The words you meet on a VHF course, in a coastguard notice or on a rescue-centre page — in plain English, each with its official source.
A
AIS — Automatic Identification System
A VHF system that automatically broadcasts a vessel's identity, position, course and speed to nearby ships and shore stations. Large ships must carry it, and many leisure boats fit it voluntarily. See also: MMSI, AIS-SART, AIS MOB device, VTSsource ▾International Maritime Organization (IMO) (2026-10-14): “Automatic identification systems (AIS) transponders are designed to be capable of providing position, identification and other information about the ship to other ships and to coastal authorities automatically.”
A personal beacon, often fitted to a lifejacket, that broadcasts the wearer's GPS position over AIS to vessels within VHF range, including their own boat. It is a locating aid with limited range, not a recognised way to alert the coastguard. See also: AIS, PLB, Man overboard (MOB), AIS-SARTsource ▾Maritime and Coastguard Agency (MCA), Personal Emergency Radio Devices leaflet (2026-10-14): “All devices using AIS have an inbuilt GNSS receiver which provides an accurate position so that rescuers can locate you more easily. The beacon will broadcast your position via AIS to any vessel that has an AIS receiver and is within VHF range.”
AIS-SART — AIS Search and Rescue Transmitter
A locating device for a liferaft or survival craft that broadcasts its GPS position as an AIS message, which shows on nearby AIS displays. It helps rescuers find you but does not itself alert a coastguard. See also: SART, AIS, AIS MOB device, Liferaftsource ▾U.S. Coast Guard (Marine Safety Advisory 01-22), via web.archive.org (2026-10-14): “The AIS-SART is a SAR transmitter used for locating survival craft. It may be used in lieu of the radar SART.”
B
Beaufort scale — Beaufort wind force scale
A 0–12 scale of wind strength based on observed sea conditions, used in marine forecasts. For example, Force 8 is a gale and Force 12 is hurricane force. See also: Gale warning, Shipping forecast, Small craft advisorysource ▾Met Office (2026-10-14): “The Beaufort scale, which is used in Met Office marine forecasts, is an empirical measure for describing wind intensity based on observed sea conditions.”
C
Call sign — Radio call sign
A unique set of letters and numbers issued with a ship radio licence and used to identify the vessel in voice radio calls. Many countries issue an MMSI with the call sign. See also: MMSI, VHF, MAYDAYsource ▾Ofcom (UK communications regulator), via web.archive.org (2026-10-14): “A ship’s radio call sign is a unique identifier that we assign to a ship when we first issue a Ship Radio Licence for it. An MMSI is a digital call sign and it, too, is unique to the ship to which we assign it.”
Channel 16 — VHF Channel 16 (156.8 MHz)
The international marine VHF voice channel for distress, urgency and safety calls and for first contact (hailing). After first contact, move to a working channel so Channel 16 stays clear. See also: VHF, MAYDAY, PAN-PAN, SÉCURITÉ, Channel 70source ▾Maritime New Zealand (Radio Handbook) (2026-10-14): “Channel 16 is the international VHF channel for maritime distress and hailing (calling).”
Channel 70 — VHF Channel 70 (156.525 MHz)
The VHF channel reserved for digital selective calling (DSC). A DSC radio uses it automatically to send distress alerts and digital calls. Voice is not allowed on it. See also: DSC, VHF, Channel 16, GMDSSsource ▾U.S. Coast Guard Navigation Center (NAVCEN) (2026-10-14): “VHF maritime channel 70 (156.525 MHz) is authorized exclusively for distress, safety and calling purposes using digital selective calling (DSC) techniques. No other uses are permitted.”
Coast radio station — Coast station
A shore-based radio station in the maritime radio service. Coast stations keep watch for distress calls, relay distress traffic and broadcast weather and navigation warnings. Many are run by the coastguard. See also: VHF, Channel 16, MAYDAY RELAY, NAVTEXsource ▾U.S. Code of Federal Regulations, 47 CFR 80.5 (FCC) (2026-10-14): “Coast station. A land station in the maritime mobile service.”
