A rudder bulb is a flow rectification device installed on the rudder behind the   propeller hub, capable of achieving energy savings of 2% to 5%

The surface of the rudder bulb affects the viscosity of water flow, preventing   strong rotation of the water flow passing over the surface of the rudder bulb,   thereby achieving flow rectification. Additionally, the rudder bulb fills the   space behind the propeller, helping to weaken the low-pressure area at the   axis behind the propeller and thus reducing cavitation.