TVMDC – Practice – Correcting and un-correcting the compass

TVMDC – Practice – Correcting and un-correcting the compassIn 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 – 48 More TVMDC Practice Problems and TVMDC help.

Correcting Compass Error – More TVMDC Practice Problems and TVMDC help.

TVMDC Practice Problems

01 02 03 04 05 06
T 343 002 091 004
V 005E 017W 003E 047E
M 322 200 226 352
D 003E 007W 007W
C 202 083 354
07 08 09 10 11 12
T 193 353 004
V 017W 023E 012W 012E 021E 014W
M 005
D 003E 005W 006E 003E 006E
C 019 112 345
13 14 15 16 17 18
T 343 183
V 007W 017E 003W 014W 018W
M 004 009 094
D 005E 006E 003W 002W
C 001 161 008 178
19 20 21 22 23 24
T 015 079 083
V 018W 012W 023E 012E 003E
M 038 189
D 004E 004E 002W
C 100 088 195 157 355

TVMDC Practice Problem – Answers

01 02 03 04 05 06
T 343 002 183 091 273 004
V 021E 005E 017W 003E 047E 012E
M 322 357 200 088 226 352
D 003E 007W 002W 005E 007W 002W
C 319 004 202 083 233 354
07 08 09 10 11 12
T 193 037 353 127 004 351
V 017W 023E 012W 012E 021E 014W
M 210 014 005 115 343 005
D 003E 005W 006E 003E 002W 006E
C 207 019 359 112 345 359
13 14 15 16 17 18
T 343 002 183 091 351 158
V 021W 007W 017E 003W 014W 018W
M 004 009 166 094 005 176
D 003E 005E 005E 006E 003W 002W
C 001 004 161 088 008 178
19 20 21 22 23 24
T 015 079 083 212 173 356
V 023W 018W 012W 023E 012E 003E
M 038 097 095 189 161 353
D 004E 003W 007E 006W 004E 002W
C 034 100 088 195 157 355

Printer Friendly TVMDC practice sheets (pdf).

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

This entry was posted in Boating Safety, Navigation, Safety Thoughts, Sailing and Boating Skills and tagged , , , , , . Bookmark the permalink.

13 Responses to TVMDC – Practice – Correcting and un-correcting the compass

  1. Bill Haimes says:

    The simpler method is to keep the gps in magnetic, Have the steering compass properly adjusted and do all plotting from the magnetic rose. True is only a problem when using a gyro. You will not be able to develop a deviation table for the hand bearing compass since it is portable. A properly adjusted steering compass should have residual deviation of less than two degrees on any heading, well within the steering accuracy of most helmsmen.

  2. venjie paya says:

    sir can you gave me a easier method on how to solve variation and deviation error?

    • captnmike says:

      There are some links in the original Post that should help a bit – I have a copy of the Nav. Quick Reference that I keep with me as a double check. I also always write things down in the same order – no shortcuts – the only other advice is to work a ton of problems – they get easier after a while

      • A says:

        I agree with captain mike – look at the answers he provided and do the math, you’ll pick up the pattern. I’m taking the oupv online course and it did a horrendous job of explaining everything. Thanks a lot captain mike, i’m printing off your cheat sheet as well. Very helpful indeed.

      • captnmike says:

        Glad you found this helpful – I have given many copies of the cheat sheet Navigators Quick Reference to people

  3. God day sir !..,i want to clarify in the PROBLEM column 02, is the Magnetic becomes 357 or it is 003 either? and Compass was 004 or it is 010?
    Thanks a lot Captain Mike, your links is awesome.
    Very helpful indeed.

    God bless. :)

    • captnmike says:

      Coll #2 – the answers are 357M & 004C

      (002T + 360 = 362) – (005E) = 357M

      357M + 007W = 364 ( 364 – 360 = 004C) = 004C passed to the helm to steer

  4. Anonymous says:

    T-002
    V-005
    M-357 WHY THESE IS THE ANSWER?
    D-007
    C-004

    • captnmike says:

      When you are moving from True to Magnetic (see the formula at the top of the page) you SUBTRACT EAST – since the True is 002T and we are going through 000 / 360.

      We need to make the math work so 360 + 002T = 362T

      then Subtract 005E – 362 = 357M

      Hope this helps.

      You might find this card useful Piloting and Navigators Quick Reference Print it out on heavy paper of contrasting color.

  5. WHY 357 IS THE ANSWER TO THE LETTER M?

  6. Gising Tulog says:

    sir can u give me some hints to solve tides

    • captnmike says:

      You can use the Rule of 12 to roughly show the change in the water level between high & low tide –

      Take the time between high & low (or low & high) tide times. The time between is divided into 6 intervals – the first interval the water level changes 1/12 of total, – 2nd interval 2/12 of total, 3rd interval 3/12 of total, 4th interval 3/12 of total, 5th interval 2/12th of total, 6th interval 1/12 of total.

      I remember it by 1,2,3,3,2,1, – bit tough to show this without a sketch – I hope this helps a bit

      Thanks for visiting

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