In today’s increasing use of electronic navigation aids, the ability to correct and un-correct a compass heading or bearing seems to becoming a lost art outside of a classroom. Here are a few TVMDC Practice Problems to help keep your navigation skills sharp.
“Correcting” is converting a magnetic (M) direction to true (T). “Un-correcting” is converting from true to a magnetic direction. “True” direction is relative to true north (north pole).
Deviation is the failure of the compass to point to magnetic north. Deviation is caused by local magnetic fields on the boat. These fields may be caused by the engine, instruments or other electronic equipment, power wiring, tools or any other magnetic objects. Deviation is specific to an individual boat. Deviation changes with the boats heading. Deviation is read from the Deviation Table on the boat.
Variation is the failure of the compass to point to true north. Variation is read from the compass rose on the chart. Variation is the same for all boats in the same area. Variation is the same for all directions in the same area.
I always use the same order for the formula working the solution either up or down, this always puts the same information in the same order, this makes checking the work easier and makes is easy for someone to double check the calculations. DON’T ever just do the good old piece of scratch paper where you just add one number to another, that seems to produce much higher rates of errors.
↓ T ↑ True (-) E ↓ V ↑ (-) W Variation ↓ M ↑ Magnetic (+) W ↓ D ↑ (+) E Deviation ↓ C ↑ Compass Tele-Vision Makes Dull Children add Wonder. The heading must be uncorrected to provide a compass reading for the helmsman to steer.
Piloting and Navigators Quick Reference – Reference card with help for correcting and uncorrecting a compass, speed / time formulas and other quick hints for navigators.
More TVMDC – Practice Problems – Correcting and un-correcting the compass – More TVMDC Practice Problems and TVMDC help.
Correcting Compass Error – More TVMDC Practice Problems and TVMDC help.
TVMDC Practice Problems
TVMDC Practice Problem – Answers
Thanks to Captain’s Nautical in Seattle for letting me use one of their compass’s and letting me spread a chart out in the middle of their store on the floor while I took the picture for the header.
Thanks for your interest in and support of boating safety
c / m