4.14 Radar Basics & Marine Radio (VHF)

Radar and Radio Complete the Electronic Bridge

Section 4.13 covered GPS, plotters, depth, and AIS. This section covers radar for ranging targets and VHF radio for distress, urgency, and bridge-to-bridge coordination — core Q162 instruments topics and daily tools on any Master 100 passenger vessel that runs in fog, traffic, or beyond shouting distance of the dock.

Radar Basics — Range and Bearing

Marine radar transmits microwave pulses and listens for echoes. From the echo it measures:

• Range — distance to the target (from time delay of the return)
• Bearing — direction of the target relative to the ship’s heading (or stabilized north-up display)

On the PPI (plan position indicator) display, your vessel is typically at the center (or offset); targets appear as blips or ARPA/AIS-linked symbols at the correct range and relative bearing. Modes you will meet:

Relative motion (exam-level)

Even without full ARPA training, understand relative motion: the way a target appears to move on the screen is the combination of your motion and the target’s motion. A target that stays on a steady relative bearing while range decreases is a classic collision risk cue (same idea as Rule 7 compass bearing steadying). Radar helps you detect that early in haze and at night; it does not decide stand-on/give-way for you — COLREGS still do.

Range rings and VRM/EBL (variable range marker / electronic bearing line) tools measure distance and bearing to a selected echo. Use them to fix approximate distance off a jetty, pick up a buoy in haze, or track a ferry’s CPA conceptually.

Clutter: Sea and Rain

Radar sees more than ships:

• Sea clutter — returns from waves, worst near own ship in rough water; use sea clutter / STC controls carefully so you reduce near-range noise without wiping out small targets
• Rain clutter — returns from precipitation cells; use rain clutter / FTC controls to see through rain squalls without erasing real targets inside the storm
• Gain — too high floods the screen; too low loses weak targets

Master practice: adjust clutter for the conditions, then re-check that known targets (a buoy you can still see, a pier end) still paint. “Cleared the screen” is not a victory if you also cleared the freighter.

Radar in Fog — Powerful, Not Sufficient Alone

Radar is one of the best tools in restricted visibility, but Rule 5 (Lookout) still requires a lookout by sight and hearing as well as by all available means appropriate in the prevailing circumstances. Exam and real-world traps:

• Treating radar as the only lookout while the watchstander stares at the plotter with headphones on
• Assuming every hazard paints (low wooden boats, ice, debris, and some buoys can be poor targets)
• Running unsafe speed (Rule 6) because “radar is on”
• Ignoring sound signals (Rule 35) because the radar looks empty

Correct posture in fog: reduced speed appropriate to visibility and traffic, radar and AIS if fitted, listening watch, sound signals as required, VHF bridge-to-bridge when useful, and readiness to stop or maneuver. Radar supplements the lookout; it does not replace Rule 5 or Rule 19 conduct.

Marine VHF — Channels Masters Live On

VHF-FM marine radio is line-of-sight, ship-to-ship and ship-to-shore communication. Know these channels cold:

Watchkeeping habits:

• Maintain a proper listening watch on 16 as required for your vessel and as good practice when underway
• Keep calls on 16 short; move to a working channel for long conversation
• Use 13 for navigational bridge-to-bridge when that is the correct local practice for the traffic situation
• Monitor WX before departure and when weather is changing (see storm-warning section of Nav Gen)

False distress or hoax maydays are federal crimes; never “test” with a fake Mayday.

Radio Procedure — Mayday and Pan-Pan

Speak slowly, clearly, and in a standard pattern. You will not be graded on poetry; you will be graded on getting help and not crying wolf.

Mayday (distress)

Use Mayday when a vessel or person is in grave and imminent danger and needs immediate assistance (sinking, fire out of control, person overboard in extreme conditions with life at risk, etc.).

Typical spoken pattern (adapt to time and capability):

1. “Mayday, Mayday, Mayday”
2. This is [vessel name / call sign], repeated
3. Position (lat/long, or bearing/distance from a known point, or AIS-reported position)
4. Nature of distress (sinking, fire, flooding, medical…)
5. Assistance required and number of persons on board
6. Other useful info (description, intentions, channel guard)
7. Repeat as needed; listen for acknowledgment from USCG or another vessel

Transmit on VHF 16 (and use DSC distress if equipped — below). If you hear a Mayday and the Coast Guard does not answer, you may need to relay.

