20.4 Survival Craft Electronics, FAX & NAVTEX

20.4 Survival Craft Electronics, NAVTEX & NMEA

Quick Answer: SART = 9 GHz, replies after ON when radar interrogates → ~12 dots. EPIRB = primary 406 MHz locating beacon with unique hex ID. Weatherfax = printed pictures; 120 lines/min; filter ~1 kHz @ −6 dB. NAVTEX = MSI via SITOR-B/FEC on 518 kHz; reject subjects by programming. NMEA 0183 shield grounds at talker; NMEA 2000 = multi-talker network, LEN 1 = 50 mA, 1.5 V drop budget.

Key topics 087 (Survival Craft: VHF, SARTs & EPIRBs), 088 (FAX, NAVTEX), and 089 (NMEA Data) finish the marine technology cluster. When the ship is in distress—or when the bridge needs weather and position data—these systems are the technical backbone.

SART — Search and Rescue Radar Transponder

Activation and transmission logic

What causes the SART to begin a transmission? After being activated, the SART responds to RADAR interrogation. It is not a free-running always-on beacon the moment it is wet, and it is not “keyed like a microphone” for each reply. Survivors switch it ON; 9 GHz X-band ship radars interrogate it; the SART replies.

Homing picture

On the rescuer’s PPI, the line of dots points along the bearing to the survival craft. As range decreases, the presentation evolves (arcs/circles on many displays)—Element 3’s tested image remains twelve equally spaced dots. Hold/mount the SART high for line-of-sight microwave range (operational doctrine reinforced in Element 1).

EPIRB — primary locating signal source

Which GMDSS equipment is the primary source of transmitting locating signals?

An EPIRB transmitting on 406 MHz—not an RDF, not a “SART on 406 MHz,” and not the survival-craft VHF transceiver as the primary satellite locating answer.

Coded identity and position support

True statement concerning satellite EPIRBs: Once activated, these EPIRBs transmit a signal for use in identifying the vessel and for determining the position of the beacon.

True statement regarding 406 MHz EPIRB transmissions: they transmit a unique hexadecimal identification number.

Maintainer tasks: register the beacon correctly, inspect hydrostatic release and battery dates, use self-test only, and after any real activation plan battery service. False alerts → notify Coast Guard / RCC immediately (Element 1 discipline still applies).

Facsimile (weatherfax)

What is facsimile?

Facsimile is the transmission of printed pictures for permanent display on paper—not slow-scan TV as the definition, not RTTY characters that “happen to look like a picture,” and not ordinary broadcast television.

HF weatherfax parameters

Install/repair notes:

1. Receiver bandwidth too wide → noisy gray images; too narrow → lost detail.
2. Wrong USB/LSB or BFO offset → black/white inversion or tearing.
3. Confirm schedule/frequency lists for the ocean area; the radio path is still ionospheric HF.

NAVTEX — MSI by narrow-band direct printing

NAVTEX delivers Maritime Safety Information (MSI)—navigational warnings, weather, and related safety text—to a dedicated receiver/printer or display.

Mode and frequency

NAVTEX is a receive service for the ship on 518 kHz (with other regional frequencies such as 490 kHz in broader practice). The vessel does not “answer” NAVTEX like an ARQ telex call.

Message filtering

What determines whether a NAVTEX receiver does not print a particular type of message content? The subject indicator matches that programmed for rejection by the operator.

Operators program which B1 transmitter IDs and B2 subject categories to accept or reject (always-print categories such as certain distress/navigational warnings may still force print depending on rules/equipment—Element 3’s tested mechanism is subject-indicator rejection programming).

NMEA data — interfacing GPS, radios, and instruments

Marine electronics share data over NMEA networks. Element 3 contrasts classic NMEA 0183 with modern NMEA 2000 and tests installation numbers maintainers must memorize.

NMEA 0183 vs NMEA 2000

Shield grounding on NMEA 0183

How should shielding be grounded on an NMEA 0183 data line? Terminated to ground at the talker and unterminated at the listener. Grounding both ends invites ground loops; grounding only the listener is the wrong pool choice.

NMEA 2000 network behavior and power

LEN math: sum device LENs × 50 mA ≈ network load; size power feeds and backbone length so the end-of-line drop ≤ 1.5 V under load. Mid-powered or multiple power insertion points appear on large yachts—but the pool’s single-location method answer is end-powered.

GPS → radio path (ties §20.3)

A correct NMEA install is why the DSC VHF shows lat/long:

1. GNSS sensor talks 0183 sentences (e.g. RMC/GGA family) or N2K PGNs.
2. Wiring polarity and baud (commonly 4800 for classic 0183) must match.
3. Shield grounded at talker only for 0183.
4. Radio display confirms position before the ship sails.

Survival + MSI + data: one safety stack

Exam-day checklist (3-N 087–089)

1. SART: activate → reply to radar; band 9 GHz; display 12 dots.
2. Primary locating transmitter: 406 MHz EPIRB; unique hex ID; signal supports ID + position determination.
3. Facsimile = printed pictures on paper; weatherfax 120 LPM; filter 1 kHz @ −6 dB.
4. NAVTEX: SITOR-B/FEC; 518 kHz international; filter by subject indicator rejection.
5. Bi-directional multi-talker network language: NMEA 2000 (not 0183).
6. 0183 shield: ground at talker, open at listener.
7. N2K: device failure doesn’t kill others; LEN 1 = 50 mA; single-location end-powered; 1.5 V drop budget.

Master the three survival layers, the two MSI receivers (fax + NAVTEX), and the NMEA install rules—and Topic 3-N (082–089 with 3-M) is complete for Element 3 marine communications technology. Radar and satellite systems continue in the following chapters.