Reply To: Mike’s weekly quiz…Week 1

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