Transcript Lesson 29 - Weather Instruments

Navigation
NAU 102
Lesson 29
Weather Instruments
Weather has a significant impact on
every voyage.
The safety of crew, passengers, cargo
and the ship itself is dependent on
making good weather decisions.
Weather Instruments
We are our own weather station at sea.
We must develop an accurate
forecast using data received from
shore and that we collect ourselves.
You’ll learn how to make a forecast
in Meteorology.
Duties of the Mate
At all times, be knowledgeable of the
current weather.
•Wind direction and speed
•Wave direction and height
•Visibility
•Trend of the barometer
Duties of the Mate
At 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 Instruments
Meteorological data is collected by:
Satellites
Ships (that’s you)
Buoys
Duties of the Mate
Conduct marine surface weather
observations.
•Make observations
•Log observations
•Transmit observations to National
Weather Service
Duties of the Mate
Conduct marine surface weather
observations.
Voluntary program
7000+ ships worldwide (600 US)
4 times each day
0000, 0600, 1200, 1800 GMT
Weather Observations
Data is collected and
formatted in
accordance with the
Marine Observer’s
Handbook.
http://www.nws.noaa.gov/om
/marine/handbk1.pdf
Weather Instruments
Aneroid Barometer
Measures 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 Barometer
Must 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 Instruments
Barograph
A recording
barometer.
Weather Instruments
Thermometer
Measures air
temperature.
You must be able to
convert between
Celsius and
Fahrenheit scales.
Temperature Conversions
Temperature Conversions
Weather Instruments
Hygrometer
Measures Relative Humidity and
Dew Point.
Weather Instruments
Relative 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 Instruments
Hygrometer
Most common type: sling
psychrometer.
Sling Psychrometer
Two Thermometers: 1 wet, 1 dry
Temperature difference is noted.
Sling Psychrometer
Psychrometer
Weather Instruments
Wind Vane
Measures apparent wind direction.
Anemometer
Measures apparent wind speed.
Weather Instruments
Wind Vane
Anemometer
Wind
Definitions
True wind. The speed and direction from which
the wind blows with reference to a fixed point.
Apparent wind. The speed and direction (true
or relative) from which the wind appears to blow
with reference to a moving point.
Wind
Examples
True wind: East wind, 10 knots.
Ship: course 090° T, speed 5 knots.
Apparent wind: From 090° T (000° R), 15 knots.
Wind
Examples
True wind: West wind, 10 knots.
Ship: course 090° T, speed 5 knots.
Apparent wind: 270° T (180° R), 5 knots.
Wind
Anemometers 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.
Wind
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. What is the true wind?
Wind
Step 1: Plot ship’s course
& speed.
Wind
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.
Step 2: Convert relative direction of
apparent wind to true direction, if
necessary.
R+S=T
040° R + 240° = 280° T
Step 3: Draw the apparent wind from the tip of the
Wind
ship’s course
& speed vector.
(Remember, draw the direction the wind is blowing
towards!)
Step 4: Complete the triangle. Result = True wind.
Wind
Direction = 315 °T
Speed = 20 knots
Wind Measurement
Beaufort Scale
If 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 Navigation
Questions?