# Magnetic compass to true course **URL:** \ **Category:** Professional Mariner Forum\ **Created:** [October 11, 2011, 1:59pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312 "2011-10-11T13:59:27Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Jemplayer](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.gcaptain.com/jemplayer/32/523_2.png) [@Jemplayer](https://forum.gcaptain.com/u/Jemplayer)\ **Post date:** [October 12, 2011, 4:01pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/21 "2011-10-12T16:01:19Z")
Convert everything to true as your going to use the compass rose on the chart. Also do not use the magnetic variation on the chart, use the variation stated in the question. ---
**Author:** ![Tugboattim](https://avatars.discourse-cdn.com/v4/letter/t/4bbf92/32.png) [@Tugboattim](https://forum.gcaptain.com/u/Tugboattim)\ **Post date:** [October 12, 2011, 4:19pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/22 "2011-10-12T16:19:33Z")
The correct answer is C (I looked it up on Capt. Joes) I dont have the chart in front of me so i cant say my work is correct. but try this: Plot these as True on the Chart Brandford - 008\* New Haven - 281\* Tweed airport - 319\* ill show you my calculations if it works, i wouldnt wanna mess you up if its wrong. ---
**Author:** ![seadawg](https://avatars.discourse-cdn.com/v4/letter/s/3da27b/32.png) [@seadawg](https://forum.gcaptain.com/u/seadawg)\ **Post date:** [October 12, 2011, 4:22pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/23 "2011-10-12T16:22:08Z")
[QUOTE=xavierts29;56355]Heres The Whole Question And the heading at the top of the test. #1 - USCG 16306 The following questions are based on chart 12354TR, Long Island Sound - Eastern Part, and the supporting publications. Your vessel has a draft of 10 feet (3.1 meters). Your height of eye is 35 feet (10.6 meters). Use 14° W variation where required. The deviation table is: HDG. MAG. DEV. HDG. MAG. DEV. HDG. MAG. DEV. 000° 0° 120° 2° W 240° 3° E 030° 1° W 150° 1° W 270° 3° E 060° 2° W 180° 1° E 300° 2° E 090° 4° W 210° 2° E 330° 1° E #10 - USCG 16315 At 0820, you change course to 301° psc and reduce speed to 7.5 knots. At 0900, you take the following visual bearings: Branford Reef Light 023° psc New Haven Light 293° psc Tweed Airport Aerobeacon 332° psc Your 0900 position is \_\_\_\_\_\_\_\_\_\_. See Diagram: D16315NP A. LAT 41° 11.9’ N, LONG 72° 50.6’ W B. LAT 41° 11.9’ N, LONG 72° 49.5’ W C. LAT 41° 12.1’ N, LONG 72° 48.6’ W D. LAT 41° 12.5’ N, LONG 72° 44.3’ W Now Heres the thing I would like to know do you need to convert that to true? If so How? If not What is the way you plot it out as is?[/QUOTE] plot true courses… C (psc) 301\* D 3_E M 303_ V 14_W T 289_ your question indicates a lack of the basic rudimentary concepts of navigation…in order to succeed working plot problems you will need to be able to work compass, add/subtract time, and time/distance/speed problems as second nature…suggest enrolling in a course ASAP! ---
**Author:** ![Diesel](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Diesel](https://forum.gcaptain.com/u/Diesel)\ **Post date:** [October 12, 2011, 4:31pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/24 "2011-10-12T16:31:42Z")
The situation is exactly as I stated earlier…he has the deviation table right there. He needs to learn to derive his deviation from that based on the course he is on, and Jemplayer is right on…magnetic schmagmetic there is no CG question that I am aware of that has you use just the magnetic course portion of the conversion. It will always be PSC and you will always need deviation. Xavierts as much as I would like to help you it is impossible to teach this through the forum. Best advice I can give is look up a deviation table problem and learn how to do them from the solution, that will be your next step. What you are trying to do is like going from driving a big wheel to an Indy Car. You are skipping a few prerequisites and it is confusing you. You are capable but you need to take a few steps back and learn some of the basics. Hope this helps bro. After you learn deviation tables this is how you attack this one. Convert all the bearing to true, plot the LOP’s and get your 0900 fix. Remember the deviation to use is based on your ship’s heading not on the objects bearing PSC. In other words the deviation will be the same for all three LOP conversions. Little more help, in this case it looks like your deviation is 2 degrees E, hard to tell 100% because the columns are not lined up. [QUOTE=xavierts29;56355]Heres The Whole Question And the heading at the top of the test. #1 - USCG 16306 The