There are many things to consider with the diesel-electric hybrid system you are contemplating. At around 12 HP, the 9K motor seems kind of small, but that's not my point.
For this system to make any sense at all, you:
1. Have a need to generate a lot of electricity.
2. Have a generator that is smaller than the capacity of the electric drive.
Regarding option 2. This is a sailboat. You can generate electricity while sailing via the drive. You can generate electricity via solar panels and / or wind generator. Your likely cruising speed will be some fraction of "full power" of the drive. That will allow you bursts of full power speed by pulling from the reserves of your battery.
If you actually charge your battery with the drive while sailing, solar panels, wind generator, etc. you could notice a significant drop in your fuel usage.
You should understand that if this is used as a system where you generate electricity with diesel to run your drive directly, you are only incurring more costs with little gain.
If I sound negative, I'm not. I just wanted to point some things out. I completely support the idea and I think you should research it more.
There is much discussion on the subject of electric generation and storage at fieldlines(dot)com. It is not a sailing site, but there is much to read on the subject of electricity generation and storage there.