Cold water shock — Cold shock response
The body's automatic reaction to sudden immersion in water of 15°C or colder: a gasp, then rapid uncontrolled breathing and a jump in heart rate and blood pressure. It peaks in the first minutes and can cause drowning long before hypothermia sets in. See also: Hypothermia, Lifejacket vs buoyancy aid, Man overboard (MOB)source ▾RNLI, via web.archive.org (2026-10-14): “Cold water shock is the uncontrollable reaction of the body when it is first submerged in cold water (15°C or lower). In initial submersion, the body will experience a gasp reflex, which is a rapid intake of air.”
COLREGs — International Regulations for Preventing Collisions at Sea, 1972
The international 'rules of the road' at sea, covering steering and sailing rules, lights, shapes and sound signals. They apply to every vessel, including small leisure craft, on the high seas and connected navigable waters. See also: TSS, VTSsource ▾International Maritime Organization (IMO) (2026-10-14): “Rule 1 states that the rules apply to all vessels upon the high seas and all waters connected to the high seas and navigable by seagoing vessels.”
Cospas-Sarsat — International Cospas-Sarsat Programme
The international satellite system that detects and locates 406 MHz distress beacons (EPIRBs, PLBs and aircraft ELTs) and passes the alerts to rescue coordination centres. It is free for the person in distress. See also: EPIRB, PLB, RCC, GMDSSsource ▾International Cospas-Sarsat Programme (2026-10-14): “The International Cospas-Sarsat Programme is a satellite-based search and rescue (SAR) distress alert detection and information distribution system, best known for detecting and locating emergency beacons activated by aircraft, ships and backcountry hikers in distress.”
CROSS — Centre régional opérationnel de surveillance et de sauvetage
France's regional maritime rescue coordination centres (France's MRCCs). They can be reached on VHF channel 16 at sea or by calling 196 from the shore. See also: MRCC, Channel 16, SARsource ▾French Ministry of the Sea (mer.gouv.fr), via web.archive.org (2026-10-14): “Les Centres régionaux opérationnels de surveillance et de sauvetage (CROSS) disposent de deux moyens de contact d’urgence, le canal 16 de la VHF et le numéro 196, pour toute demande de secours en mer.”
A document some countries issue to visiting foreign yachts so they can cruise local waters for a set period without formally clearing in and out at every port. The rules, fees and eligibility differ by country; in the US it is called a cruising license. See also: Port of entry, Q flag, ICCsource ▾U.S. Code of Federal Regulations, 19 CFR 4.94 (U.S. Customs and Border Protection) (2026-10-14): “the port director will issue a cruising license in the form prescribed by paragraph (d) of this section permitting the yacht, for a stated period not to exceed one year, to arrive and depart from the United States and to cruise in specified waters of the United States without entering and clearing”
D
DSC — Digital Selective Calling
A digital radio feature that sends an automated distress alert, with your MMSI and GPS position, at the press of a button, and lets you call a specific station by its MMSI. After the alert, follow up by voice on Channel 16. See also: MMSI, Channel 70, VHF, GMDSS, MAYDAYsource ▾U.S. Coast Guard (Marine Safety Advisory 01-22), via web.archive.org (2026-10-14): “A radio equipped with DSC can generate a distress alert with vessel ID and position data, and an alert is relayed by other DSC-capable radios.”
E
EPIRB — Emergency Position-Indicating Radio Beacon
A vessel's 406 MHz distress beacon that alerts rescue centres through the Cospas-Sarsat satellites when activated. It can be switched on by hand, and some models start automatically on contact with water. It must be registered so rescuers know whose vessel it is. See also: PLB, Cospas-Sarsat, GMDSS, MMSIsource ▾International Cospas-Sarsat Programme (2026-10-14): “A 406-MHz beacon designed for use in an aircraft is known as an Emergency Locator Transmitter (ELT). One designed for use aboard a marine vessel is called an Emergency Position-Indicating Radio Beacon (EPIRB).”
