Nautical Charts Overview

Nautical Charts

• A navigational chart is a representation of an area of navigable water on a flat surface.
• Charts are classified based on scale.
• Small Scale Charts cover a larger area with less detail and are used for offshore and longer trips.
• Large Scale Charts offer more detail and higher resolution, used for coastal planning, and are frequently resurveyed.

Types of Charts

• Sailing Chart (1:1,500,000 or larger) - Used for planning, fixed position at sea, plotting dead reckoning positions in long voyages.
• General Chart (1:350,000 to 1:500,000) - Used for coastal navigation well offshore but with fixed landmarks, lights, buoys, and soundings.
• Coastal Chart (1:75,000 to 1:350,000) - Used for nearshore navigation, entering bays and harbors, and larger inland waterways.
• Approaching Chart (1:25,000 to 1:75,000) - Used to help approach harbors and feature hazards to avoid accidents.
• Harbor Chart (1:5,000 to 1:25,000) - Used for navigating a harbor and maneuvering pier or wharf.
• Berthing Chart (Less than 1:5,000) - Used for maneuvering within a harbor.

Chart Projection

• Chart projection is a transformation of latitudes and longitudes from a curved Earth to a flat surface.
• Types of projections include:
  • Gnomonic Projection - Light source at the center of the globe.
  • Stereographic Projection - Light source at the antipode of the point of tangency.
  • Orthographic Projection - Light source at infinite distance from the point of tangency.
• Factors involved in chart projection include:
  • Geoid - A rendition of the irregular, spheroidal shape of the Earth.
  • Ellipsoid - A regular geometric reference surface used to model the Earth.
  • Projection - Transforming the ellipsoid into a 2-dimensional plane.

Properties of Map Projection

• Conformality - Preserves shapes, with minimal distortion between standard parallels.
• Equidistance - Preserves distances along specific lines.
• Equivalency - Preserves areas.

Commonly Used Map Projections

• Mercator Projection - Uses straight meridians and parallels, measures distance accurately only along the equator.
• Universal Transverse Mercator (UTM) Grid - Divides Earth into 60 zones, each covering six degrees of longitude.
• Lambert Conformal Conic - Projects conformally to a cone placed over the Earth.

Chart Reading

• Colors indicate depths and types of seabed:
  • White represents deep water.
  • Blue represents shallow water, with darker blue indicating less water.
  • Green indicates the foreshore.
  • Yellow Brown indicates the shoreline.
  • Pink represents lighthouses, underwater cables, and restricted areas.
• Capital Letters indicate the type of seabed:
  • S - Sand
  • R - Rock
  • M - Mud
  • Wd - Weed
  • Sh - Shells
  • St - Stones
  • G - Gravel
  • P - Pebbles
  • Bo - Boulders
  • Co - Coral

Chart Correction and Updating

• A systematic process ensures the accuracy of nautical charts.
• Notice to Mariners (NTM) provides timely information for correcting and updating charts.

WGS84 Datum

• Comprehensive geodetic reference system for global positioning and navigation technologies.
• Comprises of four elements:
  • Ellipsoid Datum - Defines a reference ellipsoid to model the Earth.
  • Horizontal Datum - Used for plotting geographical locations on charts.
  • Vertical Datum - Defines elevations and depths.
  • Coordinate System - Based on longitude and latitude.

Nautical Publications

• Sailing Directions - Detailed information on harbors, ports, navigational hazards, local information, and pilotage requirements.

World Port Index (PUB 150)

• A tabular listing of ports, including location, characteristics, facilities, and available services.

This quiz explores the different types of nautical charts and their classifications based on scale. Understand the use of small and large scale charts in navigating coastal and offshore waters. Test your knowledge on specific chart types used for various navigation tasks.