki in an hour and a half, much faster than the conventional ferries serving the same route. Starting in 2007, the hydrofoils were replaced with catamarans , which were less expensive to maintain and had better seaworthiness. Still catamarans are more dependent on

170-413: A 400 watt motor, it can reach speeds exceeding 14 km/h with a weight of 22 kg. A single charge of the battery lasts an hour for a rider weighing 85 kg. Candela, a Swedish company, is producing a recreational hydrofoil powerboat, making strong claims for efficiency, performance, and range. Hydrofoils are now widely used with kitesurfing , that is traction kites over water. Hydrofoils are

255-627: A Parisian. He claimed that "adapting to the sides and bottom of the vessel a series or inclined planes or wedge formed pieces, which as the vessel is driven forward will have the effect of lifting it in the water and reducing the draught.". Italian inventor Enrico Forlanini began work on hydrofoils in 1898 and used a "ladder" foil system. Forlanini obtained patents in Britain and the United States for his ideas and designs. Between 1899 and 1901, British boat designer John Thornycroft worked on

340-633: A certain displacement, so most hydrofoil craft are relatively small, and are mainly used as high-speed passenger ferries, where the relatively high passenger fees can offset the high cost of the craft itself. However, the design is simple enough that there are many human-powered hydrofoil designs. Amateur experimentation and development of the concept is popular. Since air and water are governed by similar fluid equations —albeit with different levels of viscosity , density , and compressibility —the hydrofoil and airfoil (both types of foil ) create lift in identical ways. The foil shape moves smoothly through

425-435: A distance s 2 = v 2 Δ t . The displaced fluid volumes at the inflow and outflow are respectively A 1 s 1 and A 2 s 2 . The associated displaced fluid masses are – when ρ is the fluid's mass density – equal to density times volume, so ρA 1 s 1 and ρA 2 s 2 . By mass conservation, these two masses displaced in the time interval Δ t have to be equal, and this displaced mass

510-863: A distinct type, but also employing lift) a very significant achievement, and after reading the article began to sketch concepts of what is now called a hydrofoil boat. With his chief engineer Casey Baldwin , Bell began hydrofoil experiments in the summer of 1908. Baldwin studied the work of the Italian inventor Enrico Forlanini and began testing models based on those designs, which led to the development of hydrofoil watercraft. During Bell's world tour of 1910–1911, Bell and Baldwin met with Forlanini in Italy, where they rode in his hydrofoil boat over Lake Maggiore . Baldwin described it as being as smooth as flying. On returning to Bell's large laboratory at his Beinn Bhreagh estate near Baddeck, Nova Scotia , they experimented with

595-427: A fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where

680-407: A hydrofoil craft gains speed, the hydrofoils lift the boat's hull out of the water, decreasing drag and allowing greater speeds. The hydrofoil was created by Eric Walters. The hydrofoil usually consists of a winglike structure mounted on struts below the hull , or across the keels of a catamaran in a variety of boats (see illustration). As a hydrofoil-equipped watercraft increases in speed,

765-550: A new trend in windsurfing - including the new Summer Olympic class, the IQFoil , and more recently with Wing foiling , which are essentially a kite with no strings, or a hand-held sail. Soviet-built Voskhods are one of the most successful passenger hydrofoil designs. Manufactured in Soviet and later Ukrainian Crimea, they are in service in more than 20 countries. The most recent model, Voskhod-2M FFF , also known as Eurofoil,

850-677: A number of designs, culminating in Bell's HD-4 . Using Renault engines, a top speed of 87 km/h (47 kn; 54 mph) was achieved, accelerating rapidly, taking waves without difficulty, steering well and showing good stability. Bell's report to the United States Navy permitted him to obtain two 260 kW (350 hp) engines. On 9 September 1919 the HD-4 set a world marine speed record of 114 km/h (62 kn; 71 mph), which stood for two decades. A full-scale replica of

935-575: A particular application, but all are analogous to Bernoulli's equation and all rely on nothing more than the fundamental principles of physics such as Newton's laws of motion or the first law of thermodynamics . For a compressible fluid, with a barotropic equation of state , and under the action of conservative forces, v 2 2 + ∫ p 1 p d p ~ ρ ( p ~ ) + Ψ = constant (along

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1020-468: A series of models with a stepped hull and single bow foil. In 1909 his company built the full scale 22-foot (6.7 m) long boat, Miranda III . Driven by a 60 hp (45 kW) engine, it rode on a bowfoil and flat stern. The subsequent Miranda IV was credited with a speed of 35 kn (65 km/h; 40 mph). In May 1904 a hydrofoil boat was described being tested on the River Seine "in

