5.2 Maritime Phonetic Numbering System & Position Reporting Formats

5.2 Maritime Phonetic Numbering System & Position Reporting Formats

Numerical data forms the backbone of maritime VHF transmissions. Whether stating a vessel's position during a Mayday distress call, identifying a working channel, reporting water depth, or transmitting a 9-digit Maritime Mobile Service Identity (MMSI), precise numerical transmission is critical to safety of life at sea.

To prevent numbers from being garbled over low-fidelity VHF voice channels, the ITU Maritime Radio Regulations specify standardized phonetic pronunciations for all digits, decimal points, and large numerical modifiers. Furthermore, strict formatting rules govern how geographical positions must be constructed and spoken.

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Standardized Phonetic Digit Pronunciations

When speaking numbers over maritime VHF radio, ordinary conversational pronunciations are replaced by deliberate phonetic sounds. Certain digits are altered specifically to avoid confusion across international accent barriers (for instance, three is spoken as TREE to prevent non-native speakers from producing a soft 'th' sound, and five is spoken as FIFE to avoid confusion with nine or fire).

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Rules for Transmitting Digits & Numbers

1. Digit-by-Digit Transmission: As a general rule, all multi-digit numbers—including VHF channel numbers, MMSI numbers, call signs, positions, bearings, and speeds—must be spoken digit by digit.

   • VHF Channel 72: Spoken as "Channel SEV-EN TOO" (never "Channel seventy-two").
   • VHF Channel 16: Spoken as "Channel WUN SIX" (never "Channel sixteen").
   • MMSI 235012345: Spoken as "TOO TREE FIFE ZEE-RO WUN TOO TREE FOW-ER FIFE".

2. Round Hundreds and Thousands Exception: Whole hundreds and thousands may be spoken using HUNDRED and TOUSAND.

   • Distance 500 metres: Spoken as "FIFE HUN-DRED metres".
   • Altitude 1,000 feet: Spoken as "WUN TOO-ZAND feet".
   • Course 12,000: Spoken as "WUN TOO TOO-ZAND".

3. Decimal Point Pronunciation: When transmitting decimal numbers, such as VHF frequencies or exact coordinates, the word DECIMAL (DAY-SEE-MAL) must be inserted.

   • Frequency 156.8 MHz: Spoken as "WUN FIFE SIX DECIMAL AIT Megahertz".
   • Latitude 50°45.2' N: Spoken as "FIFE ZEE-RO degrees FOW-ER FIFE DECIMAL TOO minutes North".

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Position Reporting Format 1: Latitude & Longitude

In maritime safety communications (such as Mayday, Pan Pan, or Securite broadcasts), the primary method of reporting position is by Latitude and Longitude.

Formatting Rules for Latitude and Longitude:

• Order of Transmission: Latitude is always spoken FIRST, followed by Longitude.
• Latitude Format: Expressed in degrees and minutes (plus decimal fractions of a minute if available), followed by the cardinal direction North or South.
  • Latitude degrees are expressed as 2 digits (00 to 90).
  • Example: 50°45' N -> "50 degrees 45 minutes North" (Phonetic: "FIFE ZEE-RO degrees FOW-ER FIFE minutes NORTH").
• Longitude Format: Expressed in degrees and minutes, followed by East or West.
  • Longitude degrees must ALWAYS be expressed as 3 digits (000 to 180). This extra leading zero is critical to prevent confusion between latitude and longitude.
  • Example: 001°15' W -> "001 degree 15 minutes West" (Phonetic: "ZEE-RO ZEE-RO WUN degrees WUN FIFE minutes WEST").

Standard Position Callout Example:
"My position is Latitude Five Zero degrees Four Five minutes North,
 Longitude Zero Zero One degree One Five minutes West."

Exam Warning: Omitting the leading zero in longitude (e.g., saying "1 degree 15 minutes West" instead of "001 degree 15 minutes West") is a major error in the RYA SRC examination.

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Position Reporting Format 2: Bearing & Distance from a Landmark

When GPS coordinates are unavailable, or when providing immediate tactical awareness to a nearby lifeboat or coastguard station, position can be reported as a Bearing and Distance from a prominent, charted landmark.

Formatting Rules for Bearing and Distance:

1. Bearing: Stated in degrees True (3-digit format from 000 to 350 degrees) from the landmark to the vessel.
2. Landmark: Must be a recognized, fixed, unambiguous object shown on Admiralty charts (e.g., lighthouse, headland, cardinal buoy, windfarm platform).
3. Distance: Stated in nautical miles (or cables for very short distances).

Structure & Standard Script:

[BEARING IN DEGREES TRUE] + "degrees True from" + [NAME OF LANDMARK] + "distance" + [DISTANCE IN NAUTICAL MILES] + "miles"

Example 1: "Bearing 180 degrees True from Needles Lighthouse, distance 3 miles"
Phonetic: "WUN AIT ZEE-RO degrees True from Needles Lighthouse, distance TREE miles."

Example 2: "Bearing 045 degrees True from Anvil Point, distance 12 miles"
Phonetic: "ZEE-RO FOW-ER FIFE degrees True from Anvil Point, distance WUN TOO miles."

Notice that bearings are expressed as 3 digits (e.g., 045 as "ZEE-RO FOW-ER FIFE"), and the reference point is specified clearly. Using these exact formats ensures search and rescue assets can plot your position within seconds on their digital charting displays.