Of the things that I learned that stand out, an odd one is this:
Everyone knows the "Mayday" for emergencies. Fewer are aware that it is from the French m'aidez, "help me."
What I did not know was that there are two other "levels" of emergency calls:
In order of priority, mayday is the internationally recognized distress call that is used as preface in VHF radio transmissions only in situations in which there is an immediate danger of loss of life or the vessel itself. This includes when a boat is sinking, there’s a fire in the engine room, or someone on board is unconscious or experiencing a serious injury or illness.Source. Which has further information that is supposed to be included in a proper SOS message.
Pan-pan is the international urgency signal that is used as a preface to a VHF transmission when the safety of a person or the boat is in serious jeopardy but no immediate danger exists, but it could escalate into a mayday situation. For example, pan-pan is used in situations in which the boat has a slow leak or the engines are disabled and the boat is drifting toward a rocky shore.
Sécurité is a safety signal used as a preface to announce a navigation safety message. This may be an approaching storm, a navigation light failure, a submerged log in a harbor entrance or military gunnery practice in the area.
Hopefully, news you can't, and never can, use...