1105-534: A speed of 50.17 knots (92.91 km/h). The 500 m speed record for sailboats is currently held by the Vestas Sailrocket , an exotic design which operates in effect as a hydrofoil. Another trimaran sailboat is the Windrider Rave. The Rave is a commercially available 17-foot (5.2 m), two person, hydrofoil trimaran, capable of reaching speeds of 40 kn (74 km/h). The boat

1190-561: A standard E-boat over the next three years it performed well but was not brought into production. Being faster it could carry a higher payload and was capable of travelling over minefields but was prone to damage and noisier. In Canada during World War II, Baldwin worked on an experimental smoke laying hydrofoil (later called the Comox Torpedo) that was later superseded by other smoke-laying technology and an experimental target-towing hydrofoil. The forward two foil assemblies of what

1275-461: A streamline) {\displaystyle {\frac {v^{2}}{2}}+\int _{p_{1}}^{p}{\frac {\mathrm {d} {\tilde {p}}}{\rho \left({\tilde {p}}\right)}}+\Psi ={\text{constant (along a streamline)}}} where: In engineering situations, elevations are generally small compared to the size of the Earth, and the time scales of fluid flow are small enough to consider the equation of state as adiabatic. In this case,

1360-487: A trimaran-type vessel for the Tallinn–Helsinki route, intended to replace hydrofoil Jaanika. The trimaran would have been safer and slightly larger than Merilin. The launch was initially planned for April 2009, but this was soon postponed to June 26, and the purchase was ultimately not completed for unknown reasons. Linda Line started the 2009 season with two catamarans, Merilin and the newly acquired Karolin. In Tallinn,

1445-483: Is a Bernoulli equation valid also for unsteady—or time dependent—flows. Here ⁠ ∂ φ / ∂ t ⁠ denotes the partial derivative of the velocity potential φ with respect to time t , and v = | ∇ φ | is the flow speed. The function f ( t ) depends only on time and not on position in the fluid. As a result, the Bernoulli equation at some moment t applies in the whole fluid domain. This

1530-462: Is a constant, sometimes referred to as the Bernoulli constant. It is not a universal constant , but rather a constant of a particular fluid system. The deduction is: where the speed is large, pressure is low and vice versa. In the above derivation, no external work–energy principle is invoked. Rather, Bernoulli's principle was derived by a simple manipulation of Newton's second law. Another way to derive Bernoulli's principle for an incompressible flow

1615-495: Is a flow speed at which pressure is zero, and at even higher speeds the pressure is negative. Most often, gases and liquids are not capable of negative absolute pressure, or even zero pressure, so clearly Bernoulli's equation ceases to be valid before zero pressure is reached. In liquids—when the pressure becomes too low— cavitation occurs. The above equations use a linear relationship between flow speed squared and pressure. At higher flow speeds in gases, or for sound waves in liquid,

1700-512: Is a key concept in fluid dynamics that relates pressure, density, speed and height. Bernoulli's principle states that an increase in the speed of a parcel of fluid occurs simultaneously with a decrease in either the pressure or the height above a datum. The principle is named after the Swiss mathematician and physicist Daniel Bernoulli , who published it in his book Hydrodynamica in 1738. Although Bernoulli deduced that pressure decreases when

1785-558: Is a two-seater, four-foiled hydrofoil electrical leisure watercraft. Its initial design was set in 2012 and it has been available commercially since the end of 2016. Powered by a 5.2-kWh lithium-ion battery pack and propelled by a 5.5 kW motor, it reaches the top speed of 40 km/h and has 80 km of range. The Manta5 Hydrofoiler XE-1 is a Hydrofoil E-bike, designed and built in New Zealand that has since been available commercially for pre-order since late 2017. Propelled by

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1870-885: Is also true for the special case of a steady irrotational flow, in which case f and ⁠ ∂ φ / ∂ t ⁠ are constants so equation ( A ) can be applied in every point of the fluid domain. Further f ( t ) can be made equal to zero by incorporating it into the velocity potential using the transformation: Φ = φ − ∫ t 0 t f ( τ ) d τ , {\displaystyle \Phi =\varphi -\int _{t_{0}}^{t}f(\tau )\,\mathrm {d} \tau ,} resulting in: ∂ Φ ∂ t + 1 2 v 2 + p ρ + g z = 0. {\displaystyle {\frac {\partial \Phi }{\partial t}}+{\tfrac {1}{2}}v^{2}+{\frac {p}{\rho }}+gz=0.} Note that

