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Denny Ship Model Experiment Tank

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Denny Ship Tank Building, 2009
Denny Ship Tank Building
© Lairich Rig

The Denny Ship Model Experiment Tank is located in Castle Street, Dumbarton, and was the first commercial testing tank of its kind in the world. It remains in active use, and continues to be used to carry out tests on models, and for the evaluation of new ship designs.

The innovative tank was was built in 1882, and is described as being as long as a football pitch at 300 feet in length, containing some 1.75 million litres of water. It has been restored by the Scottish Maritime Museum, which maintains it along with many other original features within the building it occupies, such as the clay moulding beds for casting wax models of ships' hulls, and the original Victorian machinery used to shape the models.

The tank is the last surviving part of the shipyard of William Denny and Brothers which operated from 1844 to 1963, who built every type of vessel ranging from sailing ships to modern liners. Dumbarton was notably home to many other famous shipyards, but these have all closed over the years.

The tank

Denny Ship Tank South, 2005
Denny Ship Tank South
© Lairich Rig
Denny Ship Tank, 2006
Denny Ship Tank
© Lairich Rig

An electrically driven gantry spans the width of the tank, and runs along its entire length. The tank is fitted with a wave generator which can be used to create many types of realistic scale sea conditions. The facility allow hulls, propellers, and rudders to be tested for efficiency at a variety of speeds and loads, and under varied operating conditions.

The wax models can be adjusted, and be fitted with different sizes and shapes of propellers and rudders to determine if these changes result in improved efficiency, speed, or fuel consumption. A minimum of ten minutes has to be allowed between consecutive runs in the tank, to ensure the water has settled and that initial conditions remains the same for each test.

For towed tests, the wax model is attached to the gantry using a rod and universal coupling fixed to the model's centre of gravity. This helps ensure the model display its natural movement through the water. Sensors gather data from the models and send this to instruments on the gantry.

For powered tests, electric motors are used to drive the propeller (or propellers) which power the model along the tank. In this case, the gantry is also powered along the length of the tank, and maintains the same speed along the tank as the model to avoid any drag from the wiring to the sensors.

The photographs show the two extreme ends of the tank: one taken at the north end, where visitors can look along the tank from the museum building, and the other at the south, (some 300 feet distant), which is not generally accessible.

Wax models

The wax models were made by referring to a set of scale drawings called offsets, supplied by the ship builder. From these drawings, shipwrights produced templates for the shape of the hull, and used the to create a female clay mould. Allowing for the wax to be two and a half inches A canvas covered framework was fitted inside the mould, spaced to ensure a 2.5-inch thick model hull would be produced when molten wax poured into the space between the clay and the canvas, and allowed to solidify.

The wax comprised a mix of 95% paraffin wax, 5% beeswax, and a small amount of Stearine added as a hardener.

Once set, the hull was removed from the clay mould and turned upside down. An operator used a stylus follow the lines on the offset drawings, and a pantograph apparatus fitted with two sharp paring blades simultaneously trimmed both halves of the hull identically to produce a smooth model of the hull which was to be tested. The model was then ballasted down to the required load line with steel shot.

Other experimental tanks

John Brown’s Shipyard at Clydebank also had its own tank where its hull and propulsion designs could be tested and fine tuned. However, this was demolished along with the rest of the yard, leaving only the iconic Titan crane standing as a tourist attraction after 2002.

The Admiralty maintained the Admiralty Research Establishment Glen Fruin, near Garelochhead, where torpedoes were tested. Although this was in use for many years after the war, it has lain largely abandoned for some years. Since the 1980s, buildings there have been closed, and become part of the Garlochhead Training Camp, used for FIBUA (fighting in a built-up area, known more commonly by troops as FISHing – fighting in someone’s house).[1]

Other shipyards rented facilities rather than incurring the cost of building their own.[2] The William Froude Laboratory at the National Physical Laboratory (NPL) Teddington, Middlesex, had at least two tanks in operation by 1936. One, The Alfred Yarrow Tank was built in 1911 after Sir Alfred Yarrow - who moved his ship building business from the Thames to Glasgow in 1908 - donated the sum of £20,000 for its construction. This tank was also described as being the length of a football pitch (specifically 550 feet long, 30 feet wide, and 12.5 feet deep at its centre), and could accommodate models of up to 20 feet in length, with the windows deliberately arranged to face north to ensure the Sun did not affect the temperature of the water, or the solidity of the wax. Had the wax heated and become soft, a waxy film could have formed on the surface of the water, and altered the dynamics of tests being repeated in the tank.

The second tank at NPL was known as the New Tank, and was installed to run from east to west, with the windows are arranged on the north side so that the sun would not affect the temperature of the water. This tank measured 678 feet long by 20 feet wide. Water at the east end is 9 feet deep for a distance of 446 feet. The floor of the tank then rises at a uniform rate for a distance of 36 feet to the shallow west end, where the depth remains at 2 feet to the end of the tank. This variation in depth allows the effects of shallow water on resistance and steering to be studied.

William Froude, 2011
William Froude
© Thomas Nugent

A memorial carving is set into the exterior the wall of the museum, together with an explanatory plaque dedicated to William Froude FRS LLD, whose Admiralty Tank built in Torquay in 1870 inspired the experimental ship testing tank which can be seen indoors.

Another Scottish link with the NPL came with the creation of the Lithgow Propeller Tunnel in 1935. High speed vessels such as destroyers and passenger liners could suffer a loss of power caused by cavitation, and together with the high forces placed upon their propellers, subsequent erosion of the blade surfaces cold result in frequent and expensive replacements being needed. The test apparatus was described as a vertical loop, although the sides were actually straight, standing 16 feet high and having a tunnel diameter of 3 feet. A powerful electric pump circulated the water within the tunnel while a window set in the test section allowed observation and photography of the propeller under test. Sir James Lithgow of Port Glasgow donated £5,000 to the project.

Location

Castle Street
Dumbarton
G82 1QS

Tel: 01389 763444

Email: [email protected]

Opening Hours: 10 am to 4 pm daily excluding Sunday.

Admission charges: Adult £2, Concession and Child £1.50, Family £5.

Please CHECK the above before travelling, as these details were noted in 2013.

References

1 Royal Marines’ X-men master the art of urban combat | Royal Navy Retrieved March 31, 2013.

2 HOW THE MODERN SHIP IS TESTED Retrieved March 31, 2013.

  • Shipping Wonders of the World No 1. 30 January, 1936.

External links

Related Canmore/RCAHMS and ScotlandsPlaces (SP) entries:-

 

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