The three factors improving efficiency using rudder bulbs are as follows:
1) Reduced hub vortex
2) Increased wake gain due to homogenized wake flow
3) Optimized interference between propeller and rudder
Improving efficiency by having a rudder bulb located near the propeller, the Ultimate Rudder has a rounded cap, allowing a configuration of the bulb as close as possible to the propeller.
Using a normal rudder, a strong hub vortex is produced from the propeller cap toward the port side of the rudder, causing energy loss, while the Ultimate Rudder is able to recover the vortex using the bulb head. This brings an increase in negative pressure at the rudder’s leading edge, leading to reduced rudder resistance, increasing hull efficiency through the use of the Ultimate Rudder.