1955-655: Is believed to be the latter hydrofoil were salvaged in the mid-1960s from a derelict hulk in Baddeck, Nova Scotia by Colin MacGregor Stevens. These were donated to the Maritime Museum in Halifax, Nova Scotia. The Canadian Armed Forces built and tested a number of hydrofoils (e.g., Baddeck and two vessels named Bras d'Or ), which culminated in the high-speed anti-submarine hydrofoil HMCS Bras d'Or in

2040-450: Is by applying conservation of energy. In the form of the work-energy theorem , stating that Therefore, The system consists of the volume of fluid, initially between the cross-sections A 1 and A 2 . In the time interval Δ t fluid elements initially at the inflow cross-section A 1 move over a distance s 1 = v 1 Δ t , while at the outflow cross-section the fluid moves away from cross-section A 2 over

2125-401: Is constant along any given streamline. More generally, when b may vary along streamlines, it still proves a useful parameter, related to the "head" of the fluid (see below). When the change in Ψ can be ignored, a very useful form of this equation is: v 2 2 + w = w 0 {\displaystyle {\frac {v^{2}}{2}}+w=w_{0}} where w 0

2210-409: Is defined to be the total pressure p 0 . The significance of Bernoulli's principle can now be summarized as "total pressure is constant in any region free of viscous forces". If the fluid flow is brought to rest at some point, this point is called a stagnation point, and at this point the static pressure is equal to the stagnation pressure . If the fluid flow is irrotational , the total pressure

2295-562: Is denoted by  Δ m : ρ A 1 s 1 = ρ A 1 v 1 Δ t = Δ m , ρ A 2 s 2 = ρ A 2 v 2 Δ t = Δ m . {\displaystyle {\begin{aligned}\rho A_{1}s_{1}&=\rho A_{1}v_{1}\Delta t=\Delta m,\\\rho A_{2}s_{2}&=\rho A_{2}v_{2}\Delta t=\Delta m.\end{aligned}}} The work done by

2380-429: Is done on or by the gas (so the simple energy balance is not upset). According to the gas law, an isobaric or isochoric process is ordinarily the only way to ensure constant density in a gas. Also the gas density will be proportional to the ratio of pressure and absolute temperature ; however, this ratio will vary upon compression or expansion, no matter what non-zero quantity of heat is added or removed. The only exception

2465-409: Is if the net heat transfer is zero, as in a complete thermodynamic cycle or in an individual isentropic (frictionless adiabatic ) process, and even then this reversible process must be reversed, to restore the gas to the original pressure and specific volume, and thus density. Only then is the original, unmodified Bernoulli equation applicable. In this case the equation can be used if the flow speed of

2550-448: Is sometimes valid for the flow of gases: provided that there is no transfer of kinetic or potential energy from the gas flow to the compression or expansion of the gas. If both the gas pressure and volume change simultaneously, then work will be done on or by the gas. In this case, Bernoulli's equation—in its incompressible flow form—cannot be assumed to be valid. However, if the gas process is entirely isobaric , or isochoric , then no work

2635-404: Is the thermodynamic energy per unit mass, also known as the specific internal energy . So, for constant internal energy e {\displaystyle e} the equation reduces to the incompressible-flow form. The constant on the right-hand side is often called the Bernoulli constant and denoted b . For steady inviscid adiabatic flow with no additional sources or sinks of energy, b

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2720-596: Is the force potential at the point considered. For example, for the Earth's gravity Ψ = gz . By multiplying with the fluid density ρ , equation ( A ) can be rewritten as: 1 2 ρ v 2 + ρ g z + p = constant {\displaystyle {\tfrac {1}{2}}\rho v^{2}+\rho gz+p={\text{constant}}} or: q + ρ g h = p 0 + ρ g z = constant {\displaystyle q+\rho gh=p_{0}+\rho gz={\text{constant}}} where The constant in

2805-436: Is the same everywhere. Bernoulli's principle can also be derived directly from Isaac Newton 's second Law of Motion . If a small volume of fluid is flowing horizontally from a region of high pressure to a region of low pressure, then there is more pressure behind than in front. This gives a net force on the volume, accelerating it along the streamline. Fluid particles are subject only to pressure and their own weight. If

