Marine Electric Drive Systems
Flexibility in machinery arrangements & in system operation have been long recognized attributes of electric drive systems. Such systems, which incorporate prime mover driven generators powering direct coupled or geared reversible propulsion motors would be particularly attractive in multiple shaft ships with many, or widely separated engines, or in advanced crafts, such as SWATHs (small waterplane area twin hull ships), where several sets of (right angle) bevel gearing would otherwise be necessary.
The ease with which electric systems can be reconfigured with switch gear could enhance survivability. Cross connection at cruise power levels (e.g. 1 engine powering 2 shafts), together with speed ratio control, can additionally permit propulsion engines to be operated at favourable load & speed conditions, an especially desirable feature with simple cycle gas turbines with poor part power fuel economy.
Offsetting these desirable features of electric transmissions has been their higher cost, increased complexity, lower transmission efficiency & greater weight & volume compared to mechanical drives.
The ease with which electric systems can be reconfigured with switch gear could enhance survivability. Cross connection at cruise power levels (e.g. 1 engine powering 2 shafts), together with speed ratio control, can additionally permit propulsion engines to be operated at favourable load & speed conditions, an especially desirable feature with simple cycle gas turbines with poor part power fuel economy.
Offsetting these desirable features of electric transmissions has been their higher cost, increased complexity, lower transmission efficiency & greater weight & volume compared to mechanical drives.
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