I actually think diesel/electric is a reasonable way to go. At least under some conditions.
1) there is or needs to be a generator anyway
2) reduced power range is acceptable
3) the size of the house loads correlate reasonably to the propulsion demands (we don't want a 20kw generator running to power one AC)
4) little or no range expected from the batteries
5) propulsion requirements are minimal
In short I think it is possible, but doesn't meet many boats requirements since 3 and 5 are conflicting. The conversion is roughly 1hp=.75kw. So if your boat has a 20hp engine, you would need a 15kw generator to have the same power available at the throttle (ignoring conversion inefficiency). If you have a 40hp engine, which is pretty common on 40is footers you would be in the 30kw range.
First off, I've seen these systems in operation on motor cruisers (with large beer fridges!) and they certainly work and work very well - providing the added advantage of very short range propulsion to get to to anchor or out of the way should you happen to run out of fuel (don't ask!).
Your numbers seem about right to me - you'd have to expect that the diesel geneator would be about one or two sizes smaller than the diesel you pulled out. Don't forget that the generator control system will run the generator at it's optimum speed constantly
regardless of boat-speed - there's no need for the "peak power/extra revs" capacity you might normally have with a diesel installation because that can be supplied better by the batteries.
The only way electric power is if you can accept a pretty minimal range. Like just in and out of a harbor. For many day sailors this would work fine. But you would also loose the capability to make longer trips under power. I for instance would be fine with this system 99% of the time, but for a week or so a year we take the boat about 100 miles away for a distance race. I don't know that I would be willing to give up the capability to do this even if the rest of the time electric power would be fine.
Not necessarily. One thing is for sure, as your list indicates: The power system and all
components need to be correctly selected, designed, installed and commissioned by an experienced electrical engineer so that everything works together properly to meets the needs of a particular boat+owner - a diesel hybrid isn't something your average Joe Boatie (or even his regular Marine Mechanic) can put together without something going horribly wrong.
At the end of the day, similar to the diesel-hybrid system in a car, a diesel-hybrid system in a boat will cost more than a straight diesel but will also have a few advantages to make up for the added cost - depending entirely upon the selected installation and the way it's used.
Just imagine using thrusters instead of a conventional propeller/shaft? Or water jet?? For the first time since the propeller was invented, stern glands are no longer an essential part! With a hybrid system the possibilities are endless..
But for most
people, in most
places, with technology as it stands now, a hybrid is simply too complex to be worth the added cost/benefits - but that doesn't mean that, just like hybrid cars, it isn't the way of the future.