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Why A VHF Radio Is Best For An Emergency

Being able to communicate with other boaters and rescue agencies makes having a VHF a necessity no matter how small your boat.

VHF radio in use

Photo: Billy Black

Your VHF radio should be your go-to communications in an emergency. The U.S. Coast Guard has a huge network of towers to listen in on distress calls and when you make a call, every other nearby boater with a radio on can also hear you, which increases your chance of getting help. Knowing a little about your VHF and how to make the call can help when you really need it.

Fixed-Mount VHF Radios

Arguably one of the most cost-effective safety items you can have on any boat, a fixed-mount VHF allows you to communicate with a wide range of people and organizations: the U.S. Coast Guard, commercial ships, the Rescue 21 network, bridge tenders, TowBoatUS, race committees, and countless others stations. And its full potential is realized when units with Digital Selective Calling, or DSC, are connected to an operational GPS receiver (or have one internally). While all radios sold in the U.S. over the last decade are equipped with DSC, many operators (the U.S. Coast Guard says about 85 percent) either have not connected their radios to their GPS, nor registered for an MMSI (Marine Mobile Service Identity) number. This is vital for the full functionality of the Rescue 21 system.

Fixed-mount VHF radios are only as good as their antenna systems (a combination of the antenna, coaxial cable, and connections). Antennas should be mounted as high as possible: on the masthead of a sailboat or on the flybridge of a powerboat. Because VHF signals travel more or less in a straight line, a higher antenna will allow a VHF signal to reach more distant stations due to the Earth's curvature.

The Invaluable Phonetic Alphabet

To make sure you're clearly understood, especially when using the VHF radio, words often need to be spelled out using what's known as the phonetic alphabet. On a radio transmission, static can produce mistakes. For instance, over the past couple of years, a popular boat name, according to our BoatUS records, has been Blew By You. In audio communications, this can be mistaken for Blue Bayou. Learn the phonetic alphabet by heart so that you can easily spell out names and words quickly, especially in emergency situations. BoatUS spelled out is Bravo Oscar Alpha Tango Uniform Sierra.

A: Alpha G: Golf M: Mike S: Sierra Y: Yankee
B: Bravo H: Hotel N: November T: Tango Z: Zulu
C: Charlie I: India O: Oscar U: Uniform  
D: Delta J: Juliet P: Papa V: Victor  
E: Echo K: Kilo Q: Quebec W: Whiskey  
F: Foxtrot L: Lima R: Romeo X: X-ray  

Handheld VHF Radios

This small, portable transceiver provides short-range voice communications of up to 5 miles to other vessels and up to 20 miles to land-based stations (see the section "Digital Selective Calling and Rescue 21"). They're frequently waterproof, and many models float if dropped in the water. Rechargeable batteries last for 8 to 15 hours, assuming usage roughly correlates to the 90-5-5 rule: The radio is in standby mode 90 percent of the time, used for transmitting 5 percent of the time, and used for receiving 5 percent of the time. Handheld VHF radios like other portable electronics have several advantages over fixed-mount radios, especially during emergencies:

  • Internal batteries are independent of the vessel's electrical system.
  • Self-contained antennas work even if the vessel's antenna is not in place or is damaged.
  • They can be used anywhere on board.

Their primary disadvantage is range. Since VHF transmissions work on line of sight, a handheld will have significantly shorter range than a properly installed fixed-mount VHF.

The addition of GPS and DSC is a big improvement to handheld VHFs. Users can "press the red button" to summon help from other vessels or the U.S. Coast Guard's Rescue 21 network (see the section below "How To Make A MayDay Call On A VHF"). This creates a very inexpensive personal communications solution that covers both voice and emergency digital communications within about 20 miles of the U.S. coast, or anywhere in the Great Lakes.

Cellphone Vs. VHF

Cellular phones are inferior to handheld VHF radios in many respects. They're often not waterproof, you can't communicate with more than one person at a time, and you have to know that person's number. However, having a cellular telephone onboard does make it possible to call any phone number when close to shore (including Rescue Coordination Centers). And texting can also be useful, especially if you are on the edge of cellular coverage.

Digital Selective Calling And Rescue 21

DSC uses VHF Channel 70 as a digital-only channel. Since March 2011, all fixed-mount radios sold in the U.S. have DSC capability built in. They must be connected to an operating GPS for full capability (or have an internal GPS receiver) and require the MMSI number registered to your vessel to be entered into the radio. DSC-capable radios can be used to send various types of messages:

  • Calls to specific vessels, requesting a voice response
  • Calls to specific vessels, requesting their position
  • Calls to specific vessels, providing position
  • Calls to groups of vessels
  • Emergency calls to the Coast Guard and other vessels.

