>>1773548Cruise-ships are largely diesel-electric because they need a lot of electricity outside of propulsion too, so they can flexibly get that from their gensets. The can also, for instance, just run on two out of four engines when fully power isn't needed.
With the power at hand here, a shiftable transmission is out of range. By far. Really far. So a mechanical drive means you have to follow the propeller-curve in the engine-speed/torque diagram. This can be really far from optimal and you can do nothing about it.
If you don't want a horribly expensive, fragile and energy intensive gearset you have to run a slow 2-stroke, which is HUGHE.
Diesel-electric also allows you to put the engines where you want. You don't need an enormous driveshaft going straight to the props. Often this is used, besides the obvious packaging optimization, for azipods, that can be rotated freely, making the ship way more maneuverable, which is beneficial for cruise-ships.
