NavigationNAU 102Lesson 29

Weather InstrumentsThe safety of crew, passengers, cargo and the ship itself is dependent on making good weather decisions.Weather has a significant impact on every voyage.

Weather InstrumentsWe are our own weather station at sea.We must develop an accurate forecast using data received from shore and that we collect ourselves.Youll learn how to make a forecast in Meteorology.

Duties of the MateAt all times, be knowledgeable of the current weather.Wind direction and speedWave direction and heightVisibilityTrend of the barometer

Duties of the MateAt all times, be knowledgeable of the weather forecast.Obtain 24 hour forecast from weather fax, messages, etc.Interpret the forecast for your area.When necessary, make your own forecast.

Weather InstrumentsSatellitesMeteorological data is collected by: BuoysShips (thats you)

Duties of the MateConduct marine surface weather observations.Make observationsLog observationsTransmit observations to National Weather Service

Duties of the MateConduct marine surface weather observations.4 times each day0000, 0600, 1200, 1800 GMTVoluntary program7000+ ships worldwide (600 US)

Weather ObservationsData is collected and formatted in accordance with the Marine Observers Handbook.http://www.nws.noaa.gov/om/marine/handbk1.pdf

Weather InstrumentsAneroid BarometerMeasures atmospheric pressure.Air pressure exerts a crushing force on a thin metal element.Linkages move to a pointer to indicate the pressure on a scale.

Aneroid Barometer

Aneroid BarometerMust be properly adjusted.(Usually done by a professional, often for free.)Reading must be adjusted for elevation to give pressure at sea level.(Note: Mercurial Barometers must also be corrected for latitude and temperature.)

Barometers

Weather InstrumentsBarographA recording barometer.

Weather InstrumentsThermometerMeasures air temperature.You must be able to convert between Celsius and Fahrenheit scales.

Temperature Conversions

Temperature Conversions

Weather InstrumentsHygrometerMeasures Relative Humidity and Dew Point.

Weather InstrumentsRelative Humidity ratio of amount of water vapor in the air to the amount it could hold at the current temperature.Dew Point the temperature at which water vapor will condense.

Weather InstrumentsHygrometerMost common type: sling psychrometer.

Sling PsychrometerTwo Thermometers: 1 wet, 1 dryTemperature difference is noted.

Sling Psychrometer

Psychrometer

Weather InstrumentsWind VaneMeasures apparent wind direction.Measures apparent wind speed.Anemometer

Weather InstrumentsWind VaneAnemometer

WindDefinitionsApparent wind. The speed and direction (true or relative) from which the wind appears to blow with reference to a moving point.True wind. The speed and direction from which the wind blows with reference to a fixed point.

WindExamplesApparent wind: From 090 T (000 R), 15 knots. True wind: East wind, 10 knots.Ship: course 090 T, speed 5 knots.

WindExamplesApparent wind: 270 T (180 R), 5 knots. True wind: West wind, 10 knots.Ship: course 090 T, speed 5 knots.

WindAnemometers and wind vanes give apparent wind (unless the vessel is stopped).We must solve for True wind for our weather observations.Best done graphically on maneuvering board, plotting sheet or compass rose.

WindExample 1: A ship is proceeding on course 240 at a speed of 18 knots. The apparent wind is from 040 relative at 30 knots. What is the true wind?

WindStep 1: Plot ships course & speed.

WindStep 2: Convert relative direction of apparent wind to true direction, if necessary.Example 1: A ship is proceeding on course 240 at a speed of 18 knots. The apparent wind is from 040 relative at 30 knots.R + S = T040 R + 240 = 280 T

WindStep 3: Draw the apparent wind from the tip of the ships course & speed vector.(Remember, draw the direction the wind is blowing towards!)

WindStep 4: Complete the triangle. Result = True wind.Direction = 315 TSpeed = 20 knots

Wind MeasurementBeaufort ScaleIf no instruments are available, speed may be estimated by observing the effect on the water.Scale was devised in 1806 by English Admiral Sir Francis Beaufort (1774-1857).

Force 0

Force 1

Force 2

Force 3

Force 4

Force 5

Force 6

Force 7

Force 8

Force 9

Force 10

Force 11

Force 12

Introduction to NavigationQuestions?