VHF Marine Radio: The Complete Guide

Master Mariner Directory  |  2024

Every offshore sailor's communication plan begins and ends with VHF. It is the universal maritime radio standard, the legal distress channel, and the primary means of communicating with other vessels, marinas, bridges, locks, and the Coast Guard. Before you add SSB, satellite, or any other layer to your communications stack, the VHF radio needs to be working correctly, you need to understand how to use it, and your MMSI number needs to be registered and programmed into the DSC controller.

VHF marine radio operates on frequencies between 156 and 174 MHz using FM modulation. Unlike HF/SSB radio, VHF propagation is essentially line-of-sight — signals do not bounce off the ionosphere. This limits range significantly, but it also means VHF communications are local and clear, without the fading and interference that characterizes shortwave. Within its range, a VHF radio is more reliable than any other marine communication system.

Channel 16: The International Distress and Calling Channel

Channel 16 (156.800 MHz) is the international distress, safety, and calling channel for VHF marine radio. Under USCG regulations and international maritime law, all vessels equipped with VHF radios are required to maintain a watch on Channel 16 whenever the radio is on and the vessel is underway. This is not optional, and it is not an informal convention — it is the law, and it is the foundation of the maritime rescue system.

In practice, Channel 16 is used for two purposes: initial contact (you hail another vessel, marina, or the Coast Guard on 16, then immediately switch to a working channel) and distress (mayday calls go out on 16 and the responding party coordinates on 16 before switching if necessary). You should never have a long conversation on Channel 16. Hail, make contact, announce the working channel, and move.

The Coast Guard monitors Channel 16 continuously from its sector stations and through a network of remote receivers. USCG response time to a properly transmitted mayday on Channel 16 is typically minutes, not hours, in US coastal waters.

DSC: Digital Selective Calling and MMSI Registration

Digital Selective Calling is the digital signaling layer built into modern Class D (fixed-mount) and many Class B (handheld) VHF radios. The essential thing to understand about DSC: when you press the red distress button on a DSC-equipped VHF radio, the radio transmits a digital distress signal on Channel 70 (the dedicated DSC channel) that includes your MMSI number, the nature of the distress, and — if connected to a GPS — your exact position. All of this happens automatically and simultaneously, before any voice call.

The MMSI (Maritime Mobile Service Identity) is a nine-digit number unique to your vessel. Without a registered MMSI, your DSC distress call still goes out, but the Coast Guard cannot immediately identify who is calling or match the signal to a vessel record. With a registered MMSI, the USCG Rescue Coordination Center pulls up your vessel name, description, hailing port, registered owner, and emergency contacts within seconds of receiving the signal.

US recreational boaters can register an MMSI for free through BoatUS (boatus.com/mmsi) or Sea Tow. FCC registration is required if the vessel travels outside US waters. Programming the MMSI into your DSC radio is a one-time setup task — consult your radio's manual, as the procedure varies by manufacturer. The GPS connection is critical: run the NMEA cable from your chartplotter to the VHF radio so that position is automatically included in any DSC transmission.

Channel Assignments

VHF marine channels in the US are assigned specific uses by the FCC. The most important for recreational sailors:

• Channel 16: International distress, safety, and calling. Monitor at all times.
• Channel 22A: USCG working channel. After initial contact on 16, the Coast Guard will direct you to 22A for further communication.
• Channel 09: Alternate recreational hailing channel used by marinas and some recreational boaters when 16 traffic is heavy.
• Channels 68, 69, 71, 72: Non-commercial recreational working channels. Used for vessel-to-vessel communication after hailing on 16.
• Channel 13: Bridge-to-bridge navigation. Used for communicating with commercial vessels and for bridge tenders. Low power (1 watt) only.
• Channel 70: DSC digital calling only. Never use for voice.
• WX1–WX7: NOAA Weather Radio broadcasts (see below).

Note that "Channel 22A" is the US version of Channel 22 — the "A" designation indicates the slightly different frequency used in the US compared to the international standard. Most modern marine VHF radios handle this automatically.

VHF Range: The Antenna Height Reality

VHF propagation is line-of-sight. The formula that matters: the radio horizon in nautical miles is approximately 1.23 times the square root of the antenna height in feet. A masthead antenna at 50 feet gives a radio horizon of about 8.7 nautical miles. A handheld held at cockpit level (4 feet) has a horizon of about 2.5nm.

In practice, boat-to-boat communication between two vessels with masthead antennas typically reaches 10–15nm. From a vessel to a USCG shore station with a tower-mounted antenna at 200 feet or more, range extends to 20–25nm or beyond. The figure most often cited — 5–7nm for boat-to-boat — applies to vessels without masthead antennas or with handheld radios.

Antenna gain is a secondary factor. A standard masthead marine antenna is 6 dBi. Higher-gain antennas (9 dBi) compress the radiation pattern horizontally, which increases horizontal range in calm conditions but can reduce effective gain when the vessel is heeled. For offshore work, 6 dBi at the masthead is the standard recommendation — more gain, in practice, rarely delivers the range improvement the spec sheet suggests.

Class D Fixed Mount vs. Class B Handheld

Every offshore vessel should carry both: a fixed-mount Class D VHF (25-watt maximum, connected to a masthead antenna and to GPS for DSC) and at least one waterproof Class B handheld (5–6 watts). The fixed mount is your primary communications station while aboard. The handheld is for two specific situations: vessel-to-vessel communication when deck work keeps you away from the chart table, and — most critically — as the communications device you take when abandoning ship.