Hand-held, parachute and smoke signals used to attract attention and show your position in distress. They have an expiry date and should only be fired in a real emergency. Some countries also accept approved electronic distress lights. See also: MAYDAY, Grab bag, Liferaftsource ▾Transport Canada (Safe Boating Guide, TP 511E) (2026-10-14): “When buying pyrotechnic distress flares, look for a Transport Canada approved stamp or label. Remember flares are only good for 4 years from the date of manufacture.”
Float plan — Float plan / trip plan / sail plan
A note of your boat, crew, route and expected return time left with a trusted person ashore. If you do not return on time, they know when to alert the rescue services and where searchers should look. See also: Passage plan, RCC, JRCCsource ▾Transport Canada (Safe Boating Guide, TP 511E) (2026-10-14): “A sail plan (also known as a trip or float plan) includes your planned route and describes your boat. No matter what you call the plan, you should file one before heading out – even if it’s only for an hour or 2.”
G
Gale warning — Gale warning
A marine warning that winds of gale force (Beaufort Force 8, about 34–40 knots) or stronger are expected or occurring in a sea area. See also: Beaufort scale, Shipping forecast, Small craft advisory, NAVTEXsource ▾Met Office (2026-10-14): “Gale warnings are issued as required throughout the day (for winds of Gale Force 8 or more). These are displayed with the Shipping forecast.”
GMDSS — Global Maritime Distress and Safety System
The international system of radio and satellite equipment and procedures for sending distress alerts and receiving safety information at sea. DSC radio, NAVTEX, EPIRBs and recognised satellite services are all part of it. See also: DSC, NAVTEX, EPIRB, Inmarsat / satellite distress, Cospas-Sarsat, Channel 70source ▾International Maritime Organization (IMO) (2026-10-14): “IMO and ITU implemented a new system to facilitate search and rescue radiocommunications at sea, the Global Maritime Distress and Safety System (GMDSS), which revolutionized the way distress, urgency and safety information was transmitted, coordinated and managed on a worldwide scale.”
Grab bag — Grab bag / ditch bag / abandon-ship bag
A watertight, easy-to-reach bag of emergency kit (for example a handheld VHF, PLB, flares, water and first aid) that you take with you if you have to abandon the boat. See also: Liferaft, PLB, Flares (pyrotechnics)source ▾Maritime and Coastguard Agency (MCA), Workboat Code Edition 3 (2026-10-14): ““Grab Bag” means an easily accessible, transportable and watertight bag or other portable container containing emergency supplies and equipment to aid survival in the event of an emergency evacuation of the vessel;”
H
Hypothermia — Dangerously low body temperature
A fall in core body temperature below 35°C, causing shivering, confusion, clumsiness and eventually unconsciousness. In cold water it develops over tens of minutes, after cold water shock, which is why a lifejacket matters. See also: Cold water shock, Lifejacket vs buoyancy aid, Man overboard (MOB)source ▾Transport Canada (Safe Boating Guide, TP 511E) (2026-10-14): “It can take an hour to go unconscious from hypothermia, even in ice water. Hypothermia occurs when your body’s temperature dips below 35°C.”
I
IAMSAR — International Aeronautical and Maritime Search and Rescue Manual
The joint IMO/ICAO manual that sets out how maritime and aviation search and rescue is organised and carried out. Volume III (Mobile Facilities) is the part carried on board ships. See also: SAR, RCC, SRRsource ▾International Maritime Organization (IMO) (2026-10-14): “the IMO and the International Civil Aviation Organization (ICAO) jointly develop and publish the International Aeronautical and Maritime Search and Rescue (IAMSAR) Manual, published in three volumes covering Organization and Management; Mission Co-ordination; and Mobile Facilities.”
ICC — International Certificate for Operators of Pleasure Craft
A certificate issued under UNECE Resolution 40 that shows, in a standard format, that you are competent to operate a pleasure craft. Some countries ask visiting skippers for it. Where it is accepted depends on the issuing country and the country you visit. See also: Port of entry, Cruising permitsource ▾United Nations Economic Commission for Europe (UNECE), via web.archive.org (2026-10-14): “provides the holder with evidence of competence for the operation of pleasure craft, in an internationally recognizable format, which can be presented to officials in foreign countries upon request.”
