Electronics aboard

What each piece of gear does, how to use it, the rules that apply, and what to check when it misbehaves — or when you’re buying a boat that has it.

Communication

• Fixed-mount VHF radio with DSC
  The main radio on most boats: for calling other boats, marinas, bridges and the Coast Guard, and for hearing weather. The DSC part adds a red DISTRESS key that sends your boat's ID number (MMSI) and, if the radio has a GPS feed, your position, with one press.
• Handheld VHF radio
  A battery-powered marine VHF you can carry. It's the backup when the main radio or the boat's power fails, the radio for the dinghy or foredeck, and the one to grab for the life raft. Expect much less range than a fixed radio with a masthead antenna.
• Satellite messengers and communicators
  Handheld satellite devices that send and receive text messages, share your track and have an SOS button, far beyond cell and VHF range. They need a paid subscription, and their SOS goes to a private response centre rather than straight into the government satellite system EPIRBs and PLBs use.
• SSB / HF marine radio
  Marine single-sideband (SSB) radio uses medium and high frequencies to reach hundreds or thousands of miles, mainly for offshore cruisers. It also receives high-seas weather and weather-fax charts. It needs an FCC licence, a tuned antenna and a good ground.

Navigation

• AIS (Automatic Identification System)
  AIS lets vessels swap name, position, course and speed automatically by VHF radio. A receiver shows AIS-equipped ships on your plotter; a transponder also shows you to them. It's a big help near shipping lanes and in fog, but plenty of boats don't carry it.
• Electronic charts (NOAA ENC) and the end of NOAA paper charts
  Charts on a plotter, tablet or computer. The official US government charts are now NOAA's electronic navigational charts (ENCs); NOAA finished cancelling its traditional paper and raster charts in December 2024. You can still print paper charts from ENC data with NOAA's free Custom Chart tool.
• GPS receiver and chartplotter
  The GPS works out where you are from satellite signals; the chartplotter shows that position on an electronic chart with your course, speed and routes. On some boats they're one box; on others a separate GPS antenna feeds the plotter, VHF, autopilot and AIS.
• Radar
  Radar sends microwave pulses from a rotating antenna and shows echoes from boats, land, buoys and rain around you, day or night and in fog. It sees plenty that AIS can't, but small fiberglass and wooden boats can be weak targets, and it takes practice to read well.
• Depth sounder, transducers and fishfinder sonar
  A depth sounder times sound pulses bounced off the bottom to show the water under you; a fishfinder uses the same idea to draw the bottom and fish. The transducer, the sensor on or through the hull, makes or breaks it.
• Speed log and wind instruments
  A speed log measures your speed through the water, usually with a small paddlewheel under the hull. Wind instruments measure wind speed and angle at the masthead. With GPS and a compass, they let a sailor see true wind and how well the boat is sailing.
• Magnetic compass
  The steering compass needs no power and shows your heading instantly, even when every electronic box has failed. It's only as good as its correction: iron, magnets and live wiring near it cause errors called deviation that change as the boat turns.

Safety beacons

• EPIRB (406 MHz emergency beacon)
  An EPIRB is your boat's satellite distress beacon. Once switched on, it sends a coded 406 MHz alert through the international Cospas-Sarsat satellites to rescue authorities, giving the beacon's ID and, on GPS models, your position. It keeps transmitting for at least 48 hours.
• PLBs and AIS man-overboard beacons
  Two different personal beacons. A PLB is a pocket-sized 406 MHz satellite beacon, like a personal EPIRB, that alerts rescue authorities almost anywhere. An AIS man-overboard (MOB) beacon alerts your own boat and nearby boats, so the crew can turn back and find you quickly.

Networking

• NMEA 0183 and NMEA 2000 networking
  The wiring that lets your electronics share data: GPS position to the VHF and autopilot, depth and wind to the plotter, engine data to displays. Older gear usually talks NMEA 0183, one talker wired to its listeners. Newer gear uses NMEA 2000, a plug-together network on one backbone cable.

Monitoring

• Engine instruments, senders and alarms
  Gauges show oil pressure, coolant temperature, charging voltage, rpm and fuel; alarms (a lamp and buzzer) warn of low oil pressure or overheating. Each gauge reads a sender on the engine or tank, and most false readings come from senders, wiring and grounds rather than the gauge itself.
• Battery monitor (shunt-based)
  A battery monitor counts the amp-hours going into and out of your house batteries, so it can show state of charge, current draw and time remaining, which a voltmeter alone can't do reliably. It works through a shunt, a precise resistor fitted in the battery's main negative cable.
• Bilge high-water alarm
  A float switch set above the bilge pump's normal level that sounds a buzzer, light or horn if water keeps rising. It warns that the pump can't keep up or has failed, and it can save a boat, especially one left at the dock.

Autopilot

• Autopilot
  An autopilot steers for you, either holding a compass heading or following a route from the chartplotter. It needs a heading sensor (compass), usually a rudder position sensor, and a drive unit that turns the wheel, tiller or hydraulic steering.

General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.