The closed loop hydraulic drive of the propeller is highly efficient. Transmission efficiency from diesel engine to propeller is typically 80 to 82 percent at full load. It even increases at partial load. Half-load transmission efficiency is typically 82 to 85 percent. Since DP systems run at partial load most of the time, the partial load efficiency is of particular importance.
The hydraulic system acts as a vibration dampener. Propeller induced vibrations and engine induced vibrations are dampened by the hydraulic system and isolated from one another. There are no torsional or lateral critical speeds within the operating range of the equipment. The drive is extremely smooth.
Propeller speed is infinitely controlled through control of pump displacement. The DP computer accurately controls thruster output by comparing its electrical output signal to the pressure feedback signal from the hydraulic drive. Hydraulic pressure is directly proportional to propeller torque, so the feedback accurately represents delivered thrust, unlike speed feedbacks used on most older systems.
Hydraulic systems are extremely reliable, provided they are properly designed and the hydraulic fluid stays clean and cool. An appropriately sized heat exchanger on the power unit keeps the fluid cool while charge filters, return filters, and flushing filters keep the fluid at a high level of cleanliness. Pressurized breathers virtually eliminate air ingestion to keep the moisture out of the system.