Calls to specific vessels, or to groups of vessels, require you to know the MMSI of that vessel or the group MMSI. Emergency calls is the category of greatest interest to coastal and offshore boaters. When an MMSI number has been entered into a VHF radio, and when it is connected to an operating GPS, DSC allows you to broadcast a mayday transmission to all vessels within range and, if you're within 20 to 40 nautical miles of shore, your transmission will be picked up by the Coast Guard's Rescue 21 network of shore stations. This distress call communicates your identification and your position in one brief call.

Coax Max Length
Type Diameter (mm) Meters Feet
RG-58 5 11.75 38.5
RG-8X 6.1 14.5 47.5
LMR-lw200 5 16.6 54.5
LMR-lw249 6.1 22.2 72.8
RG-8/U 10.3 27.1 88.9

Rescue 21 comprises a series of VHF antennas located on high towers or mountains along the coast of the continental U.S., the Great Lakes, Hawaii, several Trust Territories, and in portions of Alaska. These antennas are connected to a network of communication stations associated with the Coast Guard sectors, which make up the Coast Guard's VHF distress system. Rescue 21 gives Coast Guard radio watch standers several advantages:

  • Coverage out to 20 nautical miles offshore (minimum) for communication to a 1-watt transmitter located 2 meters above the water
  • Transmissions are recorded for later playback and review
  • Direction finding (DF) and/or triangulation helps locate a radio transmission (whether or not it includes a digital position in the transmission)
  • Full DSC capabilities, including monitoring VHF Channel 70 and receiving digital messages including position.

Rescue 21 is now implemented across the country, and it's the single best reason to ensure you have a DSC radio correctly installed. Sailors who venture offshore without an MMSI number, a properly connected GPS, and a quality antenna installation will not be able to take full advantage of the over $1 billion dollar maritime safety net that Rescue 21 provides.

How To Call for a Boat Tow

Emergency Procedure Words

There are three emergency procedure words that carry extra importance when you're communicating by radio. In order of decreasing severity, they are mayday, pan-pan, and sécurité.

Through the use of these words, you will alert all mariners to the seriousness of your transmission, and to the possibility that they might be involved in lending assistance. All three are anglicized versions of French words, and each is repeated three times in succession so that those who hear the transmission understand that they're hearing an actual call for help and not a discussion of another vessel's distress call. (See additional comments on mayday relay below.)

Word Derivation Meaning When To Use Comment
MAYDAY From the French "m'aidez," which means "help me" A vessel and/or crew is in grave and imminent danger Life-threatening medical emergency; possibility of losing the boat Use for imminent danger only
PAN-PAN From the French "panne," which means "broken" A vessel requires urgent assistance Serious mechanical breakdown; urgent but not life-threatening medical issues Because it handles such a wide range of difficulties, details can be added to the transmission: "Pan-pan, pan-pan, pan-pan, this is the vessel Surprise requesting medical advice, over."
SÉCURITÉ French for "safety" Important safety information follows Information that could be important to another vessel's safety Covers a wide range of issues: hazards to navigation, pyrotechnic demonstrations, Coast Guard Marine Safety Broadcasts, large vessel traffic alerts"
When you hear a transmission that uses one of the three emergency words, what action should you take? A lot depends on your proximity to the vessel or incident in question. It also depends on your ability to respond and give assistance. If you hear a mayday and you are the most appropriate vessel to respond, you are legally and morally required to lend assistance, if you can do so without endangering your crew or vessel.

Common VHF Channels And Their Uses

While VHF radios may have anywhere from 55 to 80 channels, there are relatively few that can be used by recreational boaters. This table lists the most common ones, but because VHF channel use is somewhat geographically specific, a few channels may be different in your home waters. The VHF channels used in Canada and Internationally may have different frequencies and different functions than those used in the U.S.

