VHF Channel Assignments — Exam Reference
Know these channels cold. The USCG exam tests channel assignments repeatedly — especially Channels 16, 22A, 70, 13, and 9.
International Distress, Safety & Calling
Exam Tested156.800 MHz
Required watch channel — all vessels keep a continuous watch while underway
USCG Primary Working Channel
Exam Tested157.100 MHz
Shift here from Ch 16 when directed by the Coast Guard; used for MSI broadcasts
Recreational Calling Channel
156.450 MHz
Alternative calling channel for recreational boaters; bridge-to-bridge on some bridges
Bridge-to-Bridge / Navigational
156.650 MHz
Required on commercial vessels; 1 watt maximum; used for passing agreements
Intership Safety
156.300 MHz
For safety communications between ships; used with SAR aircraft on scene
Digital Selective Calling (DSC) Only
Exam Tested156.525 MHz
No voice permitted — digital distress alerts only; USCG monitors continuously
NOAA Weather Radio
162.550 MHz
Most areas; continuous NOAA weather broadcasts; receive-only
NOAA Weather Radio
162.400 MHz
Coverage varies by region; receive-only
Recreational Working Channels
Various
Non-commercial intership; marina and yacht club communications
Distress Signal Priority — MAYDAY, PAN-PAN, SECURITE
These three signals have strict, legally-defined meanings. Using the wrong one — or upgrading too slowly — can cost lives. The exam tests all three.
MAYDAY
Pronounced: MAY-DAY
Distress PriorityGrave and imminent danger — immediate assistance required
- ▸Vessel sinking
- ▸Fire aboard
- ▸Life-threatening medical emergency
- ▸Person actively drowning
PAN-PAN
Pronounced: PAN PAN
Urgency PrioritySerious situation — assistance needed but not immediately life-threatening
- ▸Person in water (conscious, afloat)
- ▸Engine failure in hazardous area
- ▸Person with serious injury, vessel mobile
- ▸Vessel aground but crew safe
SECURITE
Pronounced: say-CURE-ee-tay
Safety PriorityImportant navigational or meteorological warning for all vessels
- ▸Hazard to navigation (debris, unlighted buoy)
- ▸Severe weather bulletin
- ▸Floating container or obstruction
- ▸Shoaling or changed depth
Key exam rule: All three signals are initiated on Channel 16. Signals are spoken three times consecutively at the start of each call ("MAYDAY MAYDAY MAYDAY", "PAN PAN PAN PAN PAN PAN", "SECURITE SECURITE SECURITE"). After initial response on Ch 16, the Coast Guard may direct communications to Channel 22A.
MAYDAY Call — Correct Format
Step-by-Step Transmission
Transmit on Channel 16 at maximum power (25 watts). Speak clearly and slowly.
If no response: wait 2 minutes, reduce to 1 watt, try again. Then switch to Channel 22A or 2182 kHz (MF/HF).
DSC Distress Alert — Channel 70
- ▸Send DSC alert first — lift cover and hold distress button 5 seconds
- ▸Alert automatically includes MMSI and GPS position
- ▸Radio auto-switches to Channel 16 after sending
- ▸Transmit voice MAYDAY on Ch 16 immediately after
- ▸USCG and nearby vessels receive the digital alert within seconds
- ▸Never transmit voice on Channel 70 — digital data only
Acknowledge a MAYDAY
[Vessel in distress] MAYDAY
THIS IS [your vessel name]
RECEIVED MAYDAY
[Your position]
[ETA / assistance you can provide]
OVER
Silence, MAYDAY: To clear a channel of traffic during a MAYDAY: transmit "SILENCE MAYDAY" (SEELONCE MAYDAY) on Ch 16. Only the USCG or vessel in distress may impose radio silence on the distress frequency.
