Abstract: The present invention relates to sliding doors for closure of entranceways and to companionway entrance closure for watercraft in particular. A sliding plastic door panel is provided and the door panel, being translucent, admits light into the interior of a cabin area. The entire door assembly is mounted on the outside of a boat cabin and does not take up space in the cabin interior, but allows more usable cabin space within.Upper and lower plastic tracks are provided for movement of plastic roller trucks therein. The door panel, the two open tracks and the roller assembly are non metallic and non-corroding and the rollers do not require lubrication. The door panel and other parts do not require painting and provide a track and roller arrangement in which the weight of the sliding door panel is directed downward against the bottom of the track, and provides a sliding door that is smooth and easy to use in operation, and very attractive in appearance.