TITLE: Modelling forces acting on a sail
QUESTION [8 upvotes]: I'd like to create a basic model of the forces acting on a sail (wind sail, like a tail ship)
A couple of things I was thinking about: 
1) Can create a very simple model where wind is 'one' force acting on the a uniform body.
2) Model wind as vectors. This is where I am a little confused on how to start. 
3) Adding in multiple sails. 
4) I know that this would be a differential equation but after that I can't really see how it would be modelled. 
Any pointers? 
I'm not looking for someone to actually do the modelling for me, just a place to start. Like maybe some Wikipedia articles, etc.
Thanks

REPLY [2 votes]: When your analysis is on a simple basis where the sail can be modeled as a plane, the force will be perpendicular to the plane.  If you need a 3-D model of sail, it's more complex.
If you take what might be called the 20th century model in sailboat design, the force on the sail is resolved into a vector perpendicular to the approaching wind (lift) and a force parallel to the wind (drag). Likewise the forces on the hull are resolve to lift perpendicular to the direction of travel, and drag parallel to the direction of travel. You can find diagrams like this going back to Manfred Curry. 
I don't know about square riggers, but for the normal sloop rig, the jib and main interact too closely to consider them as independent. 
One math professor who wrote about sailing was c. stanley ogilvy. I wouldn't rush out to buy his books, but if you can find them in a library, you might find them interesting. The most widely available heavy duty treatments are by Marchaj (http://en.wikipedia.org/wiki/Czes%C5%82aw_Marchaj).