Radiotelephone Prowords — Procedures
Standardized prowords ensure clear, efficient radio communication. The exam tests the difference between OVER and OUT, ROGER and WILCO, and why you never say "REPEAT."
| Proword | Meaning & Use |
|---|---|
| MAYDAY | International distress signal — grave and imminent danger, immediate assistance required |
| PAN-PAN | Urgency signal — serious but not immediately life-threatening; vessel or person needs assistance |
| SECURITE | Safety signal — navigational or meteorological hazard affecting all vessels in the area |
| OVER | Transmission complete — a response is expected |
| OUT | Transmission complete — no response expected; conversation is ended |
| ROGER | I have received and understood your last message |
| WILCO | I understand and will comply with the instructions received |
| SAY AGAIN | Repeat your last transmission (never use 'REPEAT' — artillery fire command) |
| BREAK | Indicates a pause or separation between distinct parts of a long message |
| STANDBY | Wait — I will call you or respond shortly |
| AFFIRMATIVE | Yes / confirmed |
| NEGATIVE | No / not confirmed / that is incorrect |
Never say "over and out." OVER means you expect a reply. OUT means the conversation is finished. They are mutually exclusive. Using both together indicates you don't know proper radio procedure — and the exam will test exactly this.
VHF Watch Requirements
Who Must Monitor Channel 16
- ▸All vessels equipped with a VHF radio while underway
- ▸Watch must be continuous — not just when transmitting
- ▸Exception: when using radio on another channel (use dual-watch if available)
- ▸Vessels in U.S. waters must monitor Ch 16 (47 CFR 80.148)
- ▸Commercial vessels 20m+ must also monitor Ch 13 (navigational)
Power Output Rules
- ▸25 watts: Normal maximum VHF output — for distress and general use
- ▸1 watt: Required for bridge-to-bridge on Ch 13 (maximum permitted)
- ▸1 watt: Use low power in ports, marinas, and locks — minimum necessary power rule
- ▸FCC requires use of minimum power necessary to maintain communications
- ▸USCG recommends 25 watts for distress transmissions — maximum range
NATO Phonetic Alphabet
Used to spell out letters, vessel names, positions, and waypoints to avoid misunderstanding over radio. Numbers are spoken as: Zero, One, Two, Three, Four, Five, Six, Seven, Eight, Nine.
A
Alpha
B
Bravo
C
Charlie
D
Delta
E
Echo
F
Foxtrot
G
Golf
H
Hotel
I
India
J
Juliet
K
Kilo
L
Lima
M
Mike
N
November
O
Oscar
P
Papa
Q
Quebec
R
Romeo
S
Sierra
T
Tango
U
Uniform
V
Victor
W
Whiskey
X
X-ray
Y
Yankee
Z
Zulu
Numbers Over Radio
Speak each digit separately: 156.800 = "One Five Six Decimal Eight Zero Zero." The decimal point is spoken as "Decimal" or "Point." Never group numbers as you would in everyday speech.
Exam Tip — Common Phonetics Tested
Lima (L), November (N), Oscar (O), Quebec (Q), and Yankee (Y) are most commonly missed. Foxtrot vs. Tango and Sierra vs. Sierra/Seven confusions appear on exam questions about proper spelling.
FCC Ship Station License & Operator Requirements
Ship Station License (FCC Form 605)
Required when the vessel:
- ▸Travels to a foreign port
- ▸Is a documented U.S. vessel in international waters
- ▸Carries more than 6 passengers for hire on international voyages
- ▸Is required to be fitted with a radio by U.S. law (GMDSS vessels)
- ▸For domestic-only vessels: not required but the license must be aboard when required
Operator License Requirements
- ▸Restricted Radiotelephone Operator Permit (RP): minimum required for VHF on domestic voyages; no exam required
- ▸Marine Radio Operator Permit (MROP): required for international voyages; exam required
- ▸GMDSS Radio Operator License: required to operate full GMDSS equipment on SOLAS vessels
- ▸License must be in the operator's possession while operating the radio
- ▸Ship Station License must be posted or readily accessible aboard
MMSI Registration
To use the DSC distress function, you must have an MMSI programmed into the radio. Vessels required to have an FCC Ship Station License get their MMSI through the FCC (included on the license). Recreational vessels not required to be licensed can register for a free MMSI through BoatUS Foundation, Sea Tow Foundation, or the USCG. The MMSI is a 9-digit unique identifier — U.S. recreational vessel MMSIs begin with "338".
