A sharp-eyed lookout on the top of the main-mast of a British warship could see 12 miles on a clear day.  Before the unknown ship was hull-up on the horizon, he could see its sails from another two miles away.

An experienced seaman could tell from the cut and joining of the sails the origin of the vessel because each country made and joined sails differently in order to achieve the greatest power.  The lookout could tell a vessel by the “cut of its jib.”