Earth's Shape: Nearly a spheroid, with the axis shorter by 43 km than the equatorial diameter (approximately 13,000 km for calculation).
Axis: An imaginary straight line around which the Earth rotates daily; points where it intersects the surface are the geographic poles (North and South).
Equatorial Plane: Perpendicular to Earth’s axis, dividing the globe into Northern and Southern Hemispheres; the great circle formed is the equator.
Parallels: Smaller circles parallel to the equator.
Meridians: Lines from pole to pole, perpendicular to the equatorial plane; the prime meridian through Greenwich is the reference for dividing the globe into Eastern and Western Hemispheres.
GEOGRAPHIC COORDINATES
Definition: Specifies location on the Earth using latitude (φ) and longitude (λ).
Latitude (φ): Angle between the equator and a point on the surface; ranges from 0° to 90° (North or South).
Longitude (λ): Angle between the Greenwich meridian and a point's meridian; ranges from 0° to 180° (East or West).
NAVIGATION UNITS OF MEASUREMENT
Nautical Mile: One minute of arc along the meridian; equals 1852 meters.
Knot: Speed of one nautical mile per hour.
DIRECTIONS
Direction Representation: Expressed as a horizontal angle from a starting direction, commonly using true meridian or ship's heading as reference.
Horizontal Division:
Divided into quarters (NE, SE, SW, NW, etc.) that can yield 32 distinct points called strēķi.
Degree Method:
Divides the horizon into 360° for navigation, with angles measured clockwise starting from North.
COURSE AND HEADING
True Course (IK): Angle between the true north and the ship's heading.
True Bearing (IP): Angle between true north and direction to an object.
Heading Line (IKL): Projection of the ship’s direction.
Course Angle (KL): Angle between the ship's heading and direction to an object.
VISIBLE HORIZON
Visible Horizon: Line where the sky appears to meet the water surface; distance dependent on the observer’s eye height.
Beacon Visibility Distance: Distance from which a beacon can be seen based on observer’s height; adjusts for Earth’s curvature.
MAGNETIC VARIATION AND DEVIATION
Earth's Magnetism: Earth has magnetic poles that differ from geographic poles; magnetic variation (d) is the angle between true and magnetic meridian.
Deviation Calculation (∂): Angle formed by the magnetic and compass meridians affected by the vessel's structures.
Compass Correction (AK): The algebraic sum of magnetic variation and deviation.
COURSE TRANSFERRING AND CORRECTION
Course Conversion: Converting between compass direction and true direction using variation and deviation.
Drift Angle (α): Angle formed due to wind’s effect on a ship, calculated varying by the helm (left or right).
SEA CURRENTS
Definition: Movement of water caused by astronomical or meteorological factors, classified into persistent, periodic, and transient.
Elements: Current direction and speed affect the ship’s movement, influencing calculations of true speed (SOG) and course (IK).
Current Triangle: A graphical representation to calculate a course and SOG factoring in drift.
NAVIGATION CHARTS
Chart Requirements: Should show the shortest, safest, and fastest route while representing geographic features accurately.
Mercator Projection: A method to represent the Earth’s curved surface on a flat plane, preserving angles but distorting size.
Classification of Charts:
General Charts: Scale 1:500,000 or smaller.
Voyage Charts: Scale 1:100,000 to 1:150,000.
Regional Charts: Scale 1:25,000 to 1:75,000.
Plans: Large scale, often 1:100 to 1:20,000 for harbors and detailed areas.
POSITION DETERMINATION
Methods: Using bearings from land objects, deduct based on compass corrections to obtain true bearings and position.
Error Triangle: The shape formed when three bearings do not intersect at one point, indicating the observed position.