Time for action — using a NURBS surface to make the mainsail
You have used Subdivision Surfaces to model the sloop's hull and Bezier Curves to make the rudder and keel. Now you will use a NURBS (Non Uniform Rational B Spline) surface to make the mainsail:
Zoom out so you can see the whole sloop.
Press Shift+S and select Cursor to Center.
Put the cursor between the boom and gaff in the middle of where the sail will be.
Press Shift+A. Choose Add Surface then NURBS Surface.
Press R, Y, -90, Enter.
Press the Tab key
In the Properties window select the Object Data, it's the eighth button from the left.
In the 3D View, select one of the bottom control points of the NURBS Surface with theRMB.
In the Properties window, the Active Spline subpanel appears, check the checkboxes for Endpoint: U and Endpoint: V.
Press C and select the bottom row of control points. Press theRMB to finish the selection.
Move the selected control points near to the boom. Press A to deselect all of the control points.
Select and...