Editing Ship model basin (section)

== Test facilities ==
The hydrodynamic test facilities present at a model basin site include at least a [[towing tank]] and a [[cavitation tunnel]] and workshops. Some ship model basins have further facilities such as a maneuvering and [[seakeeping]] basin and an [[ice tank]].

=== Towing tank ===
[[File:UCL OTT.jpg|thumb|The Ocean Towing Tank - with both towing and wave making facilities - at [[University College London]]]]
[[Image:NewcastleTowingTank.jpg|thumb|A model being tested in the Towing Tank of [[University of Newcastle upon Tyne|Newcastle University.]]]]
[[Image:Berlin-tiergarten vws 20050404 p1020295.jpg|thumb|Cavitation tunnel of the Versuchsanstalt für Wasserbau und Schiffbau in Berlin]]
[[Image:Cavitating-prop.jpg|thumb|Cavitating propeller in a water tunnel experiment at the David Taylor Model Basin]]
A towing tank is a basin, several metres wide and hundreds of metres long, 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, respectively, variables such as speed, propeller thrust and torque, rudder angle etc. The towing tank serves for resistance and propulsion tests with towed and self-propelled ship models to determine how much power the engine will have to provide to achieve the speed laid down in the contract between shipyard and ship owner. The towing tank also serves to determine the maneuvering behaviour in model scale. For this, the self-propelled model is exposed to a series of zig-zag maneuvers at different rudder angle amplitudes. Post-processing of the test data by means of [[system identification]] results in a numerical model to simulate any other maneuver like [[Dieudonné spiral test]] or turning circles. Additionally, a towing tank can be equipped with a PMM ([[Ship motion test#Planar motion mechanism (PMM)|planar motion mechanism]]) or a CPMC (computerized planar motion carriage) to measure the hydrodynamic forces and moments on ships or submerged objects under the influence of oblique inflow and enforced motions. The towing tank can also be equipped with a wave generator to carry out seakeeping tests, either by simulating natural (irregular) waves or by exposing the model to a wave packet that yields a set of statistics known as ''[[response amplitude operator]]s'' (acronym ''RAO''), that determine the ship's likely real-life sea-going behavior when operating in seas with varying wave amplitudes and frequencies (these parameters being known as ''[[sea state]]s''). Modern seakeeping test facilities can determine these RAO statistics, with the aid of appropriate computer hardware and software, in a single test.

=== Cavitation tunnel ===
A cavitation tunnel is used to investigate [[propeller]]s. This is a vertical water circuit with large diameter pipes. At the top, it carries the measuring facilities. A parallel inflow is established. With or without a ship model, the propeller, attached to a [[dynamometer]], is brought into the inflow, and its thrust and torque is measured at different ratios of propeller speed (number of revolutions) to inflow velocity. A [[stroboscope]] synchronized with the propeller speed serves to visualize cavitation as if the cavitation bubble would not move. By this, one can observe if the propeller would be damaged by cavitation. To ensure similarity to the full-scale propeller, the pressure is lowered, and the gas content of the water is controlled.

=== Workshops ===
Ship model basins manufacture their ship models from wood or [[Paraffin wax|paraffin]] with a computerized [[milling machine]]. Some of them also manufacture their model propellers. Equipping the ship models with all drives and gauges and manufacturing equipment for non-standard model tests are the main tasks of the workshops.

=== Maneuvering and seakeeping basin ===
This is a test facility that is wide enough to investigate arbitrary angles between waves and the ship model, and to perform maneuvers like turning circles, for which the towing tank is too narrow. However, some important maneuvers like the spiral test still require even more space and still have to be simulated numerically after system identification.

=== Ice tank ===
{{main|Ice tank}}
An ice tank is used to develop [[icebreaker|ice breaking vessels]], this tank fulfills similar purposes as the towing tank does for open water vessels. Resistance and required engine power as well as maneuvering behaviour are determined depending on the ice thickness. Also ice forces on offshore structures can be determined. Ice layers are frozen with a special procedure to scale down the ice crystals to model scale.