Inmarsat / satellite distress — Recognised mobile satellite services for GMDSS (Inmarsat and Iridium)
Satellite communication services approved by the IMO for sending distress alerts and receiving safety information beyond VHF range. Inmarsat and Iridium are the recognised providers. See also: GMDSS, Cospas-Sarsat, EPIRBsource ▾International Maritime Organization (IMO) (2026-10-14): “IMO has recognised Inmarsat and Iridium to provide satellite communication systems for use in the GMDSS.”
J
JRCC — Joint Rescue Coordination Centre
A rescue coordination centre that handles both maritime and aviation search and rescue from one place. Australia, Canada, Norway and the UK, among others, run JRCCs. See also: MRCC, RCC, SRR, SARsource ▾Australian Maritime Safety Authority (AMSA) (2026-10-14): “AMSA operates Joint Rescue Coordination Centre (JRCC) Australia. It has operational responsibility for SAR activities for international civil maritime and aviation.”
K
Kill cord — Engine cut-off switch (ECOS) lanyard
A lanyard or wireless link between the helmsperson and an engine cut-off switch. If the driver is thrown from the helm or falls overboard, the engine stops, so the boat does not keep running or circle back towards people in the water. See also: Man overboard (MOB)source ▾U.S. Coast Guard Boating Safety Division (2026-10-14): “When an operator is wearing a link while underway, the engine will cut-off if the operator is separated from the operating area, an occurrence that can happen if the operator is ejected from the vessel or falls within the vessel.”
L
Lifejacket vs buoyancy aid — Lifejacket and buoyancy aid (personal flotation devices)
A buoyancy aid gives some flotation for confident swimmers near help but will not turn an unconscious person face-up. A lifejacket (usually 150 N or more) is designed to turn the wearer onto their back with mouth and nose clear of the water. See also: Newton rating (50 / 100 / 150 / 275 N), Man overboard (MOB), Cold water shocksource ▾RNLI, via web.archive.org (2026-10-14): “A buoyancy aid has integral foam buoyancy. But it is not designed to turn a person the right way up, and so would not support an unconscious person in the water.”
Liferaft — Inflatable liferaft
An inflatable survival craft, usually packed in a canister or valise, that you board if the vessel has to be abandoned. It must be big enough for everyone on board and serviced regularly. See also: Grab bag, SART, AIS-SART, EPIRBsource ▾U.S. Coast Guard (A Boater's Guide to the Federal Requirements for Recreational Boats) (2026-10-14): “If you are planning to boat offshore or in an area where rescue is not close at hand, you may want to consider carrying a U.S. Coast Guard approved life raft. The life raft should be large enough for everyone on board.”
M
Man overboard (MOB) — Person in the water after falling from a vessel
When someone falls from a boat into the water. It is one of the main causes of boating deaths. Wearing a lifejacket, keeping the kill cord attached and practising recovery greatly improve the chances of survival. See also: AIS MOB device, Lifejacket vs buoyancy aid, Kill cord, Cold water shocksource ▾Transport Canada (Safe Boating Guide, TP 511E) (2026-10-14): “Falling overboard is one of the main ways people die while recreationally boating in Canada. Wearing your lifejacket and knowing what to do can reduce the risk of drowning.”
MAYDAY — Radiotelephone distress signal
The spoken distress signal, said three times, for grave and imminent danger to a vessel or person that needs immediate help. It has priority over all other radio traffic and may only be used in genuine distress. See also: PAN-PAN, SÉCURITÉ, MAYDAY RELAY, SEELONCE MAYDAY, Channel 16, DSCsource ▾Maritime New Zealand (Radio Handbook) (2026-10-14): “DISTRESS: the radio-telephone distress signal MAYDAY is used to indicate that a vessel, aircraft or person is in grave and imminent danger and requires immediate assistance.”
