Being about the latitude of Barbados, we met an English frigate, or privateer, who first began to give us chase; but finding himself not to exceed us in strength, presently steered away from us. This flight gave us occasion to pursue the said frigate. As we did, shooting at him several guns of eight-pound carriage.
Thus reported Alexander Exquemelin in his Buccaneers of America, published in 1684. In the days before binoculars and sonar and the like, knowing what you were looking at out on the vast, open sea was not just handy but a matter of life and death. A ship like the American schooner Enterprise above might sail for weeks without spotting another. And since life at sea wasn't always full bellies and a good night's sleep, hungry, sleep deprived men had to be trusted to spot the enemy or - probably even more importantly - a prize.
As Exquemelin noted, the English privateer in question did not initially know what she was up against. As it turned out, the buccaneer ship was better armed and, in the end, faster than she was. Her initial impression, however, was of a fruit ripe for picking. How did freebooters in particular and any ship in general manage to avoid such situations? The answer in most cases was pure luck.
As we've seen in other posts, many navy ships and most raiders were not of local construction. A French privateer may have been built in Plymouth; an American sloop may have initially been a French privateer. The domino effect can easily be imagined. Trying to tell the nationality of your prey by build or set of sail was virtually impossible, at least until you got too close for reasonable comfort. And of course, her colors were of no use in identification.
Seeing another ship, particularly in fair weather, might be surprisingly easy if she had all her sail set. Pirates and privateers in the Northern hemisphere used the simple trick of staying to the south on a sunny day or even in a light haze. Particularly toward midday, the sun would hit the sails of the ship further north so that the glare would be unmistakable to a man in the tops on the southern ship. The opposite strategy (staying north to spy ships in the south) would work almost as well in the Southern hemisphere, with slightly different atmospheric conditions offering somewhat of a hindrance.
Giving chase could and many times would become a simple game of surprise. In the example above for instance, a well handled freebooter could stay just over the horizon for as long as he needed to, eyeing the sails of his prey while keeping his topsails reefed and his existence unknown. It's important to keep the spherical nature of our Earth in mind, something our ancestors understood far better than we give them credit for. The problem arose when the predator was the one surprised.
In inclement weather, chance meeting or complete misses were more likely. These conditions didn't help in the identification of your neighbor, either. William Dampier tells in his Voyages and Discoveries of sighting what he imagined was a convoy of Dutch merchants in a heavy mist. Upon sailing closer the mist lifted and he met, to his dismay, a flotilla of fifteen Dutch men-of-war. He beat a hasty retreat.
At night, things grew even worse from the standpoint of visibility. More than one log has noted that ships have, quite literally, passed in the night within one or two miles of each other without noticing. Ships were more likely to actually collide at night as well, one of the reasons that reducing sail in the late watches was the norm. The dark was the friend of the prey, as well. Dowsing all lights and changing course could save a ship from a larger or faster predator.
Of course that now famous Hollywood prop, the telescope, was available in some form aboard most ships. Known as a spy glass or simply a glass in English (or, in French, une lunette), this tool was more likely to be used to identify a ship once sighted than to find sail in the first place. Particularly for freebooters the instruments were fantastically expensive and dear even if taken in a raid. Dropping one from the tops would be a sin of the first order.
In the end, a ship - whether merchant, navy, privateer or pirate - would fare best with young, alert eyes in the tops. From there, more sober and experienced gazes could be consulted and the glass applied. Even then, mistakes were made. And one has to imagine that nothing stings quite like suddenly realizing you have gone from predator to prey.