DSC (Digital Selective Calling) — the part of a VHF marine radio that can automatically transmit who you are.
📡 MMSI + DSC (Digital Selective Calling)
A DSC-equipped VHF marine radio can broadcast your registered identity — your MMSI number (Maritime Mobile Service Identity).
When you press the DISTRESS button (the red SOS button with a cover), the radio automatically sends a digital coded message that includes:
- Your MMSI (your vessel’s ID)
- Your GPS coordinates (if the VHF is connected to your chartplotter/GPS – which your Simrad can do)
- Nature of distress, if programmed
- Continuous automated distress alerts until acknowledged
This allows the Coast Guard and nearby vessels to instantly know who is calling and where you are, without you having to say anything.
📌 How it works
When you hit the DSC distress button:
- The radio sends a digital burst on Channel 70.
- All DSC radios in range receive it.
- Your identity (MMSI) and position are automatically transmitted.
🧭 Other DSC Functions
Besides distress, DSC can also:
✔ Make individual calls to another boat using their MMSI
(Like calling a phone number — their radio rings)
✔ Make group calls
✔ Send position requests and position reports
What is an MMSI number, and why do you need one?
An MMSI number is basically a phone number for your boat. When your VHF radio has Digital Selective Calling (DSC), you can press one emergency button and your radio automatically sends out your identity and location to every other DSC-equipped boat nearby — including the Coast Guard.
If your VHF radio was made after 1999, it almost certainly has DSC built in.
But to use those safety features, your radio needs an MMSI number programmed into it.
In short:
Your MMSI makes your emergency call faster, more accurate, and automatically sends out who you are and where you are — all with one button.
When your VHF radio is connected to your GPS, pressing the DSC distress button sends out your exact location and the type of emergency. Other boats with chartplotters will actually see your position pop up as an icon on their screens. Their systems can then calculate how far away you are and the direction to reach you — which means nearby boaters may be able to help quicker than the Coast Guard (but always follow Coast Guard instructions during any emergency).
An MMSI number also lets you “call” other boats directly using DSC, which reduces unnecessary chatter on busy channels like 16.
The U.S. Coast Guard can use your MMSI information for faster search and rescue inside areas covered by the Rescue 21 system.
Important:
If you plan to travel outside U.S. waters, you must get your MMSI through the FCC so it’s recognized internationally.
Updating or Registering Your MMSI is Easy
If you already have an MMSI number and just need to update your information, you can do that using the link below.
If you’re registering for a new MMSI, you’ll need to go through the United States Power Squadrons (America’s Boating Club), since Sea Tow no longer issues MMSI numbers.
Note:
Federal agencies get their MMSI numbers through their internal spectrum management offices.
Official DHS and U.S. Coast Guard vessels receive MMSI assignments through Commandant (CG-652).
U.S. Coast Guard Auxiliary operators should request their MMSI the same way as any other non-federal U.S. boater.
https://www.usps.org/php/mmsi_new/index.php
Modern marine radios now come with Digital Selective Calling (DSC), which lets you make routine calls and send automatic distress alerts at the push of a button.
To use these features, your radio needs a unique ID called an MMSI (Maritime Mobile Service Identity).
The United States Power Squadrons (America’s Boating Club) is authorized by both the FCC and the U.S. Coast Guard to issue MMSI numbers for most U.S. recreational boats — basically any vessel not required to meet the SOLAS (Safety of Life at Sea) rules.
If your boat needs an FCC ship station license (for example, if you’re a U.S. pleasure craft traveling internationally), then you must get your MMSI directly from the FCC instead.
Click here to see if you qualify for this MMSI program.
This website will guide you through getting an MMSI for your boat free of charge.
Once issued, your MMSI is unique to your vessel and should be programmed into every piece of equipment you have that can send or receive digital DSC signals (such as your VHF radio and AIS).
📡 VHF Marine Radio Channels — Quick Reference
Essential Hailing & Distress
- Channel 16 — Distress, Safety, and Calling (Primary)
- Used to hail other vessels and for all emergency calls.
- Channel 9 — Secondary Calling Channel
- Recreational hailing when allowed, reduces congestion on 16.
- Channel 70 — Digital Selective Calling (DSC) Only
- No voice. Used by DSC radios for automated distress, position, and hailing signals.
Ship-to-Ship & Working Channels
- 6 — Ship-to-ship safety & SAR communications
- 13 — Bridge-to-bridge navigation (commercial traffic; low power)
- 67 — Bridge-to-bridge / ship-to-ship (may vary by region)
- 20, 68, 69, 71 — Common working channels for recreational vessel-to-vessel communication
Coast Guard Channels
- 22A — USCG Marine Information & Safety Broadcasts
- Used after the Coast Guard contacts you on Channel 16 and directs you to switch to 22A.
Weather
- WX1 – WX10 (or WX11–WX14 depending on radio)
- Continuous NOAA weather broadcasts
- Some radios automatically scan for strongest WX signal.
🚨 Priority Radio Calls (Severity Levels)
- SECURITÉ (pronounced seh-cure-ih-tay)
⚠️ Safety message
Used for navigational warnings (e.g., hazards, weather updates, fog). - PAN-PAN
⚠️ Urgent situation
Not life-threatening, but requires attention (e.g., engine failure, taking on water slowly). - MAYDAY
🚨 Grave and imminent danger
Life-threatening emergencies only (e.g., sinking, fire, medical emergency, man overboard).
🔤 NATO Phonetic Alphabet
| Letter | Code Word | Pronunciation |
|---|---|---|
| A | Alpha | AL-fah |
| B | Bravo | BRAH-voh |
| C | Charlie | CHAR-lee |
| D | Delta | DELL-tah |
| E | Echo | ECK-oh |
| F | Foxtrot | FOKS-trot |
| G | Golf | GOLF |
| H | Hotel | ho-TELL |
| I | India | IN-dee-ah |
| J | Juliett | JEW-lee-ETT |
| K | Kilo | KEY-loh |
| L | Lima | LEE-mah |
| M | Mike | MIKE |
| N | November | no-VEM-ber |
| O | Oscar | OSS-car |
| P | Papa | pah-PAH |
| Q | Quebec | keh-BECK |
| R | Romeo | ROW-me-oh |
| S | Sierra | see-AIR-ah |
| T | Tango | TANG-go |
| U | Uniform | YOU-nih-form |
| V | Victor | VIK-ter |
| W | Whiskey | WISS-key |
| X | X-ray | EKS-ray |
| Y | Yankee | YANG-kee |
| Z | Zulu | ZOO-loo |