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• Tidal theories


  The application of continuum mechanics to interpret and predict the tidal deformations of planetary and satellite bodies and their atmospheres and oceans (especially Earth's oceans) under the gravitational loading of another astronomical body or bodies (especially the Moon and Sun)
• Tides


  • The rise and fall of sea levels caused by the gravitational pull of the Moon and the Sun on the Earth's oceans
  • They are complex and can be influenced by a variety of factors, including the shape of the sea floor, the position of the Moon and the Sun, and the rotation of the Earth
• Inundation


  Overwhelming abundance
• Gravity


  The force that attracts a body towards the center of the Earth or towards a physical body having a mass
• Spring tides


  1. Occur during new and full moon

  2. Popularly known as a "King Tide"—refers to the 'springing forth' of the tide
• Neap tides


  1. Occur seven days after a spring tide

  2. Refer to a period of moderate tides when the sun and moon are at right angles to each other
• Types of tides


  • Diurnal - occur once a day
  • Semidiurnal - occur twice a day
  • Mixed - are a combination of both diurnal and semidiurnal tides
  • Macro - are exceptionally high tides that occur due to specific geographical features
• Macro tides


  • Have a tidal range—the difference between high tide and low tide—that is higher than 4 meters (13 feet and 1½ inches)
  • Unlike regular tides, they can be influenced by factors such as coastal shape, underwater topography, and local currents
  • They play a significant role in shaping coastal ecosystems and can impact erosion, sediment transport, and marine
• Tidal cycle


  The rise and fall of the sea level that lasts for approximately 24 hours and 50 minutes
• Slack tide


  A period of approximately 30 minutes when the tide is neither incoming nor outgoing, and the water is relatively still
• Cotidal line


  A line on a map connecting points at which a tidal level, especially high tide, occurs simultaneously
• Lunar day


  The time it takes for the moon to orbit the Earth, which is approximately 24 hours and 50 minutes
• When the sun and the moon are aligned


  Their combined gravitational forces create higher tides, known as spring tides
• When the sun and the moon are at right angles to each other


  Their gravitational forces partially cancel each other out, resulting in lower tides, known as neap tides
• Four stages in the tidal cycle

  1. Water stops falling, reaching a local minimum called low tide

  2. Sea level rises over several hours, covering the intertidal zone; flood tide

  3. The water stops rising, reaching a local maximum called high tide

  4. Sea level falls over several hours, revealing the intertidal zone; ebb tide
• Intertidal zone


  The region of land below water at high tides and above water at low tides
• Tidal amplitude


  The difference in height between high tide and low tide
• Gravitational forces


  Forces exerted by the Moon and Sun on Earth
• Centrifugal force


  A force that arises due to Earth's movement around the Earth-Moon barycenter (center of mass of two moving bodies)
• Chart datum


  The level of water that charted depths displayed on a nautical chart are measured from, generally a tidal datum derived from some phase of the tide
• Lowest astronomical tide (LAT)


  The lowest level of water that can be predicted to occur under average meteorological conditions
• Mean lower low water (MLLW)


  The average height of the lowest tide recorded at a tide station each day during the recording period
• Drying height


  An area that is above the chart datum, but does not necessarily mean it will dry out
• Observed depth


  The amount of water you expect to find, calculated by combining the height of tide with the charted depth
• Tide tables


  Used for tidal prediction, showing the daily times and levels of high and low tides for a particular location
• Tidal diamond


  Indicates the direction and speed of tidal stream
• Horizontal datum


  Must not be confused with the vertical datum for the chart
• Meteorological effects


  Such as high pressure systems, can cause lower tides than predicted
• Mean high water spring (MHWS)


  A different vertical datum that some height values on charts may be referenced to
• Highest astronomical tide (HAT)


  A different vertical datum that some height values on charts may be referenced to
• To calculate the tidal range

  1. Determine the high tide level (HT) in meters

  2. Determine the low tide level (LT) in meters

  3. Use the formula: Tidal Range (TR) = HT - LT
• Admiralty Tide Tables


  Detail the times and heights of high and low waters for over 230 standard and 6000 secondary ports
• Tidal analysis


  Provides the basis for predicting tides at future times, and can be interpreted scientifically in terms of the hydrodynamics of the seas and their responses to tidal forcing
• Notices to Mariners (NtM)

  Corrections to nautical charts and publications that contain information vital to safety at sea
• Temporary and Preliminary Notices (T&P)


  Provided in Weekly Notices to Mariners to inform the mariner of any temporary or preliminary navigation-affecting changes
• Failure to keep charts up to date is in contravention of SOLAS and puts the ship, the owner and seafarers in danger
• Equipment for chart/publication correction

  • Parallel ruler
  • Triangles
  • Compass divider
  • Drawing materials
  • Correction pen
  • Pencil
• New Chart


  Published by the Admiralty when a new area is to be added to a chart, the depth units or scale have to be changed, or the area represented is different from the previous chart
• New Edition


  Published by the Admiralty when there are major changes in a chart or a large amount of new data is to be inserted, replacing the existing chart
• It is essential that masters and any persons responsible for the upkeep of charts are aware of the procedure for collating the information from all notices to mariners and ensuring that all applicable notices are applied to the charts in use