2890-404: Is total enthalpy. For a calorically perfect gas such as an ideal gas, the enthalpy is directly proportional to the temperature, and this leads to the concept of the total (or stagnation) temperature. When shock waves are present, in a reference frame in which the shock is stationary and the flow is steady, many of the parameters in the Bernoulli equation suffer abrupt changes in passing through

2975-497: Is uniform and Bernoulli's principle can be summarized as "total pressure is constant everywhere in the fluid flow". It is reasonable to assume that irrotational flow exists in any situation where a large body of fluid is flowing past a solid body. Examples are aircraft in flight and ships moving in open bodies of water. However, Bernoulli's principle importantly does not apply in the boundary layer such as in flow through long pipes . The Bernoulli equation for unsteady potential flow

3060-669: Is used in the theory of ocean surface waves and acoustics . For an irrotational flow, the flow velocity can be described as the gradient ∇ φ of a velocity potential φ . In that case, and for a constant density ρ , the momentum equations of the Euler equations can be integrated to: ∂ φ ∂ t + 1 2 v 2 + p ρ + g z = f ( t ) , {\displaystyle {\frac {\partial \varphi }{\partial t}}+{\tfrac {1}{2}}v^{2}+{\frac {p}{\rho }}+gz=f(t),} which

3145-559: Is valid for incompressible flows (e.g. most liquid flows and gases moving at low Mach number ). More advanced forms may be applied to compressible flows at higher Mach numbers. In most flows of liquids, and of gases at low Mach number , the density of a fluid parcel can be considered to be constant, regardless of pressure variations in the flow. Therefore, the fluid can be considered to be incompressible, and these flows are called incompressible flows . Bernoulli performed his experiments on liquids, so his equation in its original form

3230-446: Is valid only for incompressible flow. A common form of Bernoulli's equation is: where: Bernoulli's equation and the Bernoulli constant are applicable throughout any region of flow where the energy per unit mass is uniform. Because the energy per unit mass of liquid in a well-mixed reservoir is uniform throughout, Bernoulli's equation can be used to analyze the fluid flow everywhere in that reservoir (including pipes or flow fields that

3315-656: The Sparviero class starting in the late 1970s. These were armed with a 76 mm gun and two missiles, and were capable of speeds up to 50 knots (93 km/h). Three similar boats were built for the Japan Maritime Self-Defense Force . Several editions of the America's Cup have been raced with foiling yachts. In 2013 and 2017 respectively the AC72 and AC50 classes of catamaran , and in 2021

3400-529: The AC75 class of foiling monohulls with canting arms. The French experimental sail powered hydrofoil Hydroptère is the result of a research project that involves advanced engineering skills and technologies. In September 2009, the Hydroptère set new sailcraft world speed records in the 500 m category, with a speed of 51.36 knots (95.12 km/h) and in the 1 nautical mile (1852 m) category with

3485-583: The HD-4 is viewable at the Alexander Graham Bell National Historic Site museum in Baddeck, Nova Scotia. In the early 1950s an English couple built the White Hawk , a jet-powered hydrofoil water craft, in an attempt to beat the absolute water speed record. However, in tests, White Hawk could barely top the record breaking speed of the 1919 HD-4 . The designers had faced an engineering phenomenon that limits

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3570-828: The parcel of fluid is − A d p . If the pressure decreases along the length of the pipe, d p is negative but the force resulting in flow is positive along the x axis. m d v d t = F ρ A d x d v d t = − A d p ρ d v d t = − d p d x {\displaystyle {\begin{aligned}m{\frac {\mathrm {d} v}{\mathrm {d} t}}&=F\\\rho A\mathrm {d} x{\frac {\mathrm {d} v}{\mathrm {d} t}}&=-A\mathrm {d} p\\\rho {\frac {\mathrm {d} v}{\mathrm {d} t}}&=-{\frac {\mathrm {d} p}{\mathrm {d} x}}\end{aligned}}} In steady flow

3655-683: The surface effect principle to create the Ekranoplan . Extensive investment in this type of technology in the USSR resulted in the largest civil hydrofoil fleet in the world and the making of the Meteor type, the most successful hydrofoil in history, with more than 400 units built. In 1961, SRI International issued a study on "The Economic Feasibility of Passenger Hydrofoil Craft in US Domestic and Foreign Commerce". Commercial use of hydrofoils in

3740-410: The Bernoulli equation can be normalized. A common approach is in terms of total head or energy head H : H = z + p ρ g + v 2 2 g = h + v 2 2 g , {\displaystyle H=z+{\frac {p}{\rho g}}+{\frac {v^{2}}{2g}}=h+{\frac {v^{2}}{2g}},} The above equations suggest there

