A user supported portable sail assembly and method uses the force of the wind to help propel a user on a mobile device such as skis, snowboards, skateboards, in-line or ice skates, for example, in a controlled and safe manner. A sail is attached to the ends of a pair of parallel, flexible poles which the user holds onto, usually one pole in each hand. The user orients the sail to optimize direction and speed. As the sail catches wind currents, the poles flex and form an optimal airfoil. Should the user wish to stop using the sail assembly, the user simply brings the poles together and brakes or glides to a gentle stop. The poles may be constructed of multiple interlocking segments for easy and quick disassembly and compact stowing.