just like cars should be – none of this hybrid rubbish and extra complication.
The problem is the extra weight.
On a ship or a train the weight makes little difference as they (generaly) don’t have to deal with hills and gravity or have space constraints.
The closest road transport analogy would be a truck with 14 to 18 gears which lets them match the optimum engine RPM to road speed without the added weight/complexity of a hybrid system.
Also bear in mind “diesel” doesnt mean “internal combustion”, plenty of ships run on turbines (jet engines) which prodcue almost all their power at arround maximum RPM, which is useless for a propeller on a ship.