VHF radio is not optional even if you carry a satellite phone, even if you have an EPIRB, even if you have a handheld PLB. Every vessel you might encounter in an emergency — the Coast Guard, a towing service, a passing ship, the harbor master at your destination — can hear you on VHF. A satellite phone call goes to a call center. A VHF distress call goes directly to everyone within 20 miles.

Most recreational sailors understand this in principle but don't use their radio correctly. The DSC function that makes modern VHF radios dramatically more effective is configured on roughly 30% of boats that carry it. This is a solvable problem.

Channel 16: The Monitoring Requirement

Channel 16 (156.800 MHz) is the international distress and calling frequency. The FCC requires all vessels equipped with VHF to monitor Channel 16 when underway. The practical reason is simple: if someone calls a Mayday in your area, Channel 16 is where you'll hear it. Coast Guard broadcasts — weather warnings, safety notices, urgent marine information — come over Channel 16 first, then refer you to a working channel.

The protocol when you hear a distress call is: listen, establish whether the Coast Guard has acknowledged (if so, don't transmit unless asked or unless you're the nearest vessel), and note the position. If the Coast Guard hasn't responded within 30 seconds, you respond.

Three distress classifications are worth knowing precisely. Mayday (from the French m'aidez) signals immediate danger to life. Pan-Pan (pahn-pahn) signals urgency — a safety concern that doesn't yet require immediate rescue, such as a medical emergency or a vessel that has lost steering. Sécurité (say-cure-ee-tay) is a navigational safety broadcast: a ship broadcasting its position leaving a harbor, a warning about a hazard. You'll hear Sécurité from the Coast Guard before transiting a narrow channel. The distinction matters because you respond differently to each.

When you make a Mayday call: say "Mayday Mayday Mayday," give your vessel name three times, your position (GPS coordinates or bearing/distance from a known point), the nature of distress, the number of people aboard, and any relevant information. Then listen. Don't transmit over a response.

DSC: Digital Selective Calling

Any VHF radio sold since 1999 in the US is required to have DSC capability. DSC allows you to send a formatted digital distress signal that transmits your vessel identity (MMSI number), GPS position, and distress type — all in a single button press — to every DSC-equipped receiver within range. The Coast Guard's network of DSC receivers covers most US coastal waters.

To use DSC effectively you need two things: an MMSI number (Maritime Mobile Service Identity — a nine-digit unique ID for your vessel) programmed into the radio, and a connection to a GPS receiver so the radio knows your position. Most modern fixed-mount VHF radios have internal GPS or accept an external NMEA feed.

The MMSI is free. US recreational boaters can register at BoatUS (boatus.com), Sea Tow, or the FCC. The registration links your MMSI to your vessel name, home port, and emergency contacts. When you press the DSC distress button and hold it for five seconds, the radio transmits your position and vessel ID. Any receiving station — including the Coast Guard — sees your GPS position immediately. This is categorically different from a voice Mayday where you're describing your position under stress.

Check your radio's menu. If the MMSI field reads 0000000 or is blank, it hasn't been programmed. This takes fifteen minutes and costs nothing.

Range Realities

VHF operates on line-of-sight propagation. The practical range from a fixed-mount antenna at the masthead of a 40-foot sailboat to a Coast Guard shore station antenna at height is typically 25–40 miles. Between two vessels at sea level, it's 5–10 miles depending on wave height and atmospheric conditions. The 25-watt power of a fixed-mount radio helps, but physics limits VHF to the horizon.

This is enough. The Coast Guard's VHF coverage along US coasts is comprehensive within normal cruising ranges. Offshore — beyond 50 miles from shore — you lose reliable VHF contact with shore stations, but nearby vessels may still hear you. For offshore passages, VHF is your primary short-range tool; HF/SSB or satellite covers the gap to shore-based rescuers.

Fixed Mount vs Handheld

A fixed-mount VHF runs 25 watts through a masthead antenna and gives you full range. A handheld runs 5–6 watts through a stub antenna and gives you maybe 5 miles in ideal conditions. These are not equivalent, and the handheld should not be your primary radio.

That said, carry a handheld. The waterproofing rating matters: IPX7 means submersion to 1 meter for 30 minutes. This is the minimum standard for a marine handheld — anything less will fail when it's dropped into the cockpit bilge in a rainstorm, let alone if you go overboard. The Standard Horizon HX890 and Icom IC-M94DE both carry IPX7 ratings and internal GPS with DSC capability. Battery life is typically 8–12 hours of standby.

The handheld goes in the grab bag, charged. If you have to abandon ship, you want a radio in the life raft. A fixed mount is permanently dead once the boat sinks.

AIS: Making Yourself Visible to Ships

AIS (Automatic Identification System) is a VHF-frequency transponder system used by commercial shipping. Every vessel over 300 GT is required to carry AIS. The system broadcasts the vessel's name, position, course, speed, and destination, received by any nearby AIS-equipped vessel or shore station.

A Class B AIS transponder for recreational vessels — the Vesper Cortex M1 or Garmin VHF 215i AIS are well-regarded units — transmits your position at 2-second intervals at low speed and 30-second intervals underway. Ships' officers watch AIS displays, not the horizon, for small vessel traffic. If you're not on their AIS display, you don't exist.

The alternative is a receive-only AIS antenna connected to your chartplotter, which shows you where ships are without broadcasting your position. This is better than nothing. It is not the same thing as being seen.

At $350–$700 for a Class B unit that integrates with most chartplotter networks, AIS is one of the highest-value safety investments on a coastal or offshore boat.

Weather: NOAA WX Channels

All US fixed-mount VHF radios include NOAA weather channels (WX1–WX10). Channel WX1 (162.550 MHz) covers most areas; the strongest local signal is the one to use. The broadcasts run continuously, 24 hours, updated every 1–6 hours depending on the station. The marine forecast format is standardized: conditions at sea, wave height, wind speed and direction, visibility, then an extended outlook.

The NOAA marine forecast is issued by zone, not by the GPS rectangle you're sailing through. Know your zone before departure — for example, "Coastal Waters from Pt. Conception to the Mexican Border" or "Chesapeake Bay, Sandy Point to Drum Point." The forecast may not match what you encounter on a specific point, but it's the baseline that everything else is measured against.

Many radios have a weather alert function that sounds an alarm when the NOAA network transmits a severe weather warning on the WX channels. Enable it. It goes off at 0300 when the forecast has changed, which is exactly when you want to know.

Offshore: SSB and Satellite

Beyond VHF range — roughly 50 miles offshore — your options are High Frequency (HF/SSB) radio, satellite communications, or silence. HF radio propagates via skywave reflection and can reliably reach 2,000+ miles; a 150-watt SSB radio with a proper ground plane can raise a ship or a net on the other side of an ocean. It requires an FCC ship station license (straightforward for US sailors) and some practice with propagation, but it's the reason offshore cruisers have conducted daily position check-ins for decades.

Iridium satellite phones (the 9575 Extreme is the current field standard) provide voice and SMS worldwide with no blackout zones. Monthly plans for occasional offshore use are available for $35–$75. For GRIB weather files and email, the Iridium GO! or the newer Iridium GO! Exec add data capability, though speeds are slow (2.4 kbps). Garmin inReach offers two-way text and tracking at lower cost but no voice.

For offshore passages, carry both an SSB (for nets, emergency contact, and weather) and a satellite communicator (for individual emergency contact and reliable two-way messaging). They serve different functions and neither fully replaces the other.