The normal service rating of the GIDE is determined by the power requirements for both propulsion during normal sea service, and the shaft generator to generate the electric power needed to drive the BOG injection compressors.
This system needs to burn a small amount of fuel oil as pilot fuel during gas burning. The excess BOG under slow steaming will be used by the shaft generator or the dual fuel auxiliary boiler in order to burn the gas and supply steam to the turbo generating system or dump condenser.
The LNG carrier is required to remain in standby condition during the cargo handling operations. Due to this, the maintenance of the main engine, such as dismounting the piston or inspecting and exchanging the fuel valve, is prohibited at that time. However if maintenance work of the main engine is necessary because of an accidental malfunction, the standby condition of the LNG carrier can be maintained by changing over the shaft generator to the emergency propulsion motor mode.
2.2.2 Twin Main Engine with Twin Screw (GIDE2)
The main particulars of the system are shown in Table 1. Typical engine room arrangement is shown in Fig.2.
The system configuration is nearly the same as that of the single main engine with single screw system. But, in this plant, emergency propulsion mode with turbo generator is not required. The vessel can maintain the standby condition by a single engine, should the other engine need maintenance work. Moreover, the twin controllable pitch propellers provide better maneuverability.