Do-It-Yourself: Making a Mayday Call on Your VHF Radio


red coast guard helicopter

By Tom Burden, Last updated: 4/15/2019

A Mayday call indicates that life and property are at acute risk. We hope you never have to refer to this West Advisor while at sea because it means that your boat or someone on it is in imminent danger. A Mayday call is warranted in cases of serious damage, danger of losing the vessel and life-threatening injury or illness of someone aboard. A distress call on Channel 16 should follow a certain protocol to make sure it is clearly understood and contains the necessary information that will guide rescuers to you as quickly as possible. We’ll run through the protocols below. First, you should understand why your VHF radio is critically important in a boating emergency.

A Mobile Phone is No Substitute for VHF

Your smartphone is not a substitute for a marine VHF radio. Cell phones lose service when you're more than a  few miles from shore and your phone can only communicate with one number at a time. Even if you know and call the local Coast Guard phone number they have no way of knowing where you are unless you tell them and if your call is dropped they may be unable to call you back. VHF radios broadcast your distress call, including location and identification, to the Coast Guard as well as any other boats within radio range which can be up to 20 nautical miles. Don't risk the life of yourself or others. A VHF radio is a necessary safety device on any boat.

Advantages of DSC Distress Calling

Digital selective calling (DSC) distress calls are sent automatically with the push of a button. They tell the Coast Guard who you are (the name of your boat) and where you are (Lat. and Long).  Your digital signal can be received and accurately decoded under conditions where voice messages are difficult to understand. Your message is automatically stored and displayed on every DSC radio that receives it and the Coast Guard’s response automatically switches your radio to Channel 16 for voice communication.

Coast Guard units monitor DSC distress calls meaning all Coast Guard vessels in radio range of your boat are alerted immediately. Since your radio transmits your precise location, the Search phase of Search and Rescue is greatly reduced. The help you need arrives sooner, and Coast Guard crews spend less time exposed to hazardous weather conditions.

NOTE: Your VHF radio (and everyone else’s) MUST be on and tuned to Channel 16 whenever the boat is in motion unless you’re communicating on another channel. This may save your life or someone else’s.

fire extinguisher, first aid kit and life jacket on a boat

A proper DSC setup for your radio is as important for safety as other gear such as fire extinguishers, first aid kits and life vests.

Equipping Your Boat for DSC

Using DSC to send a distress call can save your life and setup is simple. Only five items are needed:

  • 1. Your unique Maritime Mobile Service Identity Number (MMSI)
  • 2. VHF/DSC radio
  • 3. GPS receiver
  • 4. Two-wire connection between VHF and GPS
  • 5. A few minutes to learn the DSC system

To obtain and register your MMSI number, the Coast Guard recommends visiting the website boatus.com/mmsi and following the instructions. The registration is free for BoatUS Members and costs $25 for non-members. Once you have your MMSI number, enter it into your radio’s memory, and connect your VHF radio to a GPS receiver. Your GPS receiver must be turned on while you are underway or your radio will not be able to send your position in a distress call.

Unfortunately, boaters are not following these simple steps for installing this important safety gear. According to the U.S. Coast Guard, "approximately 90 percent of VHF DSC distress alerts received by the Coast Guard do not contain position information, and approximately 60 percent do not contain a registered identity."

Without location or indentification information included in a distress call, the coast guard can do little to help and the potential life saving aspects of DSC technology is lost. Boaters, this is a serious problem. Please provide the information the Coast Guard needs to rescue you in an emergency!

sailboat with a man overboard

Making a Distress Call

Here are the steps to set off a distress call that will get the job done:

