Re Electric Main Engine with a gen set.
There's been a couple of recent articles in one of the Brit sailing mags - it was either Yachting World or Yachting monthly - where someone has had this set up built into a new cruising yacht.
It may be worth getting hold of the magazine or a copy of the article - you could try on the publishers web site www.ybw.com
Whilst the set up did include a larger battery bank than one would normally carry, the principal idea was not
to run the main electric motor from the batteries all the time. To power along they aim to run the gen set (a small diesel) which then directly powered the main electric motor - with apparently better results overall than using a main deisel.
The article explained that the torque possible from the elctric motor at lower speeds was far greater than possible with a combustion engine. The fuel consuption of the small gen set used to drive the electrics wso cruising range under power multiplied several times. The overall weight was reduced. The costs were lower. Space was gained. The gen set was whisper quiet in operation - and one gets the benefit of the small gen set to also power 110v / 220v appliances if they are required.
I'm not sure if the boat is completed or still under contruction - but I do recall the owner had not completely filled in the original engine room space - just in case it did not work out as he planned!
Hope this is useful.