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37-478: The Underfall Yard is a historic boatyard on Spike Island serving Bristol Harbour in England. Underfall Yard was commonly referred to as "The Underfalls" and takes its name from the underfall sluices . The construction was completed in 1809 under the direction of William Jessop and substantially improved by Isambard Kingdom Brunel in the 1830s. Restored in the 1990s, Underfall Yard has been designated as

74-768: A lock to retain the water in the harbour; this was completed in 1809, and allowed ships to remain floating at all times, unaffected by the state of the tide on the river. Part of the project included building a dam at the Underfall Yard with a weir , known as the Overfall, to allow surplus river water to flow into the New Cut , an excavation which by-passed the Floating Harbour and joined the River Avon near Temple Meads . The docks' maintenance facility

111-524: A scheduled monument and from the 1970s onward many of the buildings at Underfall Yard have been given Grade II Listed Building status. The harbour and its equipment are still maintained, and house a number of maritime related companies. In the early nineteenth century the engineer, William Jessop was engaged by the Bristol Dock Company to create a Floating Harbour to eliminate the problem of ships being grounded at low tide. Jessop built

148-482: A Whitworth slotting machine, punching-and-shearing machines, a long-bed lathe and a steam hammer . There is also wall-mounted line-shafting and a Tangye horizontal engine and Cornish boiler . The former pattern-maker's shop and stores date from the same period and are grade II listed, Many of the original wooden patterns still exist with some being used for educational purposes, some being put on display, and others have been kept for operational purposes. The shop

185-415: A near-bed offshore sediment transport. These antagonistic flows may lead to sand bar formation where the flows converge near the wave breaking point, or in the wave breaking zone. An exact relation for the mass flux of a nonlinear periodic wave on an inviscid fluid layer was established by Levi-Civita in 1924. In a frame of reference according to Stokes' first definition of wave celerity ,

222-568: A predecessor built in the 1850s by boat builders Ross and Sage . It used a system in which the ship is floated onto the cradle and secured. The cradle is then drawn out of the water with a steam-driven winch . The device was a low-cost alternative to dry docks for maintenance and repair work. This became known as the Patent slipway or 'Heave-up Slip' and was patented in 1819 by shipbuilder Thomas Morton of Leith in Scotland. The 1890 replacement

259-448: A raised weight hydraulic accumulator which stores the hydraulic energy ensuring a smooth delivery of pressure and meaning that the pumps do not need to be running the whole time in order to satisfy peak demand. The external accumulator was added in 1954. The water is pumped from the harbour into a header tank and then fed by gravity to the pumps. The working pressure is 750 lbf/in² (5.2 MPa ). The dock maintenance workshops survive from

296-441: Is in the wave propagation direction. For small- amplitude waves, there is equipartition of kinetic ( E k {\displaystyle E_{k}} ) and potential energy ( E p {\displaystyle E_{p}} ): with E w {\displaystyle E_{w}} the total energy density of the wave, integrated over depth and averaged over horizontal space. Since in general

333-525: Is not open to the public. 51°26′48″N 2°37′03″W  /  51.4468°N 2.6174°W  / 51.4468; -2.6174 [REDACTED] Spike Island, Bristol Spike Island is an inner city and harbour area of the English port city of Bristol , adjoining the city centre. It comprises the strip of land between the Floating Harbour to the north and the tidal New Cut of

370-471: Is now The Pump House visitor centre. It is built of red brick with a slate roof and originally contained two steam engine powered pumps. These were replaced in 1907 by the current electrically powered machines from Fullerton, Hodgart and Barclay of Paisley (the currently installed electric motors were manufactured by JH Holmes & Co, Hebburn-upon-Tyne and date from 1938-9). It powered the docks hydraulic system of cranes, bridges and locks. The tower houses

407-458: Is now the visitor centre housed three boilers which powered steam hydraulic pumps. There are three electric pumps in the room adjacent to the visitor centre which are regularly run to demonstrate how they worked. These three pumps are 1907 replacements for the originals. Originally used as a place in which large items such as lock gates were built, the Big Shed was used by maritime businesses and

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444-508: Is occupied by RB Boatbuilding Ltd, a small business dedicated to the re-creation of classic, late 19th century, wooden working boats, including the Bristol Channel Pilot Cutter . The Slipway Co-operative Ltd manages the slipping of boats. They build, repair and restore wooden craft including the 14 feet (4 m) Bristol Jolly Boat . The original slipway was built by John Ward Girdlestone in 1890 which had replaced