3825-666: The Linda Line high-speed ferries departed from Linnahall terminal and in Helsinki from Makasiini terminal. Both ships had a Linda class and a VIP class separated from the rest of the cabin, and the company offered a variety of hotel and leisure packages in Helsinki. On April 16, 2008, the Tallinn City Government decided to award the contract for the Tallinn-Aegna shipping line to Linda Line. The decision

3910-951: The Ob and the Volga. The Meteor 120R  [ ru ] , a development of the Meteor  [ ru ] , became the Valday's larger sibling, the first ship launched in Nizhny Novgorod in August 2021. The Boeing 929 is widely used in Asia for passenger services, between Hong Kong and Macau and between the many islands of Japan , also on the Korean peninsula . The main user is Hong Kong private corp. Current operators of hydrofoils include: Bernoulli%27s principle Bernoulli's principle

3995-567: The PT150 combining a surface-piercing foil forward with a fully submerged foil in the aft location. Over 200 of Supramar's design were built, most of them by Rodriquez (headed at the time by Engineer Carlo Rodriquez in Sicily , Italy. During the same period the Soviet Union experimented extensively with hydrofoils, constructing hydrofoil river boats and ferries with streamlined designs during

4080-711: The Supramar company. In 1952, Supramar launched the first commercial hydrofoil, PT10 "Freccia d'Oro" (Golden Arrow), in Lake Maggiore, between Switzerland and Italy . The PT10 is of surface-piercing type, it can carry 32 passengers and travel at 35 knots (65 km/h; 40 mph). In 1968, the Bahraini born banker Hussain Najadi acquired the Supramar AG and expanded its operations into Japan, Hong Kong, Singapore,

4165-680: The UK, Norway and the US. General Dynamics of the United States became its licensee, and the Pentagon awarded its first R&D naval research project in the field of supercavitation . Hitachi Shipbuilding of Osaka, Japan, was another licensee of Supramar, as well as many leading ship owners and shipyards in the OECD countries. From 1952 to 1971, Supramar designed many models of hydrofoils: PT20, PT50, PT75, PT100 and PT150. All are of surface-piercing type, except

4250-490: The US first appeared in 1961 when two commuter vessels were commissioned by Harry Gale Nye, Jr. 's North American Hydrofoils to service the route from Atlantic Highlands, New Jersey to the financial district of Lower Manhattan. A 17-ton German craft VS-6 Hydrofoil was designed and constructed in 1940, completed in 1941 for use as a mine layer; it was tested in the Baltic Sea , producing speeds of 47 knots. Tested against

4335-418: The above equation for an ideal gas becomes: v 2 2 + g z + ( γ γ − 1 ) p ρ = constant (along a streamline) {\displaystyle {\frac {v^{2}}{2}}+gz+\left({\frac {\gamma }{\gamma -1}}\right){\frac {p}{\rho }}={\text{constant (along a streamline)}}} where, in addition to

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4420-647: The above equation for isentropic flow becomes: ∂ ϕ ∂ t + ∇ ϕ ⋅ ∇ ϕ 2 + Ψ + γ γ − 1 p ρ = constant {\displaystyle {\frac {\partial \phi }{\partial t}}+{\frac {\nabla \phi \cdot \nabla \phi }{2}}+\Psi +{\frac {\gamma }{\gamma -1}}{\frac {p}{\rho }}={\text{constant}}} The Bernoulli equation for incompressible fluids can be derived by either integrating Newton's second law of motion or by applying

4505-499: The actual pressure of the fluid, which is associated not with its motion but with its state, is often referred to as the static pressure, but where the term pressure alone is used it refers to this static pressure." The simplified form of Bernoulli's equation can be summarized in the following memorable word equation: Every point in a steadily flowing fluid, regardless of the fluid speed at that point, has its own unique static pressure p and dynamic pressure q . Their sum p + q

4590-410: The changes in mass density become significant so that the assumption of constant density is invalid. In many applications of Bernoulli's equation, the change in the ρgz term is so small compared with the other terms that it can be ignored. For example, in the case of aircraft in flight, the change in height z is so small the ρgz term can be omitted. This allows the above equation to be presented in

4675-473: The cold war period and into the 1980s. Such vessels include the Raketa (1957) type, followed by the larger Meteor type and the smaller Voskhod type. One of the most successful Soviet designer/inventor in this area was Rostislav Alexeyev , who some consider the 'father' of the modern hydrofoil due to his 1950s era high speed hydrofoil designs. Later, circa 1970s, Alexeyev combined his hydrofoil experience with

