A boat seat assembly having a seating platform including first and second seat bottoms and first and second seat backs, a seat mechanism for moving the seating platform between the flat position and the seating position, a base supporting the mechanism, and a positioning system for maintaining the seating platform in the seating position and for allowing the seat platform to move to the flat position. The seat mechanism includes a track and first and second sliders supported by the track for rectilinear movement for moving the seating platform between the seating position and the flat position. The positioning system includes a locking device for locking the first slider in various rectilinear positions relative to the track.