Andre wrote:
This large hollow tree undergoes the deformation of the boat in the waves and many problems with the bearings,
This requires a reduction gearbox often with high pressure and low pressure turbines, some diesel a fairly complicated reverse system
With an engine that drives an alternator, and two nacel engines at the back of the boat
This allows the engine and alternator to be placed in the center position of the boat.
the weight of the alternator is less than the mechanical transmission
less expensive electrical wiring lighter than the shaft with its bearings
No need to have a variable pitch propeller, the engine torque is well defined with the current (Drive AC).
The shaft transmission system is very reliable, the stages seem to me to be in cupronickel (integrated lubricator), never any problem for example on the French aircraft carriers Clemenceau and Foch (steam turbine engines), nor on the ex. France whose trees measure almost 100m. On the other hand, indeed it is heavy, but the deformations are limited because today the diesel powered cargo ships have the machine at the rear so short shaft and those which have a central machine are very rigid because they are not cargo ships.
Nacelle motors are an interesting solution, but not without drawbacks related to their drag, possible sealing problems and their greater exposure to shocks (like a Z-drive on a smaller boat)
On the new Queen Mary built in St Nazaire, the motors on the nacelle, 4 in number, are mobile on their axis at the rear (fixed on the front seems to me), but the propellers are always with variable pitch , which as you know is not only a question of engine torque, but also speed related flow
New diesel electric locomotives (100% electric operation on electrified line), moreover produced by Bombardier (in Europe) equip the few rare French lines whose electrification is not total, which previously required a change of engine. ..
