The main object is an almost-silent boat - electric drive is all-but silent and even if the generator is running it is highly silenced (to military grade.) The system should also be considerably "greener" compared to conventional diesel drive - for one of our favourite day-long 8 hour trips I have worked out the generator should only have to run for about 40 minutes to replace the charge used in the whole day.
How do I work this out? Well, not from complex tables of hull drag, propellor grip and other complex tables of figures I don't really understand and anyway don't know how to apply to our particular boat... but I don't need them!
For one thing I know the propellor grips the water very effectively because when I made a mistake (previously, with conventional engine in place) and left the propellor in gear at low revs I couldn't hold the boat against that force and took half the skin off my hand trying - luckily Jane was able to get on the boat at the other end to cut the motor! Luckily, also, we had suitable wound dressings on board.
For another, Jane and I have several times had to haul the boat by hand. But I know roughly how hard we can possibly pull, I know we got it up to walking pace (canal speed) in reasonable time and distance and then I can apply basic physics ... and hey presto what we actually did matches amazingly closely a totally theoretical sum of how much energy it takes to get the boat to walking pace in about the same distance and time.....
This is very good news, by the way, or the physics I have taught off and on all my life would be flawed!.....
Leaving out further details and the actual calculations, the fascinating thing is that my figures also show that we need an average power a bit under half a horse-power... in other words, the boat should ideally be hauled by a smallish, lazy horse. Odd that. Theoretical physics shows history is true!! Or... since James Watt worked out his value for 1 horse power from observing real horses, it shows that physics correctly predicts reality. Which is all it can do, and only if the theory is correct, but few people realise that.
So, the start of the future... for our to-be-electric narrowboat. About to generate and use exactly the same power as those horses did. So, is it the future or really just the same?