The rudders are the main system of the entire movement and control of the ship. But we must not forget that the whole operation of the rudder depends on another key system called the steering gear. The steering gear integrated with the rudder system defines the complete turning mechanism required for each ship, regardless of size and type. The steering system is an indispensable part of the ship's equipment from the appearance of very early ships, which were operated manually to today's more sophisticated electro-hydraulic steering gears. The performance of the steering gear is determined by the basic requirements prescribed by the SOLAS Convention. Today, there are two main types of steering gear, namely a two- or four-cylinder hydraulic piston system and a hydraulic rotary vane steering gear. The piston system has two or four opposing hydraulic cylinders that rotate the rudder via a crosshead mechanism that converts the rectilinear motion of the pistons in the cylinders into a circular motion of the rudder. The rotary steering system works by introducing hydraulic oil under pressure to the compartments between the fixed stator vanes attached to the ship structure and the rotating rotor vanes attached to the rudder shaft. The hydraulic oil pressure in both systems is obtained by means of a electric driven hydraulic pump.Two types of pumps suitable for these steering gears are variable supply pumps with radial cylinders (hele-shaw) or pumps with axial cylinders and a swash plate. Both steering systems are accompanied by a piping system and a series of valves such as a safety valve and a control solenoid valve. Special attention must also be paid to the hydraulic oil as the performance of the steering gear depends on the temperature and viscosity of the hydraulic oil.