+Vaisala 161-taitto 17.1.2003 15:15 Sivu 16

Veli-Matti Miettinen, M.Sc. (Eng.) Application Manager Wind Sensors Vaisala

Vaisala WAS425AH Ultrasonic Wind Sensors Supporting the Finnish

“Squadron 2000” of the Finnish Navy uses Vaisala WAS425AH Ultra- sonic Wind Sensors to support its operations at sea. Ultrasonic Wind Sensors are incorporated into the ships’ navigation systems both in the fast attack craft and the of the squadron. The harsh conditions on the northern seas set stringent requirements for wind sensors - met by the Vaisala Ultrasonic Wind Sensor.

ince 1998 the Finnish ed into the ships’ navigation sys- hovercraft participate in normal Navy has been building tems both in the fast attack craft Navy operations, in other words S up “Squadron 2000”, a and the hovercraft of Squadron they defend territorial integrity new squadron made up of two 2000. and carry out major exercises. A fast attack craft and four hover- The harsh conditions on Vaisala MILOS Weather Station craft. The squadron currently op- northern seas set high require- has been providing reliable erates one fast attack craft and ments for wind sensors. Accord- weather data since 1998 for the one hovercraft. Squadron 2000 ing to Navy officers, Vaisala Ultra- existing fast attack craft of relies on Vaisala WAS425AH Ul- sonic Wind Sensor WAS425AH Squadron 2000. Its First Officer trasonic Wind Sensors for wind is the first wind sensor that oper- explains: “To measure wind measurement onboard these ves- ates satisfactorily on these ships. speed and direction is vital for sels. Ultrasonics are incorporat- The Vaisala WAS425AH is a solid two reasons. Craft need the state wind sensor that uses ultra- wind, relative humidity and sound to determine horizontal barometric pressure data for usu- Staff of the fast attack craft appreciates the wind data and wind speed and direction. The al navigation. The second rea- weather data that Vaisala measurement principle is based son, especially important for equipment provides. on transit time: the time it takes warships, is the fact that ballistic for the ultrasound to travel from preparation is needed for ar- one transducer to another, de- tillery and missile firing. Wind, pending on wind speed along the relative humidity and baromet- ultrasonic path. The WAS425AH ric pressure conditions are essen- is heated and has thermostatically tial parameters to be considered controlled heaters in the trans- for ballistic preparation. The ducer heads to prevent freezing more accurate the weather data, rain or snow from building up on the more successful the ballistic the sensor. preparation. This means that less corrections will then be needed Measuring wind speed during firing.” and direction At the craft, digital wind data is essential is transferred from WAS425AH In peacetime fast attack craft and to the MILOS as an NMEA

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The Finnish Navy’s fast attack craft at sea.

Standard message. The craft’s mum speed of the fast attack out any main- navigation system gets the weath- craft is 18 m/s, whereas the hov- tenance. The er data from MILOS and passes ercraft reaches 25 m/s. In the fast sensor is fas- it on via the craft’s local network attack craft a continuous true tened with a to the fire control system. It is al- wind as high as 30 m/s has been rigid bar so possible to transmit weather measured on the Baltic Sea. Be- on top of the data to other craft. In the existing side the weather conditions, fac- craft. The in- hovercraft there is no weather tors such as the movement, tilt- stallation and station, and its navigation system ing and vibrations of the craft set the sensor itself takes care of wind data process- high demands on the wind sen- have been robust ing. As a backup measure these sors. Temperature and relative enough to bear the me- craft use portable wind meters. humidity variations are also vast chanical stress. Heaters in Mainly true wind data is during the year. In the winter, the transducer heads prevent used in these craft. They meas- when the craft sails at a high ve- freezing rain or snow build-up. ure true wind to be able to esti- locity, the wind sensor can face High accuracy and reliable op- mate the effect of the weather on temperatures lower than -30°C eration in all weather condi- operations. Relative wind data is (-22 °F). tions are the features of Ultra- also of interest as it is needed, sonic that the crew appreciates for example, for steering in har- Positive long-term user the most. ● bors. experiences The crew of the fast attack craft is Extreme conditions on more than pleased with their Ul- northern seas trasonic Wind Sensor and MI- The sensors installed on top of LOS Weather Station. As the the craft are under enormous First Officer of the craft said: strain due to harsh conditions at “Ultrasonic is the first wind sen- sea, especially in the winter. sor that withstands all the chal- The Vaisala WAS425 Ultrasonic Snow and salt water spraying on lenging conditions of the Baltic Wind Sensor has no moving parts, the sensor can cause, for exam- Sea all year round”. So far the Ul- and is resistant to contamination ple, corrosion, ice formation and trasonic has functioned as re- and corrosion. This eliminates on- mechanical damage. The maxi- quired for close to 5 years with- demand and periodic maintenance.

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