cv and ep are two methods of creating curves, ep is with edit points which are points that lie on the curves surface and depending on where you places two of the points the tangent is decided. The CV curve is short for control vertex and its more like drawing the tangents of that curve, personally i prefer the cv curve as you get more control.
Just make your sail with a four sided curve that join up end to end, make a cloth object out of that and then constrain some of the cv's of that cloth object to your pole, maybe using locators for the joins. Ill post screens if you dont understand.
FX supervisor - double negative