Digital Selective Calling (DSC) & GMDSS
DSC — Channel 70
- ▸DSC operates exclusively on Channel 70 (156.525 MHz)
- ▸No voice transmissions permitted on Ch 70 — digital protocol only
- ▸Distress alert includes MMSI, GPS position, nature of distress, and time
- ▸USCG and GMDSS stations maintain 24/7 watch on Ch 70
- ▸DSC can also be used for non-distress: vessel-to-vessel calling, position polling
- ▸After DSC alert: radio auto-switches to Ch 16 for voice
GMDSS Sea Areas
Within range of VHF DSC shore station (20–30 nm from coast)
VHF DSC + EPIRB + SART
Within range of MF DSC shore station (150–400 nm from coast)
VHF + MF DSC + Navtex + EPIRB
Within INMARSAT satellite coverage (70°N to 70°S latitude)
A1 + A2 gear + satellite EPIRB
Polar regions beyond A3 coverage (above 70° latitude)
Full GMDSS including HF DSC
GMDSS Equipment Overview
EPIRB — Emergency Position-Indicating Radio Beacon
Transmits distress signal on 406 MHz to COSPAS-SARSAT satellites; includes GPS; activates automatically when submerged. Must be registered with NOAA.
SART — Search and Rescue Transponder
Responds to X-band (9 GHz) radar — appears as a series of blips on rescuer radar. Range ~8 nm. Carried in survival craft.
PLB — Personal Locator Beacon
Personal 406 MHz distress beacon — registered to an individual. Not a substitute for EPIRB on vessels but valuable for crew members.
Navtex — Navigational Telex
Receives MSI broadcasts on 518/490 kHz automatically. Required for GMDSS A1/A2 vessels. Printed or displayed without radio operator monitoring.
GMDSS Exam Points
- ▸GMDSS required: SOLAS vessels 300 GT+, passenger vessels on international voyages
- ▸EPIRBs must be registered — unregistered EPIRBs cause unnecessary SAR responses
- ▸Category I EPIRB: auto-releases and activates when submerged 1–4 meters
- ▸Category II EPIRB: manually activated (or automatic on some models)
Automatic Identification System (AIS)
How AIS Works
- ▸Broadcasts vessel data over VHF Channels 87B and 88B
- ▸Updates every 2–10 seconds when underway; every 3 min at anchor
- ▸Transmits: MMSI, vessel name, call sign, position, COG, SOG, heading, destination
- ▸Appears on chartplotters and Vessel Traffic Service (VTS) screens
- ▸AIS does not replace radar watch or Rule of the Road compliance
- ▸Not all vessels are AIS-equipped — small boats and fishing vessels may not transmit
AIS Transponder Classes
Class A
Required on SOLAS vessels (300 GT+ international, 500 GT domestic, passenger vessels). Transmit/receive. 12.5 watts. Updates every 2–10 sec underway.
Class B
For smaller commercial and recreational vessels. Transmit/receive. 2 watts. Updates every 30 sec underway. Not required on most U.S. recreational vessels but widely used.
AIS Receiver (Receive Only)
Displays nearby AIS traffic on chartplotter without transmitting. Useful situational awareness tool; does not make the vessel visible to others.
Navtex — Maritime Safety Information
Navtex Basics
- ▸Automated telex broadcasts of Maritime Safety Information (MSI)
- ▸518 kHz: International frequency — English language broadcasts
- ▸490 kHz: National language broadcasts (non-English regions)
- ▸Range: approximately 200–400 nautical miles from transmitter
- ▸Receiver automatically prints/stores messages without operator
- ▸Required on GMDSS vessels in sea areas A1 and A2
Navtex Message Categories
Exam Tips — Marine Communications
Channel 16 is always the starting point
Every distress, urgency, or safety call starts on Channel 16. The USCG may then direct you to Channel 22A. Exam questions that ask 'where do you call first?' — the answer is Channel 16.
Channel 70 is digital only — no voice
Exam questions often test that Channel 70 is exclusively for DSC digital distress alerts. If a question says 'voice MAYDAY on Channel 70,' that is wrong. Voice MAYDAY is on Channel 16.
