here I have to correct you timothy: so called azimuth thrusters are not electrical but still connected to the engines mechanically. this is highly complicated and often faulty, but for example a lot of tugs use this setup with succes. I should do some research to say anything for larger ships, but it is certainly not impossible. the dutch johan de witt uses this, although not with that much succes, but I have often sailed on the westerschelde ferry koningin beatrix (http://www.shipbucket.com/images.php?di ... eatrix.png
) which has such an system.
also, it is not very complex to have fixed pods, but it is not often done on larger ships....... an 'podded' propulsion system is basically an Z-drive, which about all short keel sailing yachts have.
I could say more with some research, but homework is calling me back.