These guys have a good site:
Hybrid Propulsion
The bottom line is that by the time you are done it will probably cost the 10g plus, that a new diesel will cost.
- You will get maybe two hours between charges.
- You will have to be at a dock with shore power.
- It is louder than you might think because of the gearing.
- Long term costs will be higher than diesel as the batteries, a large part of the system cost, will have to be replaced every few years.
- I'm not sure of this but I suspect that maintenance or at least attention will be high as the systems are new.
- Resale value will likely be low.
The Catalina 27 is a good boat for this experiment, big enough to hold some batteries but an easy to drive hull.
I love the idea and plan on visiting "above the waterline" this winter.
A fully do-it-yourself setup may be cheaper but you will be inventing the engineering as you go.
I am very interested in this so if you want to go further call me or email, my contact info is in my profile page.