4760-455: The effects of wave action, and, therefore, more stable at sea and more comfortable for crew and passengers. This type of configuration, however, is not self-stabilizing. The angle of attack on the hydrofoils must be adjusted continuously to changing conditions, a control process performed by sensors, a computer, and active surfaces. The first evidence of a hydrofoil on a vessel appears on a British patent granted in 1869 to Emmanuel Denis Farcot,

4845-467: The equation of motion can be written as d d x ( ρ v 2 2 + p ) = 0 {\displaystyle {\frac {\mathrm {d} }{\mathrm {d} x}}\left(\rho {\frac {v^{2}}{2}}+p\right)=0} by integrating with respect to x v 2 2 + p ρ = C {\displaystyle {\frac {v^{2}}{2}}+{\frac {p}{\rho }}=C} where C

4930-747: The equation, suitable for use in thermodynamics in case of (quasi) steady flow, is: v 2 2 + Ψ + w = constant . {\displaystyle {\frac {v^{2}}{2}}+\Psi +w={\text{constant}}.} Here w is the enthalpy per unit mass (also known as specific enthalpy), which is also often written as h (not to be confused with "head" or "height"). Note that w = e + p ρ       ( = γ γ − 1 p ρ ) {\displaystyle w=e+{\frac {p}{\rho }}~~~\left(={\frac {\gamma }{\gamma -1}}{\frac {p}{\rho }}\right)} where e

5015-464: The flow speed increases, it was Leonhard Euler in 1752 who derived Bernoulli's equation in its usual form. Bernoulli's principle can be derived from the principle of conservation of energy . This states that, in a steady flow, the sum of all forms of energy in a fluid is the same at all points that are free of viscous forces. This requires that the sum of kinetic energy , potential energy and internal energy remains constant. Thus an increase in

5100-427: The following simplified form: p + q = p 0 {\displaystyle p+q=p_{0}} where p 0 is called total pressure , and q is dynamic pressure . Many authors refer to the pressure p as static pressure to distinguish it from total pressure p 0 and dynamic pressure q . In Aerodynamics , L.J. Clancy writes: "To distinguish it from the total and dynamic pressures,

5185-413: The gas is sufficiently below the speed of sound , such that the variation in density of the gas (due to this effect) along each streamline can be ignored. Adiabatic flow at less than Mach 0.3 is generally considered to be slow enough. It is possible to use the fundamental principles of physics to develop similar equations applicable to compressible fluids. There are numerous equations, each tailored for

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5270-555: The hull are eliminated as the hull lifts clear, turbulence and drag act increasingly on the much smaller surface area of the hydrofoil, and decreasingly on the hull, creating a marked increase in speed. Early hydrofoils used V-shaped foils. Hydrofoils of this type are known as "surface-piercing" since portions of the V-shape hydrofoils rise above the water surface when foilborne. Some modern hydrofoils use fully submerged inverted T-shape foils. Fully submerged hydrofoils are less subject to

5355-401: The hydrofoil elements below the hull(s) develop enough lift to raise the hull out of the water, which greatly reduces hull drag . This provides a corresponding increase in speed and fuel efficiency . Wider adoption of hydrofoils is prevented by the increased complexity of building and maintaining them. Hydrofoils are generally prohibitively more expensive than conventional watercraft above

5440-1394: The irrotational assumption, namely, the flow velocity can be described as the gradient ∇ φ of a velocity potential φ . The unsteady momentum conservation equation becomes ∂ ∇ ϕ ∂ t + ∇ ( ∇ ϕ ⋅ ∇ ϕ 2 ) = − ∇ Ψ − ∇ ∫ p 1 p d p ~ ρ ( p ~ ) {\displaystyle {\frac {\partial \nabla \phi }{\partial t}}+\nabla \left({\frac {\nabla \phi \cdot \nabla \phi }{2}}\right)=-\nabla \Psi -\nabla \int _{p_{1}}^{p}{\frac {d{\tilde {p}}}{\rho ({\tilde {p}})}}} which leads to ∂ ϕ ∂ t + ∇ ϕ ⋅ ∇ ϕ 2 + Ψ + ∫ p 1 p d p ~ ρ ( p ~ ) = constant {\displaystyle {\frac {\partial \phi }{\partial t}}+{\frac {\nabla \phi \cdot \nabla \phi }{2}}+\Psi +\int _{p_{1}}^{p}{\frac {d{\tilde {p}}}{\rho ({\tilde {p}})}}={\text{constant}}} In this case,

