Seaspeak is an artificial dialect of English, adopted in 1988 by the International Maritime Organization of the UN for voice-over-VHF ship-to-ship and ship-to-shore communicaiton. It was developed in Britain in the early eighties as a codification of the de-facto English/French marine radio jargon. There's a carefully-chosen suite of standard messages, like weather forecasts and channel-choosing protocols, and an unusual system of explicit semantic tagging for custom messages.
Mayday! begin distress message
Pan-pan! begin urgent message
Sécurité! begin safety message
Coast Guard: Advice: do not overtake vessel ahead of you.
Vessel: I will not overtake vessel ahead of me.
Information: tanker stop in area Cod End Bank due to poor visibility. ("Stop" in the sense of "the tanker has stopped", not as in a telegram.)
Coast Guard: Question: what is your draft? ("What is" is optional.)
Vessel: Answer: my maximum draft seven meters.
My present speed 14 knots. Mistake. Correction, my present speed 12, one-two, knots. (To avoid confusion, "mistake" is the only way to indicate a mis-speech, and mistaken speech is not repeated, even to say "Not X, but Y". All mistakes must be followed by a correction.)
Seaspeak is closely related to Airspeak (the ATC language), trucker CB jargon, and police radio jargon; see also Q Codes and Basic English. The definitive reference is The Seaspeak Reference Manual, by Weeks, Glover, Strevens, and Johnson (Oxford: Pergamon, 1984).
http://www.xrefer.com/entry/443781 (not verbatim); US Coast Guard documents with names like "MSC/Circ.794"; my kitschy memory collection.