MAYDAY RELAY — Distress relay call
A distress message sent by a station that is not itself in distress, for example when the vessel in distress cannot transmit or its MAYDAY has not been answered. The relaying station gives its own call sign and then repeats the original distress details. See also: MAYDAY, Channel 16, RCCsource ▾U.S. Code of Federal Regulations, 47 CFR 80.324 (FCC) (2026-10-14): “A mobile station or a land station which learns that a mobile station is in distress must transmit a distress message in any of the following cases: (1) When the station in distress cannot transmit the distress message.”
MMSI — Maritime Mobile Service Identity
A unique nine-digit number that identifies a vessel or radio station in DSC calls and AIS signals. It must be programmed into DSC radios and registered so rescuers can see who is calling. See also: DSC, AIS, Call sign, EPIRBsource ▾U.S. Coast Guard Navigation Center (NAVCEN) (2026-10-14): “Maritime Mobile Service Identities (MMSIs) are nine-digit numbers used by maritime digital selective calling (DSC), automatic identification systems (AIS), and certain other equipment to uniquely identify a ship or a coast radio station.”
MRCC — Maritime Rescue Coordination Centre
A centre run by a national coastguard or SAR authority that receives distress alerts and organises the search and rescue response for vessels and people at sea in its area. Many countries run several MRCCs, each covering part of the national search and rescue region. See also: JRCC, MRSC, RCC, SRR, SARsource ▾HM Coastguard / UK Search and Rescue (GOV.UK) (2026-10-14): “HM Coastguard (HMCG) fulfils its responsibility for the initiation and co-ordination of civil maritime and aeronautical SAR around the UK through its fully integrated and flexible network of nine Maritime Rescue Co-ordination Centres (MRCC)”
MRSC — Maritime Rescue Sub-Centre
A smaller centre that works under a main rescue coordination centre and coordinates maritime search and rescue in a local part of its region. See also: MRCC, JRCC, RCC, SRRsource ▾Canadian Coast Guard (Notices to Mariners) (2026-10-14): “In addition, two Maritime Rescue Sub Centres (MRSC), staffed by Coast Guard Personnel are located in Québec, QC, and St. John’s, NL to coordinate local maritime SAR operations.”
N
NAVTEX — Navigational Telex
An automatic text broadcast on 518 kHz that delivers navigation and weather warnings, forecasts and urgent safety information to a dedicated receiver on board, out to about 200 nautical miles from the coast. See also: GMDSS, SÉCURITÉ, Shipping forecast, Gale warningsource ▾NOAA National Weather Service (2026-10-14): “NAVTEX is an international automated medium frequency (518 kHz) direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent marine safety information to ships.”
Newton rating (50 / 100 / 150 / 275 N) — Buoyancy performance level of a personal flotation device
The number on a lifejacket or buoyancy aid label is its minimum buoyancy in newtons. Roughly: 50 N is a buoyancy aid for swimmers near help, 100 N is for sheltered water, 150 N is for general coastal and offshore use, and 275 N is for extreme offshore conditions or heavy clothing. See also: Lifejacket vs buoyancy aidsource ▾U.S. Coast Guard Boating Safety Division (2026-10-14): “The number in performance Level Devices (Level 70) indicates the minimum buoyancy of the device. Buoyancy of Level Devices is measured in Newton (N). 70 Newtons equals 15.74 pounds of buoyancy.”
P
PAN-PAN — Radiotelephone urgency signal
The spoken urgency signal, said three times, for a serious problem that is not yet grave and imminent danger, such as engine or steering failure or a medical problem. It can be upgraded to a MAYDAY if things get worse. See also: MAYDAY, SÉCURITÉ, Channel 16source ▾Transport Canada (Small Commercial Vessel Safety Guide, TP 14070) (2026-10-14): “PAN PAN indicates a safety problem that does not require immediate assistance.”
Passage plan — Passage plan / voyage plan
Planning a trip before you set out: checking weather, tides, hazards, your boat's limits and your crew's ability. Under SOLAS Chapter V this applies to all vessels, including small pleasure craft. See also: Float plan, Tidal stream / tidal race, Shipping forecastsource ▾Maritime and Coastguard Agency (MCA), MGN 599 Amendment 1 (2026-10-14): “SOLAS Regulation V/34 (‘Safe Navigation and avoidance of dangerous situations’) concerns prior planning of your trip, more commonly known as a voyage or passage planning.”
