There is LOTS of info on google for this. If you be a more specific of the info you need - I will be better equipped to help you. I have done one back in 2011 =)
It's no different from doing a contour profile on dry land.
http://geology.isu.edu/geostac/Field_Exe...
http://www.ehow.com/how_8508212_do-draw-...
Just grab a surf board and check out the chicks.