How do the mainsail and the jib of a sailboat help the boat sail? What do these two sails have to do with force?
Since this is not my area of expertise, I searched Google under the key words "mainsail jib force" to get these possible sources:
http://www.usc.edu/CSSF/History/2006/Projects/J0126.pdf
(Broken Link Removed)
http://en.wikipedia.org/wiki/Sail
http://www.wb-sails.fi/news/470NewsAero/470Aero.html
http://www.barefootsworld.net/windwalker/aftmastsailingcalc.html
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.
I hope this helps. Thanks for asking.