The Towing Tank
A Towing Tank is an essential equipment of the Ship Model Basin, which is used to perform hydrodynamic tests for different ship models or other waterborne objects such as submarines, torpedoes and other underwater forms. It is basically an experimental equipment, which measures the different forces such as the drags on different ship models and predicts the performance of the models. A towing tank mainly measures the forces, especially the drag or resistance of a towed as well as self-propelled ship models.
The model consists of a basin or a tank, the dimension of which extends from a several meters in width to about a few hundreds of meters in length. The basin is constructed with a towing carriage that is made to run on two rails on either side of the tank. This towing carriage consists of computers and several devices which are responsible for controlling and registering the variable parameters such as speed, thrust and torque of propeller, angle of the rudder and many more to add to the list. The towing carriage either helps in towing the model or follows the self-propelled model and is responsible for performing resistance as well as the propulsion tests for towed and self-propelled ship models as well. The major portion of this test is to determine the amount of power should the engine provide, so as to reach the speed put forward in the contract, or more precisely between the owner of the ship and the shipyard. Moreover, the towing tank also helps in determining the behavior of the maneuvers in model scale. For this particular section, the self-propelled ship model is all exposed or set into a number zigzag maneuvers at different amplitudes of rudder angles, similar to Dieudonné spiral test or turning circles.
The image below shows the photograph of a typical towing tank and the tank shown in the figure is over 150 ft long, 11 ft wide and 5 ft deep and is located at the Hydromechanics Research Laboratory at the Purdue University
PPM & CPMC
You can also prepare a towing tank with a Planar Motion Mechanism (PMM) or a Computerized Planar Motion Carriage (CPMC), so as to measure the forces and moments of hydrodynamics on the ships or any other submerged objects that experience an influence of oblique inflow or enforced motions. A wave generator can be equipped in a towing tank and perform the seakeeping tests, This can be done either by the simulation of the natural or irregular waves or the model has to be exposed to a wave packet that produces a statistical set, also known as Response Amplitude Operators (RAO). RAO helps in determining the real life sea-going behavior of the ship in the sea with variable amplitudes and frequencies, these parameters are also known as Sea States.