Mike’s weekly quiz…Week 1

  • This topic has 4 replies, 4 voices, and was last updated 2 months ago by Sarah Cummins.
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  • #18958
    Mike Gilbert
    Participant

    Hi everyone,

    During this time of Covid and the difficulties it poses with us getting together I thought it might be fun to throw some questions out that might just need some research to find the correct answer(s), be thought provoking (ie. no real answers – just personal preference), or requires some calculations to come up with the correct answer(s).  Looking to throw a quiz out once a week until the end of April.  If this is not appropriate to do on the Forum let me know.  Participate if you like.  Share answers as you like.  Have fun with it.  Maybe gain a bit more knowledge?

    Quiz 1 – Topic of Navigation (seeing as we are all trying to find our right direction during this time!)

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

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

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

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

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

Viewing 4 replies - 1 through 4 (of 4 total)
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  • #18985
    Sarah Cummins

    Hi everyone. Love this quiz thing . Here is my attempt to answer , written before I read Martins answers which are really good !
    1) True North  determined by axis of rotation of earth
    Grid North determined by grid lines on map or chart a pressed on flat surface rather than actual curvature of surface of earth.
    Magnetic North shown by compass which points towards North as determined by earth’s own magnetic field . Dynamic and varies from year to year.

    2) Variation = the difference between True North and Magnetic North on water .
    Declination = difference between True North and Magnetic North on land .
    Deviation = an error in a compass reading caused by the influence of the magnetic field of nearby object .

    3) marine MC and orienteering compass OC

    MC used to know which direction the boat is pointed ( but not necessarily the direction of travel !)  OC used to take bearings and orient map to terrain

    MC readings taken on fixed lubber line painted in direction of head of vessel .
    OC readings taken using fixed site and spinning dial .

    MC mounted on deck of boat , aligned to centre line of boat .
    OC hand held and can be mounted to base plate used as protractor .

    MC is not used to make chart or map measurements OC used to make chart and map measurements

    MC indicates magnetic North .
    OC can determine magnetic North and true north

    4) Bearing  = compass direction to landmark .
    Heading=direction kayak is pointing but not necessarily moving towards depending on wind current .
    Course = route actually plotted /followed , distance and direction over water

    5).   Variable  from year to year. Currently @ 16 degrees east declination  and 23 degrees east variation .

    thanks for posting. Looking forward to more quizzes !  Sz

    #18979
    Yekaterina Yushmanova

    How fun! Thanks, Mike!

    #18970
    Mike Gilbert

    Well done, Martin.

    Next week we will tackle some questions to do with Tides and Currents.

    #18966
    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 https://www.geomag.nrcan.gc.ca/calc/mdcal-en.php
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