OVER vs. OUT
OVER means a response is expected. OUT means the conversation is done. 'Over and out' is wrong — you never use both together. This is a classic exam trap question.
Channel 13 is limited to 1 watt
Bridge-to-bridge communications on Channel 13 are required to use 1 watt maximum power. Using 25 watts on Channel 13 for routine bridge-to-bridge traffic is a violation.
MMSI must be programmed before DSC works
A DSC-capable radio without an MMSI programmed cannot send a DSC distress alert. Exam questions test whether you know that MMSI registration is a prerequisite for DSC distress function.
MAYDAY vs. PAN-PAN — know the threshold
Person actively drowning = MAYDAY. Person afloat and conscious but needs help = PAN-PAN. Engine failure in safe water = PAN-PAN. Vessel sinking = MAYDAY. The exam tests this line precisely.
Say Again — never say Repeat
On a working vessel, 'Repeat' is an artillery fire command. Marine radio procedure requires 'SAY AGAIN' to request retransmission. Exam questions may include 'Repeat' as a wrong-answer trap.
FCC Ship Station License — when required
Required for vessels traveling to foreign ports or on international voyages with passengers. Not required for domestic-only recreational vessels, but MMSI registration is still required for DSC.
Frequently Asked Questions
Which VHF channel is the international distress, safety, and calling channel?
Channel 16 (156.8 MHz) is the international distress, safety, and calling channel. All vessels equipped with a VHF radio are required to maintain a continuous watch on Channel 16 while underway, unless engaged in communications on another channel. All distress calls (MAYDAY), urgency calls (PAN-PAN), and safety calls (SECURITE) are initiated on Channel 16.
What is the difference between MAYDAY, PAN-PAN, and SECURITE?
MAYDAY (spoken three times) is used when a vessel or person is in grave and imminent danger requiring immediate assistance — fire, flooding, life-threatening injury. PAN-PAN (spoken three times) is used for urgent situations that are serious but not immediately life-threatening — a person in the water who is conscious and afloat, a medical issue, or a disabled vessel. SECURITE (spoken three times, pronounced say-CURE-ee-tay) is a safety message used to broadcast navigational or meteorological hazards — a hazard to navigation, a severe weather warning, or a floating obstruction.
What is Channel 70 used for on a VHF marine radio?
Channel 70 is exclusively reserved for Digital Selective Calling (DSC). It is a digital channel — no voice communications are permitted on Channel 70. DSC allows a vessel to send a digital distress alert that includes the vessel's MMSI number and GPS position to the Coast Guard and other DSC-equipped vessels. The USCG and all GMDSS stations maintain a continuous watch on Channel 70. After sending a DSC distress alert, the radio automatically switches to Channel 16 for voice communications.
What is Channel 22A used for?
Channel 22A is the primary working channel for communications with the U.S. Coast Guard after initial contact on Channel 16. The 'A' designation indicates the U.S. simplex frequency (157.1 MHz). After a MAYDAY or PAN-PAN call on Channel 16, the Coast Guard will typically direct the vessel to shift to Channel 22A for coordination. It is also used for broadcasts of marine safety information (MSI) by the USCG. Channel 22A is a U.S.-only designation — international vessels use Channel 22 on a different simplex frequency.
What FCC license is required to operate a VHF marine radio on a vessel?
A Ship Station License issued by the FCC (Form 605) is required for vessels that travel to foreign ports, are documented U.S. vessels over 20 meters in international waters, or carry more than six passengers for hire on international voyages. The operator of the radio must hold a Restricted Radiotelephone Operator Permit (RP) or higher. For purely domestic operation on U.S. navigable waters, a ship station license is not required for voluntarily-fitted vessels, but is still recommended. MMSI registration (through BoatUS, Sea Tow, or the FCC) is required to use the DSC distress function.
What does MMSI stand for and why is it important?
