ers   |    Retrofit solution

Energy-efficient retrofit solution for shaft generator operation.

Slow steaming with strongly reduced service speed and operating constant-speed shaft generators at the same time at high efficiency are a contradiction. E-MS has a solution: E-RS – an energy-efficient retrofit system for conventional shaft generators.

Slow steaming means reduced service speed of a ship. In case the ship network for a diesel-mechanic driven ship is served by a shaft generator (PTO), the propulsion engine has to run on rated constant speed at all reduced load conditions but the most efficient slow steaming mode is to power the propeller on the „propeller curve“.

To gain the efficiency difference between these two modes, the shaft generator has to be switched off and auxiliary generating sets have to serve the ship network. By doing so, the operator has to take into account that auxiliary sets are less efficient than main engines, are using MDO instead of HFO and add to the maintenance costs. E-RS – the energy efficient retrofit solution solves this problem and enables the ship to operate at the highest efficiency possible at all times and operating conditions.

E-RS is using a power converter system providing power supply from the shaft generator at variable speeds without the need to run auxiliary sets.

The economic contemplation of the E-RS investment mainly depends on the running time and degree of slow steaming, the cost difference between the different kinds of fuel used and the fuel quality of the auxiliary generating sets. Calculations for existing ships have shown return on investments between one and two years.

Parallel operation of shaft generator and auxiliary sets is possible and the converter system can be combined with a bypass breaker to the existing plant, ensuring that known onboard operating modes remain available and can be utilized as before.


  • power supply from the shaft generator at variable shaft speeds under slow steaming operating conditions
  • maximum flexibility at all modes of operation – before and afterwards
  • shortest return of investments conditions
  • fuel savings of up to 15 % for the main engine with an efficient electrical power supply management
  • easy and cost-efficient implementation on ships in service without off-hire periods
  • there are no major adjustments necessary concerning power management and power distribution, thus only minimal changes of existing switchboard systems
  • minimized modification of main engine control