If you ever have to leave the boat in an emergency, you take the EPIRB and you take the handheld VHF. The EPIRB gets the satellites' attention; the VHF lets the rescue helicopter talk to you directly as it approaches. A handheld VHF that floats and has a charged battery is not optional safety equipment offshore.

NOAA Weather Radio

NOAA broadcasts continuous weather forecasts and marine weather for US coastal and offshore waters on seven VHF frequencies, WX1 through WX7 (162.400 to 162.550 MHz). The broadcasts are updated every few hours and include zone forecasts, offshore forecasts, and — during severe weather — special marine warnings. All modern VHF marine radios include a dedicated weather band button. Learn your local WX channel (WX1 covers much of the Northeast, WX2 the Southeast, and so on — check NOAA's regional station list for your area).

Many fixed-mount VHF radios include a weather alert feature that triggers an alarm when NOAA broadcasts a hazardous weather notification. Enable this feature before any passage. It has woken up more than a few offshore sailors to a squall line developing faster than expected.

Making a Proper Distress, Urgency, or Safety Call

Maritime radio procedure distinguishes three levels of calls, each with a specific prefix and protocol:

MAYDAY — immediate danger to life or vessel. Transmitted on Channel 16 at full power. The scripted procedure: "MAYDAY MAYDAY MAYDAY — This is [vessel name, repeated three times] — MAYDAY — [vessel name] — My position is [lat/lon or bearing and distance from a known point] — [nature of distress] — [number of persons aboard] — [any other relevant information] — MAYDAY — [vessel name] — Over." Repeat until answered.

PAN-PAN (pronounced "pahn-pahn") — urgent situation, not immediately life-threatening. Medical emergencies where the patient is stable but requires attention; vessel taking on water but still afloat; person in the water already recovered but needing medical evacuation. Same Channel 16 procedure, substitute "PAN-PAN PAN-PAN PAN-PAN" for MAYDAY.

SECURITÉ (pronounced "say-cure-ee-tay") — safety call to warn other mariners of a navigation hazard. Debris in the water, a vessel adrift without crew, a hazard to navigation. Transmitted on Channel 16 for coast stations, or Channel 13 for vessel traffic.

Practice these calls out loud before you need them. The scripted procedure exists because people under stress forget things, and a complete, properly transmitted mayday call provides the Coast Guard everything it needs to dispatch rescue resources immediately.

VHF Licensing Requirements

In the United States, no radio operator's license is required to operate a marine VHF radio in domestic waters. You can purchase a radio, install it, and use it without any license as long as you remain in US waters. However, if your vessel leaves US jurisdiction — including into Canadian or Mexican waters, or offshore beyond the 12nm territorial sea — two licenses are required: an FCC Ship Station License (for the radio installation) and an FCC Restricted Radiotelephone Operator Permit (for the operator). Both can be obtained online from the FCC; the Ship Station License is vessel-based, the Operator Permit is person-based and required for anyone who might operate the radio internationally.

The FCC Restricted Radiotelephone Operator Permit is also required if you make international phone patch calls via marine operator (now largely obsolete) or operate on frequencies outside the normal recreational VHF band. For the vast majority of coastal and nearshore sailors who never leave US waters, no license of any kind is legally required, though carrying documentation of MMSI registration is good practice.

← All Communications Guides  |  SSB Radio Offshore →

Frequently Asked Questions

What is Channel 16 and why must it always be monitored? Channel 16 (156.800 MHz) is the international maritime distress, safety, and calling frequency. By law in most jurisdictions, all vessels equipped with VHF radios must monitor Channel 16 whenever the radio is on. It is the channel on which distress calls (MAYDAY) are transmitted, on which the US Coast Guard broadcasts safety notices, and on which vessels hail each other before switching to a working channel.

What is a MMSI number and how does DSC work? A Maritime Mobile Service Identity (MMSI) is a unique nine-digit number permanently assigned to a vessel's VHF radio, functioning as the radio equivalent of a phone number. Digital Selective Calling (DSC) uses the MMSI to transmit a distress alert automatically — including GPS position if the radio is connected to a GPS feed — when the dedicated red distress button is held. Coast Guard and nearby vessels with DSC-enabled radios receive the alert immediately with vessel identification and position.

How is VHF radio range calculated and what limits it offshore? VHF radio range is calculated using the formula 1.23 × √height(ft) nautical miles, where height is the antenna height above sea level. A masthead antenna at 50 feet has a theoretical range of approximately 8.7 nautical miles to a vessel at sea level. Range is limited by the curvature of the earth (line-of-sight propagation), which is why coast guard stations mounted at height can communicate over much longer distances than vessel-to-vessel contacts between masthead antennas.

What is Channel 22A and when should it be used? Channel 22A is the designated working channel for communications with US Coast Guard stations. After initial contact on Channel 16, the Coast Guard will typically ask vessels to switch to Channel 22A for extended communications, weather reports, or broadcasts. This frees Channel 16 for emergency traffic while maintaining the USCG communication. The 'A' designation indicates the US-specific variant of the channel frequency.

What FCC licence is required to operate a marine VHF radio and when is it needed? In US waters, recreational boaters are not required to hold a licence to operate a VHF radio on domestic voyages. However, any vessel that travels to foreign ports or operates on international waters must have a ship station licence from the FCC, and the operator must hold a Restricted Radiotelephone Operator Permit. The permit requires passing a basic examination on radio procedure and regulations.