When the diesel engine is running, the clutch is engaged and drives directly the marine gear or transmission. Thanks to the PHT, the diesel engine also drives the electrical generator.
The electrical generator can generate, if not the axis will spin idle inside the generator. Due to the ratio (1.47 or 1.7) inside the PHT, we increase the rpm of the diesel engine at the PTO/PTI which allows us to reduce the electrical motor size.
The electrical generator generates electricity which can be used for on board equipment or for charging on board batteries, which can be used later to drive the electrical motor or on board equipment

The PHT in electrical mode disconnects the diesel engine by disengaging the clutch, thus the diesel engine can be shut down. The electric motor drives the marine gear or transmission directly through the PHT gears with a ratio (1.47 or 1.7) which decreases the electric motor rpm and increases the torque. The electric motor takes his power from a generator set or from on board batteries

In boost mode the clutch is engaged so the diesel engine is running. The electric motor is also running synchronised with the diesel engine and thus increasing the torque at the transmission or marine gear. The electric motor takes his power from a generator set or from on board batteries.
This way you can reduce diesel engine size when max power is only used for a short time or save fuel by running the diesel engine at limited power and adding power from the electric motor