following questions are based on chart 12354TR, Long Island Sound - Eastern Part, and the supporting publications. Your vessel has a draft of 10 feet (3.1 meters). Your height of eye is 35 feet (10.6 meters). Use 14° W variation where required. The deviation table is: HDG. MAG. DEV. HDG. MAG. DEV. HDG. MAG. DEV. 000° 0° 120° 2° W 240° 3° E 030° 1° W 150° 1° W 270° 3° E 060° 2° W 180° 1° E 300° 2° E 090° 4° W 210° 2° E 330° 1° E #10 - USCG 16315 At 0820, you change course to 301° psc and reduce speed to 7.5 knots. At 0900, you take the following visual bearings: Branford Reef Light 023° psc New Haven Light 293° psc Tweed Airport Aerobeacon 332° psc Your 0900 position is \_\_\_\_\_\_\_\_\_\_. See Diagram: D16315NP A. LAT 41° 11.9’ N, LONG 72° 50.6’ W B. LAT 41° 11.9’ N, LONG 72° 49.5’ W C. LAT 41° 12.1’ N, LONG 72° 48.6’ W D. LAT 41° 12.5’ N, LONG 72° 44.3’ W Now Heres the thing I would like to know do you need to convert that to true? If so How? If not What is the way you plot it out as is?[/QUOTE] ---
**Author:** ![cappy208](https://avatars.discourse-cdn.com/v4/letter/c/7cd45c/32.png) [@cappy208](https://forum.gcaptain.com/u/cappy208)\ **Post date:** [October 12, 2011, 4:35pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/25 "2011-10-12T16:35:19Z")
Zavierts. You are aware of TVMDC ADD EAST correct? ---
**Author:** ![seadawg](https://avatars.discourse-cdn.com/v4/letter/s/3da27b/32.png) [@seadawg](https://forum.gcaptain.com/u/seadawg)\ **Post date:** [October 12, 2011, 4:39pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/26 "2011-10-12T16:39:42Z")
my D should have been the listed 2\*E…sorry for the typeO!! WTF??unable to edit my post?? ---
**Author:** ![Diesel](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Diesel](https://forum.gcaptain.com/u/Diesel)\ **Post date:** [October 12, 2011, 4:55pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/27 "2011-10-12T16:55:06Z")
[QUOTE=cappy208;56368]Zavierts. You are aware of TVMDC ADD EAST correct?[/QUOTE] TVMDC: left to right is add west Gyro error: left to right is add east ---
**Author:** ![seadawg](https://avatars.discourse-cdn.com/v4/letter/s/3da27b/32.png) [@seadawg](https://forum.gcaptain.com/u/seadawg)\ **Post date:** [October 12, 2011, 4:55pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/28 "2011-10-12T16:55:28Z")
to “correct” add EAST/subtract WEST (C\>D\>M\>V\>T) to “uncorrect” subtract EAST/add WEST (T\>V\>M\>D\>C) ---
**Author:** ![cappy208](https://avatars.discourse-cdn.com/v4/letter/c/7cd45c/32.png) [@cappy208](https://forum.gcaptain.com/u/cappy208)\ **Post date:** [October 12, 2011, 6:00pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/29 "2011-10-12T18:00:08Z")
Correct. I worded it wrong, but it appears there,may need more schooling than is possible through tap and type via this forum. ---
**Author:** ![Jeffrox](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@Jeffrox](https://forum.gcaptain.com/u/Jeffrox)\ **Post date:** [October 12, 2011, 8:02pm UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/30 "2011-10-12T20:02:41Z")
True Virgins Make Dull Companions At Weddings TVMDCAddWest Can Dead Men Vote Twice At Elections CDMVTAddEast ---
**Author:** ![Cal](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@Cal](https://forum.gcaptain.com/u/Cal)\ **Post date:** [October 13, 2011, 5:11am UTC](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312/31 "2011-10-13T05:11:52Z")
[QUOTE=xavierts29;56355]Now Heres the thing I would like to know do you need to convert that to true?[/QUOTE] For any USCG question, if you have to actually plot it on a chart, everything must be in True. If you started in PSC, had to plot it on the chart, then give your answer in PSC, you would have to convert to true, make the plot, then convert from true back to PSC. If you don’t your answer will be wrong. Basically, if it goes on the chart, convert it to true. Seadawg answered the question for you and highlighted the important parts but didn’t expand on one part where you are apparently confused. You state that you aren’t given Deviation, which is technically true. However, you are given the means to determine the Deviation, that’s what the Deviation Table is for. For this particular question it’s easy. From the table Deviation on a heading of 300\* is 2_E, 301_ is so close as to be considered the same, no further work necessary. However, if your heading was 315\* PSC then you would need to split the difference between 300\* at 2_E and 330_ at 1_E. So Deviation on a heading of 315_ PSC would be 1.5\*E. [Previous page](https://forum.gcaptain.com/t/magnetic-compass-to-true-course/6312.md?page=1)