Weather Instruments

What sets bridge weather instruments apart

Weather instruments are the ship's own local sensors, distinct from the forecasts and warnings received over NAVTEX or satellite weather services. A barometer trend over the last three hours often gives an officer of the watch earlier warning of a developing system than the next scheduled forecast broadcast, and a true wind reading corrected for the ship's own heading and speed is something no shore forecast can substitute for when planning cargo operations or a course alteration.

Main components

Anemometer

A rotating-cup or ultrasonic sensor mounted clear of the ship's structure, typically on the monkey island, feeding apparent wind speed and direction to a bridge display that calculates true wind by removing the vessel's own course and speed vector.

Barometer

An aneroid or digital pressure sensor, read regularly and logged so the trend, not just the instantaneous value, is available to the watch officer.

Thermometer

Air temperature and, separately, sea temperature sensors; sea temperature also feeds engine room cooling water planning and, on some trades, cargo temperature management.

Hygrometer

Measures relative humidity, used together with air and sea temperature to judge fog risk and, on some cargoes, condensation (ship's sweat) risk in holds.

Selection and sizing

Selection turns on mounting location and integration rather than a performance spec war: the anemometer needs a position clear of funnel and superstructure turbulence to give a representative reading, and the whole set benefits from feeding a common bridge display or the ship's INS rather than standing as isolated dial instruments nobody logs consistently. Redundant sensors matter less here than reliable calibration and a location free of airflow disturbance.

Regulations and class

SOLAS Chapter V requires ships to have on board, or to have access to, means of measuring and displaying wind speed and direction, together with means of measuring and recording atmospheric pressure, air and sea temperature — the goal is that a bridge team always has current local weather data available, whether from dedicated instruments or an integrated bridge system. Class notations for enhanced bridge equipment may specify calibration intervals and accuracy tolerances beyond the SOLAS minimum.

Typical faults

• Anemometer sited in turbulent airflow — readings are consistently biased and the crew learns to distrust the display, defeating its purpose.
• Barometer never logged consistently — the pressure trend that gives early warning of a developing system is lost even though the instantaneous reading is available.
• Iced or fouled anemometer cups — stops rotating in freezing spray without an obvious fault indication on the bridge display.
• Uncalibrated humidity sensor — leads to missed condensation risk warnings in holds carrying moisture-sensitive cargo.

What to look for in a supplier

• Sensor housings rated for the vessel's mast-head or monkey-island exposure, including salt spray and, on some trades, icing.
• Integration compatibility with the existing bridge display or INS, rather than a standalone dial nobody references.
• A stated calibration interval and an accessible way for crew to verify readings against a known reference.
• Documented accuracy figures for wind speed, pressure and temperature, not only a working range.

Log the barometer reading at fixed intervals even when nothing looks unusual — the three-hour pressure trend is often the first hint of deteriorating weather, well before any forecast update arrives.