Channel Simplex/Duplex* Purpose
*A simplex channel transmits and receives on the same frequency. Duplex channels use different frequencies for transmitting and receiving.
16 Simplex International distress, safety, and hailing. Monitoring required while underway.
6 Simplex Intership safety. Frequently used by towing companies.
22A Simplex U.S. Coast Guard working channel. Referred to as "22 Alpha." Maritime Safety Information Broadcasts are announced on Channel 16, then broadcast on 22A.
21A, 23A Simplex U.S. Coast Guard only. In rare instances, the Coast Guard may ask you to communicate with them on these channels.
9 Simplex Boater calling (commercial and noncommercial). Recommended for hailing another vessel (to reduce traffic on Channel 16). Many radios can monitor 16, 9, and a working channel.
13 Simplex Intership navigation safety. Ships are required to monitor Channel 13 when at sea. Effective if you are trying to contact a specific vessel in your area, especially if there is risk of collision. Transmissions are limited to 1W to reduce interference.
14 Simplex Port operations. In areas with Vessel Traffic Service (VTS), this is the channel they use to communicate with large ship traffic. Can be very helpful for tracking vessels.
24-28, 84-87 Duplex Port operations. In areas with Vessel Traffic Service (VTS), this is the channel they use to communicate with large ship traffic. Can be very helpful for tracking vessels.
68, 69, 71, 78A Simplex For noncommercial communications with other vessels or shore stations. Traffic must be concise. Commonly used by race committees, along with Channel 72.
72 Simplex Similar to previous channels but only for ship-to-ship. No land-based stations can use channel 72.
70 Simplex Digital only; used by DSC functions on the radio.
WX 1-9 Simplex NOAA weather channels. Local weather is usually on WX1-WX4.

Mayday Relay

If you're the only person to hear a mayday call from another vessel, you may have to act as a relay to rebroadcast vital information to the Coast Guard or other rescue agencies. In that case, use the words "mayday relay." This tells other vessels and stations that you're not the one in trouble, but aware of a vessel in trouble.

Finally, nothing is more frustrating than hearing a mayday call, then having another vessel break in with low-priority traffic. If this happens, the vessel in distress can remind them to keep the channel open (assuming they've taken a Safety at Sea seminar or have read Chapman Piloting & Seamanship) by saying Silence Mayday (pronounced "seelonce mayday"). At the end of the emergency, the transmission Silence Fini (pronounced "seelonce feenee") tells other mariners that normal communications can resume. The French pronunciation helps differentiate these words from the normal stream of radio traffic, but it's certainly no time to worry about perfecting your accent.

How To Use Your VHF Radio to Call for Help in a Boat Emergency

How To Make A Mayday Call On A VHF

When you need help, every second counts. The goal is to broadcast the most important information as quickly and clearly as possible.

If you have a DSC-equipped radio, flip up the cover on the DSC button and press the button for 3 to 5 seconds. Some radios will allow you to choose your problem from a list (Fire/Explosion, Flooding, Collision, Grounding, Capsizing, Sinking, Adrift, Abandoning Ship, Piracy, Man Overboard) so that vessels receiving your transmission will automatically know what happened. After the radio transmits your position, MMSI number, and the nature of your distress, it will revert to Channel 16 so you can make a voice transmission.

Icom IC M422 VHF marine radio

The regulations require a two-step process to send a DSC distress call, so most radios will have a spring-loaded red cover over a red button. Press and hold for 5 seconds.

If you don't have a DSC-equipped radio, select Channel 16 and high power (25W), press the transmit button, and say the following:

"Mayday!, Mayday!, Mayday!" (Urgency word three times.)

"This is the vessel Surprise, Surprise, Surprise." (Vessel name three times.)

"Mayday Surprise."

"We are located at ..." [insert latitude and longitude of your location]

"Surprise is a 38-foot yawl with a blue hull and a tan deck." [Description of vessel.]

"We are taking on water, and we cannot find the leak. We request immediate assistance." [Nature of the emergency.]

"There are six crew on board. We have a life raft, EPIRB, and life jackets." [Number of crew and information on safety equipment.]

"This is the vessel Surprise standing by on Channel 16." [Complete the call and let potential responders know that you are standing by.]

Excerpted from US Sailing's Safety at Sea: A Guide to Safety Under Sail and Personal Survival, available for purchase.

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Chuck Hawley

Contributor, BoatUS Magazine

Chuck Hawley is the chairman of the US Sailing Safety at Sea Committee. A lifelong sailor, he has made two singlehanded passages to Hawaii, three crewed trans-Pacific races, and a World Record attempt on the west-to-east trans-Atlantic record. He is a nationally known speaker on marine safety and one of five moderators of the US Sailing Safety at Sea Seminars. He’s also a Powerboat Instructor for US Sailing. Chuck has worked for West Marine for nearly three decades and is responsible for the product content on He lives in Santa Cruz, Calif., with his wife, Susan, and five daughters.