On a 200 degree course, per ships compus. With a deviation of 3'W and the Variation is 14'W. You would do the following. Remember when going down the table add West, when going up add east.

T183 - Is the course made good.
V14W = Subtract because West and going up)
M197 = (200 - 3)
D3W =(Subract because West and going up)
C200 = Ships Compus course

 

To check deviation correctly you need to have your boat's bow facing True North. You then may apply the variation and check the difference between the magnetic heading and the compass heading. The result is your deviation. This is a very difficult procedure to do on the water. Regarding "course made good" that is your actual track over the ground which is affected by set and drift. At least that's my undertsanding of it. Good luck.

 

Always remember, True Virgins Make Dull Companions

 

UNLESS YOUR THE ONE.

 

Actually Deviation is the effect of the ships enviroment on the ships compass. Ex. electronics, magnetics, and/or metal objects all effect a magnetic compass. Variation is the difference in true North between the years in is reflected on the charts compass rose.

"True Virgins Make Dull Company add Whiskey to get um going down" is what I use.

Coarse made good is your True heading form A to B on the chart.

Guess I am learning somehting in Captains School.

I see you found the answer. Good stuff.

[ 05-01-2006, 03:07 PM: Message edited by: bear 13 ]

 

Bear.
"Add Whiskey to get um going down"

That means I always add West when going down the problem. right?


ie...

T 217
v 14w
m 231
d 2E As per Boat devation chart for course heading
c 229


MakoMan Thanks your Explanation Gave me a very clear understanding of it and how to check it in the real world.

[ 05-01-2006, 03:38 PM: Message edited by: FreezOrBurn ]

 

Yes sir, you add West when going down the problem. Add East when going up. Hope this helps.

 

west is best (+) east is least (-)

 

In order to make a deviation table, you need to calculate bearings on fixed objects from a chart. The process is known as "swinging your compass". (Do a Google search on that term if you want if the following doesn't make sense.) You then need to take bearings on these objects with your vessel and compare them to the headings given by your compass. Remember that your deviation will vary with the direction the vessel is pointed due to varying magnetic influences aboard your vessel. Thus, your deviation table will have deviations for different headings. Unless you have a severe case of magnetic interfence aboard your vessel, 4 headings should be sufficient, approx. north, south, east and west.

So, on a nautical chart, identify features on the chart of fixed position (towers, fixed buoys, etc.). You will need 2 pairs of items that allow you to run 2 perpendicular courses to calculate the deviation based on various headings as described above. For example, you need to find objects that run in an approx. north/south line with each other and another pair that run approx. east/west.

Now, on the chart, calculate the bearings between the objects. Ideally, you could find objects with bearings of 0/180 and 90/270, but good luck finding them. Calculate the bearings in magnetic degrees (either by plotting magnetic on the chart or plotting true and converting to magnetic using variation as described above).

Next, it's time for your on the water work. Table is best constructed on a day with minimal tidal/wind influences on your vessel. Head out on the water and pick a pair of your objects. Align them like you would a range. (Or line one up on your stern, and head towards the other object, but this will be less accurate.) You have plotted what the magnetic course *should* be, now compare that to what your compass says. (For example, your plotting says from object 1 to object 2 should be 22 deg. magnetic, but your compass says you are heading 25 degrees. Therefore, your variation is 3 degrees west.) Now swing the vessel and head the opposite direction using your range/objects to maintain course. (Course should be 202 degrees but you are steering 200, so deviation is now 2 degrees east when steering in that direction.)

Repeat with your second pair of objects.

Who says all that plotting was for naught on your exams...

[ 05-01-2006, 04:44 PM: Message edited by: captadamnj ]

 

Man....too much "captains course" stuff in here....you are doing it the hard way....

Just go out on a light wind day...in a large body of water with little or no current...set your GPS to magnetic and calibrate your compass to the CMG. (it IS the M in TVMDC) as long as your head looks good to your CMG (it should be on a windless, current less day). Do it on at least the 4 primary headings and I usually do it on the 45's if I can.

The new compass instructions are now telling you to do it this way and there is no reason why you can't. You can get even the smallest of compasses to withing 5 degrees or so on most of the headings...then construct a deviation table to that....getting better than that or needing better accuracy on the small compasses would be an excercise in futility for the most part as the markings on the compass are often in 5 degree graduations anyway....

[ 05-01-2006, 07:07 PM: Message edited by: Capt. Scott ]

 

I am still not totally in agreement with the way they teach the subject in captain's school. In the Navy, we used the following as a "gouge" to compute headings "Can Dead Men Vote Twice At Elections". Interpreted, it is Compass, Deviation, Magnetic, Variation, True, Add East to Magnetic to get true. Maybe it's because I used it for 30 years, but it seems like an easier formula to use. Whatever works!!!!!!

 

Scott, The calibrating compass issue has got me puzzled for the last year.

My compass is off and I have asked numerous people for a reliable, and knowledgable person that truley knows how to dial in a compass, and guess what It is another year and ???????

I even asked at the boat and show and came up empty.

I guess I will have at it this year, though I have never done it before.

Any pro's out there that have ripped a compass apart and got her dialed in?

Help a brother out.

 

Of course, you can get a guy to come on board and make sure that youir compass is as correct as it can be using the sun . As I remember, it costs about $125 for him to come down. I will try to remember the guy's name as I have used him inthe past. he is from up around Oyster Creek if I am not mistaken.

[ 05-01-2006, 11:17 PM: Message edited by: Capt Steve ]

 

I'll do it for a lot less for the right circumstanses and probably have it more accurate unless he's doing it the new way instaed of the USCG way....

Phil...ya got e-mail...after taking one of my USCG courses...I owe it to you to clear your head and make it all better!!!!!

 

I believe there is a detailed description for swinging your compass in Chapman's.

 

THE GREEKS WERE THE FIRST ONES TO USE THE COMPASS. FIND AND OLD GREEK SAILOR AND ASK HIM TO FIX IT. HE WILL KNOW HOW, ITS IN HIS BLOOD.GOOD LUCK.