Towing tank

A towing tank is a long, straight basin of still water in which an instrumented carriage tows a scaled ship model to measure resistance and run propulsion, seakeeping, and maneuvering tests. Resistance tanks run from roughly 100 m to over 250 m so the model settles to steady speed within the measured length. The carriage holds the model on dynamometers, turbulence stimulators trip its boundary layer to turbulent, and a wavemaker at one end allows seakeeping work. Wave-making (residuary) resistance scales to the ship by Froude number; friction is corrected with the ITTC-1957 line. It is the physical counterpart of the numerical towing tank.