Just an observation about battery capacity. I have a lot of interest in electric for cars and motorcycles, and the batteries are not where they need to be yet, true.

I am assuming a 30 ft sailboat:

For the space that you save by putting in an electric motor, and weight reduction, say 200lbs (based on an atomic 4 is about 350 w/fluids). How many 6v golf cart batteries could you wire in that space. I know with the size dimensions of my engine compartment I could probably rack 6 - 6v golf cart batteries @ 72lbs each 423lbs. So you gain about 200-250 lbs, of course now you don't have to carry fuel so subtract that weight and you aren't too much heavier.

Now with that much power - 1560 amp hours @12v based on

http://www.trojanbattery.com/Products/T-1456V.aspx
and looking at the speed to distance assumptions of the Vetus mentioned earlier in this post, you could get quite a good distance for minimal weight addition. I have 150-200lb friends so I will bring one less and it is a wash haha.

Then it really all goes back to charging, and if you are not a long distance cruiser you can most likely do it right at the dock. With shore power and that setup you could even use a golf cart charger/charging system.

Additionally I am currently setting up 4 of those batteries as my house bank which has 2 huge 12v monsters of the same relative size, but only 200 AH total. so there is an additional reserve 520AH, optimally of course, but engine starting battery becomes obsolete and there is space for 2 more.