Guys, I have found some really good information about energy in a sail boat, batteries, alternators, different types of generators, electrical consumption...well the lot. I have already posted it in a small thread but I think that here is going to benefit more people. It is a book and you can download it.
Electricity on Board
by Reinout Vader
and it can be downloaded in the site of Victron Energy B.V.
, specialists in generators and energy.
Thanks to both to make this gem available on line.