To send or signal SOS-MAYDAY is only to be used in the case of “grave and imminent danger to a vessel or persons, such as fire, sinking, man overboard etc.”
When you make a Mayday call, the “Search and Rescue” jumps into action. They direct massive resources across long distances to get to you as soon as possible – regardless of the risk and the cost. Therefore, Maydays must be reserved for truly life-threatening situations.
So serious is a Mayday call considered to be, that in many countries now anyone making a false Mayday call could be prosecuted under criminal law. It is solely intended to save lives.
A fire aboard
A capsized boat
Loss of engine or steering close to rocks in heavy sea
Taking on water more then pumps can handle
A medical emergency
Stormy weather that endangers boat and crew
If your situation is difficult — but not immediately life-threatening — choose a standard request for assistance instead.
If you’ve lost your navigation on board, try to use your mobile phone’s GPS-position and paper charts.