481-476: Is onshore directed. This mass transport is localized in the upper part of the water column , i.e. above the wave troughs . To compensate for the amount of water being transported towards the shore, a second-order (i.e. proportional to the wave height squared ), offshore-directed mean current takes place in the lower section of the water column. This flow – the undertow – affects the nearshore waves everywhere, unlike rip currents localized at certain positions along

518-521: The River Avon to the south, from the dock entrance to the west to Bathurst Basin in the east. The island forms part of Cabot ward . The area between the Docks and New cut to the east of Bathurst Basin is in the neighbourhoods of Redcliffe and St Philip's Marsh . Spike Island was created by William Jessop in the early 19th century, when he constructed the New Cut and converted the former course of

555-400: The 1880s but were extended in the early 20th century. The brick building is topped with a tiled double-pile hipped roof with corbelled eaves. It has sliding doors at each end, giving access to the boiler and engine houses, blacksmith's and engineer's shops. Much of the original machinery survives, including steam-powered plant from the mid-1880s, these include a Whitworth planing machine ,

592-622: The River Avon into the Floating Harbour. Until the Second World War , a lock connected Bathurst Basin with the New Cut, and Spike Island was a genuine island surrounded on all sides by water. However, fears that an aerial attack on this lock at low tide could lead to a disastrous dewatering of the docks led to the lock being filled in. Historically, Spike Island was the site of working quays, shipyards, warehousing and other associated dockside industry. The Bristol Harbour Railway runs

629-479: The Slipway Co-operative and Underfall Trust in 1998–99. The restoration required the complete renewal of the underwater runway with steel piling to replace the previous timber, iron and masonry supports. The above-water track was re-laid, reusing the original cast iron centre rails with their integral ratchets . The cradle was completely rebuilt on the original pattern. The functioning of the slipway

666-420: The buildings and engineering installations at the yard were constructed between 1880 and 1890 under the direction of John Ward Girdlestone . Many of them have been designated by English Heritage as listed buildings . The octagonal brick and terracotta chimney of the engine house dates from 1888, and is grade II* listed, as is the hydraulic engine house itself. It replaced the original pumping house which

703-456: The common situation of zero mass flux towards the shore (i.e. Stokes' second definition of wave celerity ) – normal-incident periodic waves produce a depth- and time-averaged undertow velocity: with h {\displaystyle h} the mean water depth and ρ {\displaystyle \rho } the fluid density . The positive flow direction of u ¯ {\displaystyle {\bar {u}}}

740-587: The harbour railway across Spike Island is proposed for a £38 million rapid transit bus route from Ashton Vale to the city centre. The existing steam railway would be retained, but buses would gain a congestion-free journey into the city. Subject to planning permission and finances, work could start 2012 with services running 2014. [REDACTED] The following suburbs are in the same urban area, but lie in South Gloucestershire or North Somerset : Undertow (wave action) In popular usage,

777-689: The length of the island, and formerly connected these working areas with the railway network. With the redevelopment of the docks, the Island has become an area popular with developers looking to create prime dock side housing such as Baltic Wharf , The Point and Perretts Court . There are also a few restaurants and popular pubs such as The Orchard Inn and The Cottage . Other formerly dock-related buildings have become cultural venues or museums. These include: Other historic buildings have been converted into office space, housing small businesses and legal and financial companies such as Creditcall . The path of

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814-527: The management of the Underfall Yard Trust (previously Underfall Restoration Trust). Based at the yard are maritime academies, a scout sailing section, a blacksmith, rigging company, Omni, and three boat building businesses. In 2015 a major restoration project was announced with the work including the development of a cafe and visitor centre. An oral history project is being conducted and school education programmes have been introduced as part of

851-399: The mass flux M w {\displaystyle M_{w}} of the wave is related to the wave's kinetic energy density E k {\displaystyle E_{k}} (integrated over depth and thereafter averaged over wavelength ) and phase speed c {\displaystyle c} through: Similarly, Longuet Higgins showed in 1975 that – for

888-578: The more efficient modern 'Cutter-Suction' dredgers . During the 20th century the western parts of the yard were leased to P & A Campbell Ltd , operators of the White Funnel Line of paddle steamers as a maintenance base. The yards have been little altered recently except for the replacement of the three-storey 'A' block over the sluice paddle room resulting from bomb damage in World War II . Underfall Yard has been refurbished under

925-438: The potential energy E p {\displaystyle E_{p}} is much easier to measure than the kinetic energy, the wave energy is approximately E w ≈ 1 8 ρ g H 2 {\displaystyle {E_{w}\approx {\tfrac {1}{8}}\rho gH^{2}}} (with H {\displaystyle H} the wave height ). So For irregular waves