PLB — Personal Locator Beacon
A small 406 MHz distress beacon carried by a person rather than fitted to a vessel. It is switched on by hand and alerts a rescue coordination centre through the Cospas-Sarsat satellites. See also: EPIRB, Cospas-Sarsat, AIS MOB devicesource ▾U.S. Coast Guard (Marine Safety Advisory 01-22), via web.archive.org (2026-10-14): “The PLB is a manually activated emergency alerting device operating in the dedicated 406.0 – 406.1 MHz distress band monitored by the International Cospas-Sarsat Programme.”
Port of entry — Port of entry
A port officially designated for customs (and usually immigration) clearance. When arriving from abroad, you normally have to report at, or clear in through, a port of entry before cruising further. See also: Q flag, Cruising permit, ICCsource ▾U.S. Code of Federal Regulations, 19 CFR 101.1 (U.S. Customs and Border Protection) (2026-10-14): “The terms “port” and “port of entry” refer to any place designated by Executive Order of the President, by order of the Secretary of the Treasury, or by Act of Congress, at which a U.S. Customs and Border Protection (“CBP”) officer is authorized to accept entries of merchandise”
Q
Q flag — Yellow 'Q' (quarantine) flag
The plain yellow signal flag 'Q', flown when arriving in a country's waters from abroad to show that the vessel has not yet cleared customs and health formalities. Keep it flying until you have reported to the authorities. See also: Port of entry, Cruising permitsource ▾HM Revenue & Customs (GOV.UK) (2026-10-14): “For journeys that you must report, you must fly the yellow ‘Q’ flag as soon as you enter UK waters (the 12-mile limit). Make sure the flag can easily be seen and do not take it down until you’ve finished reporting to customs authorities.”
R
RCC — Rescue Coordination Centre
The general term for a centre that receives distress alerts and either runs the search and rescue response itself or hands it to the authority responsible for that area. MRCC and JRCC are types of RCC. See also: MRCC, JRCC, MRSC, SRR, SARsource ▾Australian Maritime Safety Authority (AMSA) (2026-10-14): “As an international point of contact for Australian SAR, RCC receives distress alerts and either coordinates the response or transfers coordination to the responsible SAR authority.”
S
SAR — Search and Rescue
Finding and helping people in distress. At sea it is organised under the IMO's 1979 SAR Convention, so that a rescue is coordinated by a SAR organisation wherever an accident happens, with neighbouring countries cooperating when needed. See also: SRR, RCC, IAMSAR, GMDSSsource ▾International Maritime Organization (IMO) (2026-10-14): “was aimed at developing an international SAR plan, so that, no matter where an accident occurs, the rescue of persons in distress at sea will be co-ordinated by a SAR organization and, when necessary, by co-operation between neighbouring SAR organizations.”
SART — Search and Rescue (Radar) Transponder
A survival-craft device that, when triggered by a nearby ship's or aircraft's X-band (9 GHz) radar, shows a line of 12 dots on that radar screen pointing to your position. See also: AIS-SART, Liferaft, GMDSSsource ▾U.S. Coast Guard (Marine Safety Advisory 01-22), via web.archive.org (2026-10-14): “Once activated, the radar-SART listens for a 9 GHz X-Band radar signal and, when one is detected, transmits a response that is displayed by the triggering radar as a line of 12 dots”
SÉCURITÉ — Radiotelephone safety signal
The spoken safety signal (pronounced 'say-cure-ee-tay'), said three times, before a navigation or weather warning such as a drifting hazard or a gale. See also: MAYDAY, PAN-PAN, NAVTEX, Channel 16source ▾Maritime New Zealand (Radio Handbook) (2026-10-14): “SAFETY: the radio-telephone safety signal SÉCURITÉ (pronounced say-cure-ee-tay) is used to indicate that the calling station has an important navigational or meteorological warning to transmit.”
