In order to facilitate the removal of vessels from their berths at any wharf or place of mooring or for other reasons, the Harbor Master may direct the master or person in charge of any vessel to slack away hawsers, cables, or other fastenings of any ship and to stow booms or other rigging. Every vessel while backing out of any slip must have at least one member of the crew on the lookout astern on the upper deck, such person to be in full view of the pilothouse to warn the master, or the person in charge of such vessel, of the proximity of any obstruction to navigation or the approach of another vessel. Every vessel must continue to back a sufficient distance beyond the face of any pier to avoid any danger of accident or collision with any other vessel backing out from the same or any other slip. Every vessel backing out from a slip must proceed slowly, using extreme care for the prevention of accidents.