MMSI stands for Maritime Mobile Service Identity. It is a unique 9-digit number assigned to a vessel's DSC-equipped VHF radio. When a DSC distress alert is transmitted on Channel 70, the MMSI number is included in the digital signal — allowing the Coast Guard to immediately identify the vessel. For U.S. recreational vessels not required to have an FCC Ship Station License, MMSI can be obtained free through BoatUS, Sea Tow, or the USCG. The MMSI must be programmed into the radio before the DSC distress function is operational.
What prowords are used in marine radiotelephone procedure?
Standard radiotelephone prowords include: OVER — transmission complete, response expected; OUT — transmission complete, no response expected (do not say 'over and out'); ROGER — message received and understood; WILCO — will comply with instructions received; SAY AGAIN — repeat your last transmission (never use 'repeat' on a working vessel — that is an artillery fire command); BREAK — pause between parts of a message; STANDBY — wait; AFFIRMATIVE — yes; NEGATIVE — no. Clarity and brevity are required. Identify your vessel by name at the start and end of each transmission.
What is the correct MAYDAY call format?
On Channel 16, transmit: 'MAYDAY MAYDAY MAYDAY — THIS IS [vessel name × 3] — MAYDAY [vessel name] — [position: lat/lon or bearing and distance from a known landmark] — [nature of distress] — [number of persons on board] — [any other relevant information, e.g., vessel is sinking, taking on water, fire on board] — OVER.' After transmitting, listen for a response. If no response, wait 2–3 minutes and repeat. The Coast Guard monitors Channel 16 continuously. A DSC distress alert on Channel 70 should be sent simultaneously if equipment is available.
What is the phonetic alphabet used in marine communications?
The NATO phonetic alphabet is used in marine radio communications to spell out letters clearly: Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu. Numbers are spoken as: Zero, One, Two, Three, Four, Five, Six, Seven, Eight, Nine. The decimal point is spoken as 'Decimal.' Use phonetics whenever there is risk of misunderstanding a letter — vessel names, waypoints, and positions are commonly spelled out.
What is GMDSS and what vessels must comply with it?
GMDSS (Global Maritime Distress and Safety System) is an internationally agreed-upon set of safety procedures, types of equipment, and communication protocols used to increase safety and make it easier to rescue distressed ships, boats, and aircraft. Under 47 CFR Part 80, U.S. vessels on international voyages with 300 gross tons or more, and vessels that carry more than 12 passengers in the open sea, must comply with GMDSS requirements. GMDSS equipment includes DSC-capable VHF radios, EPIRBs, SARTs (Search and Rescue Transponders), and Navtex receivers. Smaller recreational and commercial vessels are not required to have full GMDSS but benefit from DSC-capable VHF radios.
What is Navtex and when is it used?
Navtex is an international automated system for distributing maritime safety information (MSI) including weather forecasts, navigational warnings, and search-and-rescue notices. It operates on 518 kHz (English, international) and 490 kHz (national language broadcasts). A Navtex receiver automatically prints or displays broadcasts without requiring a radio operator to monitor continuously. Navtex is a required component of GMDSS for vessels operating in sea areas A1 and A2. Information categories include: Navigational warnings (A), Meteorological warnings (B), Ice reports (D), Search and rescue info (G), and Weather forecasts (H).
What is AIS and what does it transmit?
AIS (Automatic Identification System) is a VHF transponder system that automatically broadcasts a vessel's identity, position, course, speed, and other data to nearby vessels and shore stations. Class A AIS transponders are required on SOLAS vessels (generally vessels over 300 GT on international voyages). Class B transponders are used by smaller commercial and recreational vessels voluntarily or by regulation. AIS transmits on VHF Channels 87B and 88B. AIS data appears on chart plotters and allows mariners to identify other vessels, receive collision alerts, and track vessel traffic. AIS does not replace radar or a visual watch.
Related Study Guides
Man Overboard Procedures
Williamson Turn, Anderson Turn, VHF Pan-Pan call, hypothermia survival times, and victim recovery.
Deck General Safety
Fire classes, PFDs, EPIRB, stability, MARPOL, and all distress equipment tested on the USCG exam.
Rules of the Road
Navigation rules, lights, sound signals, right of way, and inland/international COLREGS differences.
Practice Marine Communications Questions
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