Reply To: Mike’s weekly quiz…Week 1

Martin Feuchtwanger

1. What is the difference between True North, Grid North and Magnetic North?

  • True North is the direction of the local meridian, to Earth’s North Pole.
  • Grid North is the direction of the up-and-down grid lines on a topographic map, and is only a few minutes or seconds off True North. (On marine charts, Grid and True North are the same.)
  • Magnetic North is the direction of the local magnetic meridian, or magnetic force field, to Earth’s Magnetic Pole, and can be off True North by many degrees.

2. How do you differentiate between Declination, Variation and Deviation?

  • Declination and Variation both refer to the difference between True North and Magnetic North at any location. “Declination” is used on topographic maps and “Variation” is used on marine charts.
  • Deviation refers to the error introduced to a compass needle if/when it detects metal or other magnetic items on the boat that cause it to deviate away from its natural magnetic meridian.

3. List the differences between a marine compass and an orienteering compass.

  • Marine compass (MC) is fixed to the boat and aligned with its centre-line.
    Orienteering compass (OC) is hand-held.
  • MC floats horizontally inside a sphere, allowing it to be read during pitching and tilting of the boat.
    OC must be held horizontally for the needle to move freely.
  • MC is designed such that the cursor always indicates the current magnetic direction of the boat.
    OC will give the current magnetic direction of its base plate only if the dial has been carefully and separately turned to align with the compass needle.
  • MC cannot be used to make map or chart measurements.
    OC can be placed on a map or chart and can measure angles between any two lines.

4. Explain how each of the following is different:  Bearing;  Heading;  Course

  • Bearing is the direction (i.e., clockwise angle from North) to a particular target.
    Bearing depends on the relative positions of boat and target and independent of  their individual orientations.
  • Heading is the present direction (angle from North) of a boat at any given instant.
    Heading depends on where the boat is pointing and is independent of boat position.
  • Course is the direction of the boat’s path of travel, planned or actual.
    Course depends on successive boat positions.
  • Course and Heading will differ when the lateral forces of wind, waves or current cause the boat to move in a direction (Course) away from where it is pointing (Heading).

5. For the west coast of BC what is currently the typical number of degrees of declination (and to which direction) from True North?

  • Declination (or variation) in Vancouver is about 15.5 degrees east of True North (in 2020).
  • In Tofino it is about 16 degrees east.
  • In Telegraph Cove it is about 16.5 degrees east.
  • As Declination changes noticeably year by year, check it via