See the excellent tutorial from Ted Brewer:

Ted Brewer Presents A Primer on Yacht Design
The Numbers (More Than You Ever Wanted To Know!)
at: http://www.tedbrewer.com/yachtdesign.html

and more:

Sailboat Design Ratios by Dan Pfeiffer
http://dan.pfeiffer.net/boat/ratios.htm

Sailboat Design and Stability (/w online calculators)
http://www.sailingusa.info/design_winds.htm

Desin Notes by Steve Dashew (Click on indexed topics)
http://www.setsail.com/dashew/do_design.html
such as:
Stability and Comfort Design Factors by Steve Dashew
http://www.setsail.com/dashew/dashew215.html
Capsize Resistance
http://www.setsail.com/dashew/capsize.html

Understanding the Numbers - Basic design formulas for sailboats by Roger Marshall
http://www.boats.com/