Pakistan Navy - Ship Model Towing Tank
A Towing Tank, also known as a Ship Model Basin or a model towing basin, is the equivalent of a wind tunnel for ships. A long, top-opened tank of a rectangular cross section equipped with a towing carriage that runs on two rails on either side. The towing carriage can either tow the model or follow the self-propelled model and is equipped with computers and devices to register or control speed, propeller thrust and torque etc.
China Ship Scientific Research Center [CSSRC] designed such a facility for a Pakistani institute. At the Pakistan Navy Operational Commands Seminar 2019, Chief of the Naval staff Admiral Zafar Mahmood Abbasi on 30 December 2019 expressed deep satisfaction over performance of the newly established Naval Research and Development Institute (NRDI) and appreciated progress made by NRDI in various projects. He also praised the collaboration of NRDI with local industry and academia and said that such interactions provide opportunities to seek long term joint ventures/ collaboration in various emerging naval systems and technologies.
Pakistan's dependency on China is understandable as Pakistan doesn't have expertise and resources to build Frigates & subs of local design. But if these are designed in house it will give PN much more flexibility which can be used to build bigger ships in future. The Marine Design Center has been established and a ship model basin was under construction. So local designs may emerge soon.
Working on model scale, the Basin is able, in advance of construction of a vessel, and at relatively small cost, to furnish a ship designer with a prediction of the performance of a vessel, to within a few percent. It is frequently possible for the designer in turn to make changes in the plans of the vessel which will improve the ship performance, and for the Basin to confirm the effect of these changes by inexpensive changes in the model, all before actual construction of the vessel or machinery has begun.
The ship models are first towed without propellers, and are then run under their own power with propellers, in a long basin of water which is sufficiently wide and deep to represent open sea. They are towed or guided by a large carriage which runs on rails laid on the walls of the basin, much as a traveling crane runs ak)ng rails secured to the walls of a shop.
Ben Franklin was perhaps the first constructor of a model towing basin. Riding on a canal boat in Holland, he observed that the horses had to pull harder when the vessel passed over the shallow sill of the canal locks. Franklin thought the shallowness must have something to do with it. On his return to America, he built a wooden trough, made a model boat, fastened it to a string which he passed over a wheel with a weight on the end, and worked out calculations which confirmed his belief. He had discovered an important principle in hydrodynamics. For many years, ship models for towing test purposes were made of wax but under modern conditions soft pine wood proved a much more satisfactory material.
A ship model test towing tank is a kind of hydrodynamic force experimental facilities; Generally can be used to carry out fluid dynamic experimental studies such as ship resistance and performance, sea-keeping, seaway load, ocean engineering, underwater robot and dynamic positioning technology, is the important experimental equipment of Naval Architecture and Ocean Engineering hydrodynamics teaching and scientific research. Due to the existence of the side walls in a towing tank, the measured hydrodynamic forces would present some discrepancies compared to the open sea results. This phenomenon is referred to as the side wall effect.
The Large Towing Tank of the private and independent Hamburg Ship Model Basin [HSVA - Hamburgische Schiffbau-Versuchsanstalt] has at Tank length: 300.00 meters, Tank breadth: 18.00 meters, and Tank depth: 6.00 meters. This enables such tests as: resistance, propulsion and tracking tests, horizontal planar motion testing, flow observation (paint and underwater TV), wake measurements (axial or 3-d laser velocimetry), propeller open water tests, seakeeping tests (in regular or irregular waves), measurement of forces and pressures acting on hulls or offshore structures, rolling tests, mooring tests.
The Laboratory of Ship & Marine Hydrodynamics at the National Technical University of Athens belongs to the Department of Naval Architecture & Marine Engineering. The Ship Model Towing Tank of the Laboratory, measuring 100 m x 5 m x 3,5 m, is unique in Greece and operational since 1979 at the Zographos campus.
The Robinson Model Basin at Webb Institute Maritime College houses a ship model towing tank and instrumentation room. The tank is used for student course work, academic instruction, consulting work, and U.S. Navy research. The single-rail towing tank is 93 feet long, including an eight-foot starting dock at one end. It is ten feet wide and five feet deep. Ship models can be towed and their resistance measured by suitable dynamometers up to speeds of 15 feet per second.
The Model towing tank of UK Defence Evaluation and Research Agency (DERA) is a 270m long, 12m wide and 5.5m deep wave-creating towing tank with deep and shallow docks. A planner motion mechanism can be utilised to measure the forces on a model travelling in a straight line or without superimposed yaw or pitch angles. The carriage can achieve a maximum speed of 12m/s and the wavemaker is the wet back, flat type, so capable of producing regular, random and/or rough sea breaking waves.
The Netherlands Ship Model Basin (now MARIN) is an internationally operating and recognised leading independent institution based in Wageningen with about 400 specialists who together realise a turnover of approximately €45 million. In 1873. Dr Bruno Johannes Tideman, chief engineer of the Royal Navy and adviser to the shipbuilding industry, carries out the first ship model tests in The Netherlands to determine the ship’s resistance and the required engine capacity. It is a professional challenge to make uncontrollable waves, wind and water ultimately manageable. The ‘Netherlands Ship Model Basin’ began its work in 1932.
The Tracor Hydronautics Ship Model Basin (HSMB) in Laurel MD is a water-towing facility 95 m long and 8 m wide, with a water depth of 4 m, Two independently powered carriage systems are used to propel models.
In the United States, the David Taylor Model Basin was built so that naval engineers could perfect their designs in the nautical equivalent of a wind tunnel. Testing of miniature models is a surprisingly important element in shipbuilding, and defense contractors have tested every Navy ship in this half-mile long tunnel prior to construction.
The David Taylor Model Basin is one of the largest of these testing facilities in the world. Intricately controlled waves are generated at one end by a pneumatic wavemaker, and absorbed on the other by a damper. The wavemaker can precisely simulate a range of weather conditions to assess performance on the open seas or in a hurricane force storm. A sliding platform that bridges the oblong pool moves with the models and gathers data using high speed cameras and sensors.
According to the American Society of Mechanical Engineers: “To meet requirements for uniformity … the rails on the basin walls upon which these carriages will run had to be far straighter and more level than the most perfect railroad track. In fact, to eliminate the effect of gravity on the motion of the towing carriage, the tracks are not straight in the usual sense, but follow the curvature of the earth.” The foundation of the building was laid directly on bedrock to ensure that the rails stay perfectly aligned.
The half-mile long pool is the largest at the David Taylor Model Basin, but there are also smaller ones specialized for certain tests. Shallow water, deep water, and turning pools help testers gather important data that they could not get in the high speed basin.
The basin’s predecessor was located at the Navy Yard. The 1896 Experimental Model Basin was state of the art in its time, but by 1910 flaws in its design were apparent. The riverside foundation was settling unevenly in the ground, and the nearby Anacostia occasionally flooded the facility. The David Taylor Model Basin, named for the engineer who designed the Experimental Model Basin, replaced it in 1940.
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