962-701: The required wave height is the root-mean-square wave height H rms ≈ 8 σ , {\displaystyle H_{\text{rms}}\approx {\sqrt {8}}\;\sigma ,} with σ {\displaystyle \sigma } the standard deviation of the free-surface elevation. The potential energy is E p = 1 2 ρ g σ 2 {\displaystyle E_{p}={\tfrac {1}{2}}\rho g\sigma ^{2}} and E w ≈ ρ g σ 2 . {\displaystyle E_{w}\approx \rho g\sigma ^{2}.} The distribution of

999-460: The restoration and redevelopment. In the early morning of 6 May 2023, the yard caught fire destroying several boats and a maintenance shed after a arson attack. Jessop's original designs for the harbour included a dam with an 'overfall', with the level of the water determined by the height of the dam's crest. As a result of the accumulation of mud and silt in the harbour, ships entering the narrow harbour were frequently being grounded. In 1832 Brunel

1036-825: The rip releases them. However, drowning can occur when swimmers exhaust themselves by trying unsuccessfully to swim directly against the flow of a rip. On the United States Lifesaving Association website, it is noted that some uses of the word "undertow" are incorrect: A rip current is a horizontal current. Rip currents do not pull people under the water—they pull people away from shore. Drowning deaths occur when people pulled offshore are unable to keep themselves afloat and swim to shore. This may be due to any combination of fear, panic, exhaustion, or lack of swimming skills. In some regions, rip currents are referred to by other, incorrect terms such as "rip tides" and "undertow". We encourage exclusive use of

1073-433: The shore. The term undertow is used in scientific coastal oceanography papers. The distribution of flow velocities in the undertow over the water column is important as it strongly influences the on- or offshore transport of sediment . Outside the surf zone there is a near-bed onshore-directed sediment transport induced by Stokes drift and skewed-asymmetric wave transport. In the surf zone, strong undertow generates

1110-405: The undertow velocity over the water depth is a topic of ongoing research. In contrast to undertow, rip currents are responsible for the great majority of drownings close to beaches. When a swimmer enters a rip current, it starts to carry them offshore. The swimmer can exit the rip current by swimming at right angles to the flow, parallel to the shore, or by simply treading water or floating until

1147-423: The water level, while sluice 3 ('deep') removes the silt. When the deep sluice is opened at low tide, a powerful undertow is created which sucks the silt out of the harbour and into the river. Since the original introduction of the sluices, they have been changed and renewed several times but today's sluice system was installed in the 1880s. In March 1988, the sluice control was computerised and automated. Most of

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1184-426: The word undertow is often misapplied to rip currents . An undertow occurs everywhere underneath shore-approaching waves, whereas rip currents are localized narrow offshore currents occurring at certain locations along the coast. An "undertow" is a steady, offshore-directed compensation flow, which occurs below waves near the shore. Physically, nearshore, the wave-induced mass flux between wave crest and trough

1221-427: Was called upon to provide the solution to this problem and designed the sluice system, still in use today, to remove excesses of silt and mud. In place of the Overfall he constructed three shallow sluices and one deep scouring sluice, between the harbour and the New Cut, together with a dredging vessel, known as a drag boat, to scrape the silt away from the quay walls. Sluices 1, 2 and 4 ('shallow') are used to control

1258-570: Was essential for the long-term preservation of the restored Underfall Yard as a historic industrial monument, as it provided the Underfall Restoration Trust with funds to maintain the slipway and buildings, and the tenants of those buildings with boats to earn a living. The power house at Underfall Yard was built in 1887 to supply hydraulic power to a network around the floating harbour. It was originally powered by steam (the large chimney remains from this system). The room which

1295-435: Was established on the land exposed by the damming of the river to construct the harbour, and remains sited at this location to the present day. By the 1830s the Floating Harbour was suffering from severe silting and Isambard Kingdom Brunel devised the underfall sluices based on William Jessop's original plans and recommended the use of dredgers as a solution . The Bristol Docks Company never achieved commercial success and

1332-409: Was originally driven by an hydraulic engine powered by the dock's hydraulic system. In 1924, an electric motor was installed which still operates today. The Bristol slipway is relatively small with a cradle of 100 feet (30 m) and a runway of 265 feet (81 m) and can lift vessels up to 250 tons (250 tonnes). It fell into disuse by 1974. By the 1990s this was rotting and was rebuilt by members of

1369-521: Was taken over by Bristol City Council in 1848. In 1880 the Council bought the Slipway and yard to enlarge the docks' maintenance facilities. The 'Underfall' system was re-built in the 1880s, with longer sluices, and the yard above was enlarged. Brunel's method of silt disposal is still in operation today, but the silt is carried in mud barges or pumped to the sluices through a quayside pipe system from

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