SEELONCE MAYDAY — Radio silence order during distress traffic
An order (from the French 'silence') telling all other stations to stop transmitting on a channel being used for distress traffic. 'SEELONCE FEENEE' means the distress traffic has ended and normal use may resume. See also: MAYDAY, MAYDAY RELAY, Channel 16source ▾Maritime New Zealand (Radio Handbook) (2026-10-14): “If necessary, the controlling station or the vessel in distress may impose silence on other stations in the area, using the signal SEELONCE MAYDAY, followed by its own name and callsign.”
Shipping forecast — Shipping Forecast (UK)
The Met Office marine forecast for the 31 sea areas around the British Isles, issued four times a day. It gives gale warnings in force, a general synopsis, and wind, weather and visibility for each area. See also: Gale warning, Beaufort scale, NAVTEXsource ▾Met Office (2026-10-14): “The shipping forecast is issued four times a day at 2300, 0500, 1100, 1700 UTC and covers a period of 24 hours from 0000, 0600, 1200 and 1800 UTC respectively. The waters around the British Isles are divided into 31 sea areas shown on the map.”
Small craft advisory — Small Craft Advisory (SCA)
A US National Weather Service marine advisory warning that wind or sea conditions may be hazardous to small boats. The thresholds vary by region, and the skipper decides whether their own boat and crew count as 'small craft'. See also: Gale warning, Beaufort scale, Shipping forecastsource ▾NOAA National Weather Service (2026-10-14): “An advisory issued by coastal and Great Lakes Weather Forecast Offices (WFO) for areas included in the Coastal Waters Forecast or Nearshore Marine Forecast (NSH) products. Thresholds governing the issuance of small craft advisories are specific to geographic areas.”
SRR — Search and Rescue Region
A defined area of sea (and airspace) for which one country has agreed to provide search and rescue services. The world's oceans are divided into SRRs, so every position at sea falls under a responsible rescue centre. See also: SAR, RCC, MRCC, JRCCsource ▾International Maritime Organization (IMO) (2026-10-14): “IMO's Maritime Safety Committee divided the world's oceans into 13 search and rescue areas, in each of which the countries concerned have delimited search and rescue regions for which they are responsible.”
A tidal stream is the horizontal flow of water caused by the rise and fall of the tide. A tidal race is a stretch, often off a headland or in a narrow channel, where strong streams make the sea fast and rough, worst when the wind blows against the tide. See also: Passage plan, Beaufort scalesource ▾Maritime and Coastguard Agency (MCA), MGN 599 Amendment 1 (2026-10-14): “At sea, changes in tidal streams could make conditions worse, particularly if the wind and tide are against each other.”
TSS — Traffic Separation Scheme
A routing system that separates opposing streams of shipping into lanes, like a dual carriageway at sea, in busy areas such as the Dover Strait. Rule 10 of the COLREGs sets out how vessels must behave in and near them. See also: COLREGs, VTSsource ▾International Maritime Organization (IMO) (2026-10-14): “Traffic separation schemes and other ships' routeing systems have been established in most of the major congested, shipping areas of the world, and the number of collisions and groundings has often been dramatically reduced.”
V
VHF — Very High Frequency (marine VHF radio)
The standard short-range marine radio for talking to coastguards, marinas and other vessels. It works roughly line of sight, so range depends on antenna height. Further offshore you need MF/HF radio or satellite communications. See also: Channel 16, Channel 70, DSC, MMSI, Coast radio stationsource ▾U.S. Coast Guard Navigation Center (NAVCEN) (2026-10-14): “Your VHF radio is intended mainly for short range communications, generally 5-10 miles, and at least 20 miles to a USCG station.”
VTS — Vessel Traffic Service
A shore-based service, usually at busy ports and waterways, that monitors shipping and gives traffic and safety information, sometimes directing traffic. Small craft should listen on the local VTS channel. See also: TSS, AIS, COLREGssource ▾International Maritime Organization (IMO) (2026-10-14): “Vessel traffic services (VTS) are shore-side systems which range from the provision of simple information messages to ships, such as position of other traffic or meteorological hazard warnings, to extensive management of traffic within a port or waterway.”
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