In the merchant marine we typically concern ourselves only with surface lookouts scanning from the ship to the horizon for other maritime traffic. Additional types of lookouts would include low-sky lookouts and high-sky lookouts concerned primarily with air traffic.
When assigned to lookout duty, no other task may be performed. While the captain or mate may serve as lookout on a calm day with good visibility, the person fulfilling the role of lookout may never, under any circumstances, engage in maintenance or other duties which may have any possibility of distracting from their primary duty of looking out.
The number of lookouts varies with the number of personnel available and the work with which the vessel is engaged. Lookouts are assigned to three primary sectors: port lookout, starboard lookout, and after lookout.
The port lookout scans from just abaft the port beam to the bow, the starboard lookout scans from the bow to just abaft the starboard beam, and the after lookout scans behind searching for life rings marking a man fallen overboard in addition to any other objects. Each sector overlaps about 10 degrees to ensure no dead zones of vision.
A special watch, called the fog lookout, is stationed as far forward in the ship as possible and low down during fog or other conditions of poor visibility. The fog watch consists of two people. One with communications with the bridge; the other looks and listens.
The helmsman, lookout, and watch officer all do well to know how to use a compass to report sighted objects, report their position, and subsequently chart the location of those objects. While the standard compass, or a lighter hand bearing compass built for the purpose, may be used for this, lookouts will report sightings using relative bearings to the ship.
Using this system, the ship itself acts as the compass card, with the bow representing 000 degrees, the starboard bow 045 degrees, the starboard beam 090 degrees, the starboard quarter 135 degrees, and the stern itself as 180 degrees. The pattern continues around to the port side with the port quarter at 225 degrees and the port bow at 315 degrees.
The lookout is to report as soon as possible any sighting or suspicion of sighting, especially in times of fog or reduced visibility. Speed is key, and more eyes can be brought to bear on suspicions sooner when the lookout is encouraged to speak out.
The initial report will quickly and briefly explain what is sighted with as much detail in one or two words as possible. “Freighter” or “container ship” is fine, but so is “ship,” “power boat,” or “sailing vessel.”
Then comes the relative bearing, always relative to the ship, given as three digits, spoken digit by digit. The lookout may report a target as being on the bow, on the beam, so be familiar with the terminology used.
The range is then reported, if known. This value will be the most variable as it is very difficult to report distances at sea and all but the most experienced lookouts will give wildly varying and typically inaccurate guesses. It is still helpful to have some idea how urgent the sighting is. In closer quarters, lookouts can use the length of their own vessel as a measuring stick. The below descriptions give quick indications as to the level of potential navigational threat of the target:
Hull down – the ship is over the horizon, only the superstructure is visible.
On the horizon – the waterline of the ship is visible on the horizon.
Hull up – the ship is in from the horizon, the hull is now also visible.
Close aboard – the contact is reported as extremely close to own ship.
Finally the target’s movement is reported; if they are stationary, apparently stationary, in reverse, so forth.