Electric Sailboat

It seems you have two goals here, and I have to wonder which is the most important. The combination of an electric drive/charging generator is of course theoretically possible, but not practical for all of the reasons already given. However, if you want to use your IC diesel driven shaft and prop to auto-rotate (and charge a battery) while under sail then the simplest solution is to disengage the transmission and let the shaft drive an auxiliary generator connected to the shaft only via a belt configuration. It would be the same type of marine charging generator typically fitted to the front end of the diesel. It's not the most efficient method, but if you don't have a feathering prop and the shaft will be spinning anyway while under sail then it makes sense to take advantage of this small amount of lost potential. It's a relatively inexpensive compromise and has been proven to be sufficient for charging batteries.

 

Electricheater, You ought to check out the Yahoo Electric Boats group. Several people have done what you are considering. The archives will be an interesting read.

 

My 2 cents:

Please do as McDenny suggest with the Yahoo groups. A wealth of really good information.

My experience with electric powered boats:

I have a 1979 S2 11.0 (36 ft. 17,000 lbs) powered with 48 volt, (2 banks of 8 6v Trojan 105s.) Etek RT motor with a 1:25 reduction trans pushing a 12x7 "Perfect Pitch" prop with Navitas regeneration capable controllers.

Before powering the boat I read the many, many discussions about what was needed (what kind of motors, batteries, generators, solar panels, wind generators, chargers etc.) to make a particular size boat, with a particular shape and a particular weight traveling at x speed in x current and x wind, and how many watts, amps and volts were needed and would be optimum for this particular…., bla, bla, bla. I don’t want to take anything away from the theorist out there. God bless you for pondering all the many specifics and making an educated guess. (My father was an aeronautical engineer and was rather good at doing the same.) BUT, at the time I was ready to power my boat, I couldn’t find anyone who had actually COMPLETED a project with a boat anywhere near my size, put it in the water and had actual hard data. So I also made a guess.

Before I go further I want you to know I also have not collected any hard data yet. (my bad) I was more interested in sailing the damn thing than studying it.

My 2 cents: This set up works well as auxiliary power. (It is a SAILBOAT ya know) I’ve been out in 5 to 20 knots of blow on the Chesapeake Bay under power alone and this config pushed the boat along just fine. One day I motored all the way back home up the Magothy River (blew out the main on a particularly windy day) and was under power for at least 5 hours. I was drawing about 60 – 70 amps doing 3 to 5 knots. No problems and plenty of juice left when I got back to the slip.

Don’t worry about the regen part. If you are not hauling a$$ at 7 – 10 knots the regen ain’t going to work long enough to worry about over charging your batteries. If you are hauling a$$ for a really long period you may want to check the battery voltage and battery temp periodically. Check to see I if your controller monitors the regen. You can always motorsail to burn off any excess. Anyway, in my experience it has not been and probably will not be an issue for me.

One last note: I carry a portable 2500 watt Yamaha generator as a back up energy source in case I totally drain the batteries. (Theorist: please don’t yell at me about discharging the batteries more than 50% etc. Yes, yes, I know how bad it is for the batteries. I also studied the theories.) Worst comes to worst I can motor at about 2-3 knots using the generator alone or drop anchor and let the batteries charge for a bit or even wait for some wind.

I guess what I’m trying to say is study the theory, read the post and then build your self something. Keep in mind the real world doesn’t always work like the theory says it should. If you have an idea, give it a try. It may work better than you expect!

 

Here's a recently released cruising cat from African Cats which is what you're talking about. It bills itself as fossil fuel free, 100%. The term used to describe the propulsion system is "wind". Oh, and Moto-gens, which are retractable, obviating the need for folding or feathering props. The motors are run from 12 AGM batteries. . They've even gone so far as to put in an induction oven in the galley. No bio-fuels of any sort. Except, of course, in building it.

http://news.nauticexpo.com/press/african-cats/launch-green-emotion-20089-192407.html

 

Would be nice to know what that:

I have a 1979 S2 11.0 (36 ft. 17,000 lbs)

could be.
Why is everyone expecting all the world is familiar with the boat one self sails?

 

Ever heard of google?

try "s2 11.0"

Although an attached picture would be nice in the post, I agree.

 

1979 S2 11.0

Wow Apex1, I really didn’t think anyone would care that much about the boat I sail. I wasn’t try to write in code or anything.

1979 = year
S2 = company that makes the boat (yes that’s the whole name, the now defunct sailboat division of Slickcraft)
11.0 = the model # ( but also the size 11 meters or 36 feet)
17,000 lbs = weight in pounds (I think the official stats might have it as 15,000 pounds delivered but add some cruising equipment and it’s easy to arrive at 17,000 lbs)
I guess I should have mentioned in was a regular type mono hull.

Anyway, for the curious, here a few pictures.

My point wasn’t about the kind of boat I sail but the SIZE boat I electric powered and the data that wasn’t available.

At the time I could not find any hard data concerning a DIY (do it yourself) electric powered boat anywhere close to 36 feet and 17,000 pounds. According to some of the theorist this boat is too big to power the way I did and have any kind of decent performance and range. But I took a chance, made an educated guess and the boat does OK.