Pan-Pan (urgency)

Use Pan-Pan (pronounced “pahn-pahn”) for urgent messages concerning the safety of a vessel or person when the situation is serious but not yet grave and imminent distress — e.g., loss of steering with no immediate grounding risk, a medical issue that needs advice/evac planning, or a disabled vessel not currently sinking.

Pattern parallels Mayday: “Pan-Pan, Pan-Pan, Pan-Pan,” identity, position, nature of urgency, assistance needed.

Sécurité

Sécurité (say-cure-e-tay) prefixes important safety navigational or weather information (hazard to navigation broadcast, etc.). Less common as a Master 100 “own emergency” tool than Mayday/Pan-Pan, but recognize it on the air.

DSC Overview

Digital Selective Calling (DSC) is a digital alerting system built into many modern fixed-mount VHFs (and MF/HF systems on larger vessels). At Master 100 level know:

• DSC can send a distress alert with your MMSI and, if the radio is interfaced to GPS, your position — often with a dedicated DISTRESS button under a cover
• DSC can also place routine, safety, and urgency digital calls to specific MMSIs or groups
• After a DSC distress alert, voice follow-up on the associated distress channel (for VHF, Channel 16) is the normal operational picture
• Your radio must be programmed with a valid MMSI and preferably GPS-fed to be fully useful; an unprogrammed DSC radio is a wasted safety feature

Do not practice with live distress alerts. Use test procedures only as the manufacturer and regulations allow.

GMDSS Awareness (Master 100 Depth — Not Unlimited)

GMDSS (Global Maritime Distress and Safety System) is the international framework that combines DSC, satellite alerting, MSI (maritime safety information), EPIRBs, SARTs, and watch systems so a distress alert reaches shore and other ships. Unlimited/oceangoing licenses dive deep into sea areas A1–A4 and carriage matrices.

For Master Less Than 100 GRT near coastal, exam and operational awareness means:

• Understand that coastal safety depends on VHF, DSC, Weather/MSI broadcasts, and EPIRB/PLB concepts as fitted
• Know Mayday / Pan-Pan / Channel 16 / DSC distress as your working toolkit
• Do not pretend you need a full radio officer’s GMDSS GOC syllabus to pass Master 100 Nav Gen — but do not answer that “VHF is obsolete because of GMDSS satellites” either

If the vessel carries an EPIRB, know that it is a satellite distress beacon for locating the vessel/survival craft — registration and hydrostatic release maintenance matter operationally even when Nav Gen only sketches the concept.

Antenna and Power Basics

VHF range is roughly line of sight, improved by antenna height and adequate power:

• Antenna: mount as high as practical, vertical, with a clear view; a damaged coax, corroded connector, or horizontal whip kills range
• Power: fixed VHF often selectable 1 W / 25 W (low/high). Use low power for short-range marina chatter when appropriate; use high power for distress, hailing at distance, and when low power fails
• Handhelds are excellent backups and tender radios but have lower antennas and power — do not assume a handheld equals a fixed 25 W set on the flybridge
• Keep a spare fuse, know the breaker, and test the radio before departure, not after the engine room fills with smoke

Radar scanners also need clear mounting (minimize blind sectors from masts) and proper power; a radar that never gets a pre-underway check is décor.

Radar & radio pocket card

1. Radar → range + bearing; relative motion can show collision risk (steady bearing, decreasing range).
2. Adjust sea/rain clutter and gain without erasing real targets.
3. Fog: radar helps; Rule 5 + safe speed + sound signals still apply.
4. 16 distress/safety/calling; 13 bridge-to-bridge; WX weather.
5. Mayday = grave/imminent + immediate help; Pan-Pan = urgency.
6. DSC distress + MMSI/GPS; voice on 16; no fake distress.
7. GMDSS = coastal safety system awareness; VHF remains core for Master 100.
8. Antenna height + power + good coax = usable radio range.

Electronics and radio do not make a master; they make a prepared master faster. On Q162, name the channel, the distress word, the radar limit, and the Rule 5 truth — then run the boat the same way when the inlet disappears into gray.