5525-488: The late 1960s. However, the program was cancelled in the early 1970s due to a shift away from anti-submarine warfare by the Canadian military. The Bras d'Or was a surface-piercing type that performed well during her trials, reaching a maximum speed of 63 knots (117 km/h). The USSR introduced several hydrofoil-based fast attack craft into their navy , principally: The US Navy began experiments with hydrofoils in

5610-463: The law of conservation of energy , ignoring viscosity , compressibility, and thermal effects. The simplest derivation is to first ignore gravity and consider constrictions and expansions in pipes that are otherwise straight, as seen in Venturi effect . Let the x axis be directed down the axis of the pipe. Define a parcel of fluid moving through a pipe with cross-sectional area A , the length of

5695-572: The mid-1950s by funding a sailing vessel that used hydrofoils to reach speeds in the 30 mph range. The XCH-4 (officially, Experimental Craft, Hydrofoil No. 4 ), designed by William P. Carl , exceeded speeds of 65 mph (56 kn; 105 km/h) and was mistaken for a seaplane due to its shape. The US Navy implemented a small number of combat hydrofoils, such as the Pegasus class , from 1977 through 1993. These hydrofoils were fast and well armed. The Italian Navy used six hydrofoils of

5780-419: The neighbourhood of Paris ". This boat was designed by Comte de Lambert . This had 5 variable pitch fins on the hull beneath the water so inclined that when the boat begins to move "the boat rises and the planes come to the surface" with the result that "it skims over the surface with little but the propellers beneath the surface". The boat had twin hulls 18-foot long connected by a single deck 9-foot wide, and

5865-409: The other. When used as a lifting element on a hydrofoil boat, this upward force lifts the body of the vessel, decreasing drag and increasing speed. The lifting force eventually balances with the weight of the craft, reaching a point where the hydrofoil no longer lifts out of the water but remains in equilibrium. Since wave resistance and other impeding forces such as various types of drag (physics) on

5950-413: The parcel is d x , and the volume of the parcel A d x . If mass density is ρ , the mass of the parcel is density multiplied by its volume m = ρA d x . The change in pressure over distance d x is d p and flow velocity v = ⁠ d x / d t ⁠ . Apply Newton's second law of motion (force = mass × acceleration) and recognizing that the effective force on

6035-480: The pressure is lowest, and the lowest speed occurs where the pressure is highest. Bernoulli's principle is only applicable for isentropic flows : when the effects of irreversible processes (like turbulence ) and non- adiabatic processes (e.g. thermal radiation ) are small and can be neglected. However, the principle can be applied to various types of flow within these bounds, resulting in various forms of Bernoulli's equation. The simple form of Bernoulli's equation

6120-629: The relation of the potential to the flow velocity is unaffected by this transformation: ∇Φ = ∇ φ . The Bernoulli equation for unsteady potential flow also appears to play a central role in Luke's variational principle , a variational description of free-surface flows using the Lagrangian mechanics . Bernoulli developed his principle from observations on liquids, and Bernoulli's equation is valid for ideal fluids: those that are incompressible, irrotational, inviscid, and subjected to conservative forces. It

6205-515: The reservoir feeds) except where viscous forces dominate and erode the energy per unit mass. The following assumptions must be met for this Bernoulli equation to apply: For conservative force fields (not limited to the gravitational field ), Bernoulli's equation can be generalized as: v 2 2 + Ψ + p ρ = constant {\displaystyle {\frac {v^{2}}{2}}+\Psi +{\frac {p}{\rho }}={\text{constant}}} where Ψ

6290-475: The ships are running Sevastopol-Yalta and Sochi-Gelenzhik-Novorossiysk, with a Sevastopol-Sochi connection in the immediate plans in 2021. At the same time, the Alekseyev Bureau began building lighter, smaller Valday 45R  [ ru ] hydrofoils, based on a widely successful Polesye  [ ru ] model, at its own plant in Nizhny Novgorod, the relatively shallow-draft boats used on

6375-795: The shock. The Bernoulli parameter remains unaffected. An exception to this rule is radiative shocks, which violate the assumptions leading to the Bernoulli equation, namely the lack of additional sinks or sources of energy. For a compressible fluid, with a barotropic equation of state, the unsteady momentum conservation equation ∂ v → ∂ t + ( v → ⋅ ∇ ) v → = − g → − ∇ p ρ {\displaystyle {\frac {\partial {\vec {v}}}{\partial t}}+\left({\vec {v}}\cdot \nabla \right){\vec {v}}=-{\vec {g}}-{\frac {\nabla p}{\rho }}} With

