Weather Monitoring Systems

What the sensors measure and who uses the data

• Ultrasonic anemometers time sound pulses between transducers to give wind speed and direction with no moving parts. Cup and vane sensors do it mechanically.
• Digital barometers give station pressure, which the software reduces to QNH and QFE for the helicopter.
• Temperature and humidity probes give dew point.
• Forward-scatter sensors estimate visibility and present weather from light scattered by fog, rain or snow.
• Ceilometers fire a laser upward and time the return to find cloud base.

Three users take the data. The helicopter landing officer and the pilot use it for the landing decision. The DP system uses wind speed and direction as feed-forward, so the thrusters react before the wind moves the hull. The bridge and the marine superintendent use it for crane, anchor-handling and transfer limits.

A helideck monitoring system adds motion. It takes roll, pitch and heave from an MRU and reports helideck inclination and heave rate to the pilot.

Key specifications

Standards and what a used system must meet

In the UK sector, CAP 437 sets the helideck standard, and the Helideck Certification Agency (HCA) inspects and certifies helidecks. CAP 437 expects automated measurement of wind speed and direction, temperature, dew point, QNH, QFE, cloud, visibility and present weather, and a motion system on moving helidecks. Other regions name their own standard and certifying body, often based on CAP 437. The WMO's Guide to Instruments and Methods of Observation (WMO-No. 8) is the usual reference for sensor performance and siting. Sensors on the derrick or crane booms need hazardous-area certification under IEC 60079.

What counts for a used system is the software. When CAP 437 changes, OEMs release new software to match. A system on old software may need an upgrade before the certifying body accepts it on your helideck.

Failure modes and inspection

• Cup and vane bearings wear fast in salt air. Ultrasonic sensors lose accuracy when the transducer faces foul, ice up or get damaged by birds.
• Barometers and humidity probes drift.
• Optical windows on visibility and cloud sensors salt up.
• A wind sensor mounted off north reports the wrong direction, and turbulence from the derrick or accommodation skews readings.

Ask for calibration certificates for the barometer and humidity probe and the date of each. A survey checks wind direction alignment against vessel heading, compares readings with a reference instrument, cleans and tests the optics, and reviews the software's version and event log.

Documentation

• Calibration certificates with dates for each sensor.
• Software version and the CAP 437 edition it claims to meet.
• The last helideck certification or HCA inspection report for the source unit.
• Hazardous-area certificates for sensors in classified zones.
• Siting drawing showing sensor positions and heights.

Integration with your unit

True wind needs heading and speed, so the system takes inputs from your gyrocompass and GNSS. The helideck motion page needs an MRU input in the format the software reads. Outputs go to the DP controller, often as IEC 61162 MWV sentences, and to the radio room, helideck displays and the helicopter operator onshore. Siting is the hard part on a new unit. Sensors need clean airflow, which may mean a new mast position and a fresh airflow assessment.

Refurbishment, used or surplus

Replacing a failed anemometer or barometer with the same model keeps an accepted system in service with no new paperwork. A complete used helideck system makes sense only if the OEM will upgrade its software to the current standard. Unused surplus sensors are a good buy when the calibration is recent or the OEM will recalibrate them.

Related equipment

Helideck motion comes from motion reference units. Weather data often goes onshore over data communication links. Naventr can request the calibration certificates from the Seller for you.