Meteorology and Communications for Safe Navigation

Posted on May 1, 2024 in Other subjects

Meteorology

5.1 Importance of Time, Barometer

Weather directly affects wind and sea conditions, impacting vessel safety. Gathering weather information before sailing is crucial.

Atmospheric Pressure

Definition: Weight of air above Earth due to gravity.

Measurement: Millimeters (mm), inches, or millibars (mb).

Sea Level Pressure: 760 mm = 1013.2 mb = 1 atmosphere.

Barometer

Instrument for measuring atmospheric pressure. Types:

  • Mercury (not used in sailing)
  • Aneroid (uses expansion/contraction of tubes or capsules)

Aneroid Barometer

Measures pressure using a capsule and indicates it on a scale (mm, inches, or mb).

Conversions:

  • 1 mm = 1.33 mb = 0.039″
  • 1 mb = 0.75 mm = 0.029″
  • 1″ = 25.4 mm = 33.86 mb

Barograph

Aneroid barometer with a pen that records pressure variations on a rotating cylinder.

5.2 Isobaric Lines, Depressions, and Anticyclones

Isobaric Lines: Lines on weather maps connecting points with the same atmospheric pressure (spaced 4 mb apart).

Depressions (Lows)

Centers of low pressure, often associated with cloudiness and precipitation.

Anticyclones (Highs)

Centers of high pressure, can be fixed or mobile. Fixed ones favor fog formation.

Wind Circulation (Northern Hemisphere)

  • Cyclone: Clockwise and outward
  • Anticyclone: Counterclockwise and inward

Buys Ballot’s Law

Facing the wind, low pressure is located between 90º and 135º clockwise (Northern Hemisphere).

Tracks of Storms

Generally move from west to east in the Northern Hemisphere.

5.3 Wind

Moving air caused by pressure differences due to temperature variations.

Wind Direction

Indicated by where the wind is coming from.

True Wind

Wind felt when the ship is stationary.

Apparent Wind

Wind felt when the ship is moving, a combination of true wind and boat speed.

Wind Terminology

  • Veer: Change in wind direction.
  • Back: Sudden change to the opposite direction.
  • Ease: Decrease in wind strength.
  • Freshen: Increase in wind strength.
  • Gust: Brief, intense increase in wind speed.
  • Squall: Sudden change in wind speed and direction.
  • Lull: Decrease in wind or sea force.

5.4 Coastal Breezes

Weak local winds caused by temperature differences between land and sea.

Land Breeze (Offshore)

Occurs at night when cooler air from land moves towards the warmer sea.

Sea Breeze (Onshore)

Occurs during the day when cooler air from the sea moves towards the warmer land.

5.5 Measurement of Wind

Beaufort Scale

Measures wind force based on observed sea conditions (0-12).

Anemometer

Measures wind speed (apparent wind).

Wind Vane

Indicates wind direction.

5.6 Sea State

Douglas Sea Scale

Measures sea state based on wave height (0-9).

Factors Affecting Sea State

  • Intensity: Wind strength.
  • Persistence: Duration of wind in the same direction and intensity.
  • Fetch: Area over which the wind blows in the same direction and intensity.

5.7 Temperature

State of heat in the atmosphere.

Isotherms

Lines connecting points with the same temperature.

Thermometer

Measures temperature using various physical properties (e.g., liquid expansion).

Temperature Scales

  • Celsius (°C): 0°C (freezing), 100°C (boiling)
  • Fahrenheit (°F): Conversion formulas: C° = (F° – 32) * (5/9), F° = (C° * (9/5)) + 32

5.8 Weather Information

Weather Reports

National Meteorological Institute provides short-term reports for coastal areas.

Sources

  • VHF radio
  • Teletiempo sea (phone service)
  • Internet
  • Nautical clubs and marinas

Storm Warnings

Broadcast on VHF channel 16.

Barometer and Thermometer Observations

Can provide general weather trends:

  • Rising pressure, falling temperature: Improving conditions.
  • Falling pressure, rising temperature: Worsening conditions.

Squalls

Short-term weather events with sudden changes in wind, rain, etc.

Cloud Observations

Can provide clues about upcoming weather changes.

Communications

6.1 Definitions

Telecommunications: Transmission/reception of signals using various systems.

Radio: Communication using radio waves.

Radio Waves: Electromagnetic waves with frequencies less than 3,000 GHz.

Radiotelephone: Device for radio communication.

Station: Transmitters/receivers for radiocommunication service.

Ship Station: Radio station on a ship.

Coast Station: Land-based station for maritime communication.

Maritime Mobile Service: Communication between ship and coast stations.

VHF: Frequencies between 30 and 300 MHz, commonly used on recreational boats.

Channel: Specific frequency for communication.

Simplex: One station transmits at a time.

Duplex: Stations transmit and receive simultaneously.

Half-duplex: Combination of simplex and duplex.

6.2 Discipline in Radio Use

Prohibited transmissions:

  • Useless transmissions
  • Unidentified or false identification
  • Transmissions not directed at a specific station
  • Transmissions within ports and roads (except distress, urgency, safety)

Minimize transmission power.

6.3 Communication Procedure

Calling and Working Channels

  • Ship-to-ship: Channel 16 (156.80 MHz) for calling, any unused channel for working.
  • Ship-to-coast: Channel 16 (156.80 MHz) for calling, assigned working channel.
  • Yacht clubs: VHF channel 9.

General Procedure

Calling:

  1. Call sign of called station (3 times)
  2. “Here”
  3. Call sign of calling station (3 times)

Repeating the Call:

  • Repeat 3 times with 2-minute intervals, then suspend.
  • If no response, repeat at 3-minute intervals.

Reception:

  1. Call sign of calling station (up to 3 times)
  2. “Here”
  3. Call sign of receiving station (up to 3 times)
  4. Switch to working channel

Conversation:

  • On working channel
  • Alternate transmissions, ending with “Over and Out”

Termination:

  • Indicate with “Done”

6.4 Distress, Urgency, and Safety

General

  • Broadcast to all listeners.
  • Use phonetic alphabet if needed.
  • Only with permission of the skipper.
  • Communicate when danger is over.
  • Priority over other calls.

Distress Message

Cause: Grave and imminent danger, requiring immediate assistance.

Signal: Two-tone alarm (30-60 seconds).

Call: MAYDAY MAYDAY MAYDAY

Message:

  • Location
  • Nature of distress and assistance required
  • Other relevant information

Urgency Message

Cause: Urgent message concerning safety.

Call: PAN PAN PAN

Safety Message

Cause: Important message for navigation safety.

Call: SECURITE SECURITE SECURITE

Emergency Telephone

900 202 202 (Spain)

Radio Silence Periods

3 minutes after the hour and half-hour.

6.5 Special Services

  • Radio medical advice
  • Notices to Mariners (navigation warnings)
  • Weather reports
  • Radio conferences

6.6 Obligations

  • VHF radio required in navigation area “C”.
  • Equipment must be approved.