  • Locate the DISTRESS button.
  • Lift the cover.
  • Press and hold the button until the radio “beeps”. The DSC signal will tell the Coast Guard your boat’s information.
  • Select the nature of your call (if your radio allows you to make this selection).
  • Say loud and clearly “Mayday, Mayday, Mayday. This is vessel (use your boat’s name).”
  • Repeat three times. If you use a handheld, make sure you set the transmission power to 5 or 6 Watts (the highest power setting on your particular handheld).
  • Repeat Mayday and your boat’s name once again.
  • Provide your exact position (how good it is to have a GPS) in degrees of latitude and longitude. If you don’t know your lat/long coordinates you should provide a magnetic bearing or an estimated distance and direction to an easily identified landmark or aid to navigation.
  • Describe your boat. Give type (power, sail), design (cabin cruiser, sloop), length, color and other distinctive features.
  • Say how many people are on board.
  • Give concise information about the nature of your distress. Are you sinking? Is someone injured? Do you have fire on board? Has crew fallen over board? What kind of equipment do you need to control the situation (medical advice or support, fire extinguisher, pumps etc.)?
  • If your boat is in danger of sinking, indicate how much time you think you have left.
  • At the end of the transmission say “Over” and listen for a response. Let a minute go by before you repeat the entire process.

When the Coast Guard receives your DSC distress call, the watchstander on duty is alerted, the Coast Guard’s DSC signals your radio to switch to Channel 16, your radio announces receipt of the Coast Guard’s signal, and the Coast Guard establishes voice communication with you.

When your MAYDAY call is answered, respond with the name of your boat, the latitude/longitude numbers from your GPS, and why you need help.

  • This is (name of your boat)
  • My position is (your latitude and longitude)
  • We are (state the nature of your problem—sinking, flooding, fire, medical emergency etc.)
  • We have (number of people) onboard, over
boaters on a liferaft signaling for help

What to Do If You Hear a MAYDAY Call

All DSC radios receiving a distress call immediately sound a distinctive alarm, and automatically switch to Channel 16 for voice communication.

  • Your radio will “beep” upon receipt of a DSC distress call
  • The radio will automatically switch to Channel 16, and display the calling station’s MMSI, latitude, longitude and time of call
  • Write down the message, the name of the boat in distress, its position and the reason for the call. Don’t trust your memory. Record it on paper.
  • If the Coast Guard does not answer within two minutes, call them on Channel 16 and repeat the distress message, stating clearly that you are relaying the message
  • Stand by on Channel 16 and follow the instructions of the Coast Guard
  • Do not make routine calls on Channel 16
  • Prepare to assist the vessel in distress (if possible)

If You Make an Accidental Distress Call

  • Don’t panic
  • Turn the radio off and turn it back on. This will stop the broadcasting of the distress signal.
  • Select Channel 16 and make a voice broadcast explaining that you have made an accidental distress call.
  • Continue to monitor Channel 16

Making a DSC Test Call

  • DO NOT use the Distress button
  • Determine a friend’s MMSI or that of a shore station
  • Enter the MMSI that you wish to call in your radio
  • Choose a working channel (NOT Channel 16)
  • Select “Routine Call” from the list of DSC calls available on your radio.
  • Press the “Enter” button

Your radio will indicate that the call has been sent, indicate that the station you called has received your call and switch to the working channel you had selected before you made the DSC call. The station you called will switch to the working channel you chose. You can communicate with the station you called to confirm that everything is working properly.

Other Calls

Pan Pan (Pahn Pahn)

  • Urgency signal “Pan Pan” repeated three times
  • Announces an urgent message, a request for assistance if a boat or its crew is in danger, but the situation is not life-threatening
  • Used to gain attention of other vessels

Securité (Say-cure-it-tay)

  • Safety signal message “Securité” repeated three times
  • Announces important information, such as a warning to other shipping
  • Examples: Dangerous debris in the water; Intention of large vessel to get under way

All Ships

  • Contact nearby but unknown vessel
  • Most appropriate for use on the high seas
  • Causes all receiving DSC radios to automatically return to Channel 16
  • Do not use in port or harbor unless necessary

What You Need to Know About Your VHF/DSC Radio

This online presentation developed by the US Coast Guard and the BoatU.S. Foundation is simply the best summary of VHF and DSC radios we have ever seen: How they work, Rescue 21, distress calls, three types of DSC, Pan Pan/Securite/All Ships, etc. It includes a VHF/DSC radio simulator that even has a working squelch control.

Spend 37 minutes and 25 seconds watching this online tutorial, and you will become a safer and more knowledgeable VHF radio operator. Can You Hear Me?