Candidates most commonly fail on this topic by listing instruments they recognise without being able to explain what each measures, how to read it correctly, or — critically — how to integrate multiple sources of meteorological information into an actual passage planning or watchkeeping decision. Examiners probe beyond the list.
The core question behind every examiner question here: How do you obtain met information, what do you do with it, and what does it tell you about the weather you are about to enter?
Obtaining Meteorological Information
Sources used in practice and expected in an oral:
- NAVTEX — automated broadcast of MSI including gale warnings, forecasts and coastal weather reports on 518 kHz (international) and 490 kHz (national English language). Range typically covers the relevant sea area.
- Weatherfax (WEFAX) — HF radio facsimile charts showing synoptic pressure patterns, fronts and forecast positions. Requires interpretation of isobars, fronts and pressure gradient.
- VHF coast radio / MCA Coastguard — broadcast weather on working channels at scheduled times; also available on request on working channels.
- Inmarsat / satellite services — GMDSS vessels can receive MSI via SafetyNET (EGC on Inmarsat-C). Provides ocean-area forecasts.
- Commercial routing and weather routing services — grib files, routed forecasts (PredictWind, Expedition, etc.); common on yachts but a candidate must understand these are not SOLAS MSI sources.
- Port authority / harbour master — local knowledge and localised forecasts.
- Met office forecasts via internet — useful but must be used alongside official broadcasts.
Shipboard Meteorological Instruments
Candidates must know what each measures and its significance:
- Barometer / barograph — atmospheric pressure; the trend and rate of change is more useful than the absolute value. A rapid fall (typically 3 hPa or more in 3 hours — SME: confirm threshold) indicates approaching storm or deepening depression.
- Thermometer (dry bulb) — air temperature.
- Hygrometer / wet and dry bulb thermometer (psychrometer) — relative humidity and dew point; dew point close to air temperature indicates fog risk.
- Anemometer — wind speed; anemograph records it over time.
- Wind vane — wind direction. Backing vs. veering indicates frontal passage or pressure system movement.
- Barothermograph / combined instruments — records both pressure and temperature traces.
- Sea temperature (SST) sensor — sudden change may indicate current boundaries or fog risk (warm air over cold water).
Integrating the Information
On passage, the OOW is expected to:
- Monitor barometric tendency every watch.
- Cross-check shipboard observations against received forecasts.
- Recognise discrepancies — if the barometer is falling faster than the forecast suggests, treat it as a warning.
- Log weather observations and update the master and, where required, pass observations to met services.
The syllabus underpinned by MSN 1858 assesses meteorology as a core competency for safe watchkeeping and passage planning.