The term "man overboard" refers to a situation where someone has fallen in the water. When the warning is issued, any other boats in earshot should proceed with caution and anyone capable of doing so should assist in a rescue attempt. The individual that first sees someone in the water is typically advised to issue the man overboard warning, keep an eye on the distressed person, and help guide any rescuers. An international maritime signal flag exists for this emergency, which is red and yellow split diagonally from the top left to the bottom right. In some circumstances, a "pan-pan" emergency call may be made to alert nearby vessels that a rescue is in progress.
There are a variety of different ways that an individual can fall off a boat, resulting in a man overboard situation. Rough seas or high winds may combine with a slick deck and cause someone to lose their footing. On sailing ships, there is also the danger of a boom swinging around and knocking someone overboard. A man overboard situation can arise from bad luck, carelessness, intoxication, or may even be intentional.
If a member of a crew or a passenger can not be located, it may be assumed that they have gone overboard. In a situation such as this, all available hands may be asked to scan the surrounding waters for signs of the missing person. At other times, an individual may actually be witnessed going overboard. In this case, the witness should issue a man overboard warning, maintain a visual of the individual in the water, and continuously point at or indicate towards the distressed person. Keeping the person in sight can ensure he or she does not get lost in the waves, and pointing can help the ship captain maneuver in for a rescue.
Many vessels include a man overboard (MOB) function in their global positioning system (GPS). When activated, this feature can keep a record of the exact location that someone went overboard. The captain may then use that information to return to that location if visual contact is lost. Other systems include automatic functionality, where each crew member wears a device that will activate the MOB feature if it comes into contact with saltwater. This can create a record of where the person went overboard even if nobody saw it.
An internationally recognized signal flag can be hoisted to alert other nearby vessels that someone is in the water. In some circumstances, a "pan-pan" call will also be issued so that other ships know to proceed with caution. This warning can also alert other vessels that the rescue ship may have a restricted ability to maneuver for the duration. Nearby ships alerted through these means may provide assistance in the rescue operation or simply stay clear, as the situation requires.