6460-406: The speed of the fluid—implying an increase in its kinetic energy—occurs with a simultaneous decrease in (the sum of) its potential energy (including the static pressure) and internal energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ρ   g   h )

6545-690: The terms listed above: In many applications of compressible flow, changes in elevation are negligible compared to the other terms, so the term gz can be omitted. A very useful form of the equation is then: v 2 2 + ( γ γ − 1 ) p ρ = ( γ γ − 1 ) p 0 ρ 0 {\displaystyle {\frac {v^{2}}{2}}+\left({\frac {\gamma }{\gamma -1}}\right){\frac {p}{\rho }}=\left({\frac {\gamma }{\gamma -1}}\right){\frac {p_{0}}{\rho _{0}}}} where: The most general form of

6630-581: The top speed of even modern hydrofoils: cavitation disturbs the lift created by the foils as they move through the water at speed above 60 kn (110 km/h; 69 mph), bending the lifting foil. German engineer Hanns von Schertel worked on hydrofoils prior to and during World War II in Germany . After the war, the Russians captured Schertel's team. As Germany was not authorized to build fast boats, Schertel went to Switzerland , where he established

6715-871: The velocity field is constant with respect to time, v = v ( x ) = v ( x ( t )) , so v itself is not directly a function of time t . It is only when the parcel moves through x that the cross sectional area changes: v depends on t only through the cross-sectional position x ( t ) . d v d t = d v d x d x d t = d v d x v = d d x ( v 2 2 ) . {\displaystyle {\frac {\mathrm {d} v}{\mathrm {d} t}}={\frac {\mathrm {d} v}{\mathrm {d} x}}{\frac {\mathrm {d} x}{\mathrm {d} t}}={\frac {\mathrm {d} v}{\mathrm {d} x}}v={\frac {\mathrm {d} }{\mathrm {d} x}}\left({\frac {v^{2}}{2}}\right).} With density ρ constant,

6800-411: The water, deflecting the flow downward, which, following the Euler equations , exerts an upward force on the foil. This turning of the water creates higher pressure on the bottom of the foil and reduced pressure on the top. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle , so the resulting flow field about the foil has a higher average velocity on one side than

6885-607: The weather than traditional vessels, and Linda Line had a policy of cancelling departures when wind speeds exceeded 15 metres per second and/or wave heights were over 3 metres. In 2017, Linda Lines announced the delivery of a new vessel for 2018. Operations ended in November 2017, and Merilin and Karolin were sold off. The announced delivery of the new vessel was initially announced to be delayed. The company eventually filed for bankruptcy in May 2018. In 2008, Linda Line planned to purchase

6970-530: Was also helped by a decision made at the end of March to have the route depart from Linnahall terminal instead of Pirita. The line was operated by the small passenger ship Juku. At the beginning of 2010, the right to operate the route with Juku was granted to AS Kihnu Veeteed . Hydrofoil A hydrofoil is a lifting surface, or foil , that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes . Boats that use hydrofoil technology are also simply termed hydrofoils. As

7055-656: Was built in Feodosiya for the Dutch public transport operator Connexxion . Mid-2010s saw a Russian governmental program aimed at restoring passenger hydrofoil production. The Kometa 120M  [ ru ] , based on the earlier Kometa , Kolhida and Katran models, became the first to enter production, initially on Vympel  [ ru ] factory in Rybinsk, and later on More shipyard in Feodosiya. Since 2018,

7140-652: Was designed by Jim Brown. The Moth dinghy has evolved into some radical foil configurations. Hobie Sailboats produced a production foiling trimaran , the Hobie Trifoiler, the fastest production sailboat. Trifoilers have clocked speeds upward of thirty knots. A new kayak design, called Flyak , has hydrofoils that lift the kayak enough to significantly reduce drag, allowing speeds of up to 27 km/h (17 mph). Some surfers have developed surfboards with hydrofoils called foilboards , specifically aimed at surfing big waves further out to sea. Quadrofoil Q2

7225-408: Was fitted with a 14HP De Dion-Bouton motor, the boat was reported to have reached 20 mph. It was stated that "The boat running practically on its fins resembles an aeroplane". A March 1906 Scientific American article by American hydrofoil pioneer William E. Meacham explained the basic principle of hydrofoils. Alexander Graham Bell considered the invention of the hydroplane (now regarded as

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