Yachtmaster Question?

[Medskipper]

I am reading a yachtmaster excercise book to brush up a bit and I thought I knew what I was doing with regard to variation and deviation, but I just cant arrive at the same answer that my book gives for this particular question. Can anyone tell me what they think the correct answers should be and I might be able to work out where I am going wrong!

Question: A boat steering 223 degrees C takes the following bearings using its steering compass. Convert these bearings to true. Variation is 8 degrees west.

A. Church 358 degrees C. Deviation 5 degrees East
B. Tower 265 degrees C. Deviation 2.5 degrees East
C. Lighthhouse 134 degrees C. Deviation 3 degrees West

Now I am pretty sure that when working from compass (C) to true you should add East and subtract West.

Post your answers and indicate how you arrived at your answers and in a couple of days I will post the answers that the book gives. Unfortunately they dont show how they arrive at their answers! Even though I have their answers I cant see how they can be correct!

Best of luck

Barry

<hr width=100% size=1>I just want to retire with my boat to the Med!

 

[ccscott49]

Variation east, compass least = add east variation to compass azimuth to give true.
variation west, compass best = subtract variation from compass azimuth to give true. This I know for sure, but I'm not so sure about compass deviation, but if it's the same for compass deviation. then
A) 358 + 5 - 8 = 355
B) 265 + 2.5 - 8 = 259.5
C) 134 - 3 - 8 = 123
But to be honest I'm not sure about the deviation bit. With my compass setup I tend to ignore deviation, as it's max 1 degree.
if deviation is applied the other way, then,
A) 358 - 5 - 8 = 345
B) 265 -2.5 - 8 = 254.5
C) 134 + 3 - 8 = 129
Bloody hell, I'll obviously have to swot up before my exam!!

<hr width=100% size=1>

 

[jimi]

I always remember CADET Compass ADd East True

<hr width=100% size=1>

 

[duncan]

345, 254.5 and 129
workings - pointed boat at each mark and read bearing off chartplotter

<hr width=100% size=1>

 

[burgundyben]

TVMDC

going from true thru var to mag thru dev to comp then west is best so add it on

adding west when going left to right across TVMDC, subtract for east, vice versa when going CDMVT

church is 358 C 003 M, and 355 T

tower is 265 C, 267.5 M, 259.5 T

lighthouse 134 C, 131 M, 123 T

oh I hope htis is right



<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.<P ID="edit"><FONT SIZE=-1>Edited by burgundyben on 27/06/2003 14:46 (server time).</FONT></P>

 

[Deleted User YDKXO]

C'mon, its 10yrs since I did this (does anyone do this anymore?) but

A. 358 - 5 + 8 = 001deg.T
B. 265 - 2.5 + 8 = 270.5 deg.T
C. 134 + 3 + 8 = 145 deg.T

For what its worth, I dont see how the deviation can be different for each bearing because I thought deviation was dependent on the course being steered and that does'nt change

<hr width=100% size=1>

 

[Renegade_Master]

"Now I am pretty sure that when working from compass (C) to true you should add East and subtract West".

Think its tother way Barry "East is least West is Best" as I recall?



<hr width=100% size=1><A target="_blank" HREF=http://www.suncoastmarine.co.uk>Sun Coast Sea School & Charter</A>

 

[ccscott49]

Re: Yachtmaster Question? *DELETED* *DELETED*

Post deleted by ccscott49

 

[burgundyben]

Well done Mike, I think that explains it, the deviation should be applied as per the deviation card for the boats compass at the 223 being steered by the boat.

But Barry does not give us that, Barry,m you need to apply deviation for 223 C to each of the bearings. Think that might get you the right answer.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Deleted User YDKXO]

I guess your response was to SunCoast's post but the large variety of responses here demonstrates why we all buy chartplotters!

<hr width=100% size=1>

 

[oldsaltoz]

C.A.D.E.T.

C = Compass magnetic reading.

A = Add West is best = plus, East is least = minus.

D = Deviation.

E = Error, as in compass error, as per card may be plus or minus.

T = True.

Work from C to T for compass to true.

Reverse the order to calculate true to compass.

I hope this helps, put the word CADET next to the compass rose on charts.



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[BarryH]

I may be wrong and an open to suggestions here, but how the hell do you get an accurate bearing using the steering compass. I've just looked at my steering compass. I can't see that you could get those bearings from it if it was sited where it normally sits at the helm.

And the other thing. Would it not be better to use the hand bearing compass where deviation is less of an issue. Yes I know the exercises are designed to make the student work with variation and deveiation. Its the context of the thing. I've never taken a bearing for a fix with the steering compass.

<hr width=100% size=1>

 

[duncan]

they are not asking for a practical response - it's a theory test! Maybe the bearing compass has deviation built in form it's case or something but most probably someone wanted to get both deviationand variation into the test and had only one question left to do it.

<hr width=100% size=1>

 

[Deleted User YDKXO]

Agree with you. Its a stupid question. Probably dates back to the old yottie days when the steering compass was on deck

<hr width=100% size=1>

 

[Blue_Blazes]

Re: TVMDC

Same answers as Ben.

I find it easiest to relate the deviation and variation to each other so if both W or both E add them together. If one is E and one is W subtract the lesser from the greater. Then apply the result of that sum to the compass bearing, subtracting if the sum equals a Wesrerly combined dev/var, or adding if Easterly.

Hell that sounds more complicated than it really is. I know what I mean anyway.

Bill.

<hr width=100% size=1>One of these days I'll have a boat that WORKS

 

[tcm]

Re: UNderstanding, not parrotting

ok, look.

Lets say you are looking at a chart of UK. True North is at north pole. Let's say that Magnetic north is somewhere in Greeenlandish. So on this chart, that means the variation is therefore 6 degrees West. In other words, magnetic north seems from here to be 6degrees to the west of true north.

This means that if a compass (with no "wrongness" aka variation) which said yup, that's North! 000M or 360M - would actualy be pointing 6degrees west of true north : at 354T.

Perhaps think of this like a clock. The compass started counting "too early", for a westerly variation, or "too late" for an easterly. The compass says 360 - but (if a westerly variation) it "started counting" too early: six degress too early. So now that it says 360, it is reading too high - it's only 354.

If a compass 180M and the variation was 5degrees west -it would really only be 175 true - cos the compass again started counting "too early" - it reached a bigger number by the time the boat was on a true heading of 175T.

Likewise, if the compass says 180, and the variation is 3degrees *east*, then the compass starts counting too late. It's really 183True.

So, to turn a compass (magnetic) course to true, you subtract the westerly variation. Or you add the easterly. You can make a westerly as a "minus" the easterly.

parrotywise, Compass add deviation East = True , CADET

Conversely, from the chart we have a course to steer of say 5 degrees = 5T. But our poxy compass has net variation of 6 degree west. Remeber, our compass, if westerly variation, starts counting "earlier", before zero degrees, and we have to allow for that. So, we have to overcompensate, and steer 011 on the compass.

Deviation works the same way, buit varies with heading. Note that this is the deviation of the crappy ships compass, so a handbearing compass is (at least examwise) showing real magnetic, and only the variation need be allowed, not deviation.

From a ships compass, if the variation on the chart is 6 west, and deviation is 6 East, the compass is spot on true. Net the figures to find the compass error.

A: The net variation is 3 degrees west. It's from his compass so whilst the compass is pointing 358 it started counting at (true) -3 degrees. So really and truly, it's only 355T.

Parrotywise remeber Compass Add Deviation East True. The deviation is 3 west, or -3 east
so 358 (-3) = true = 355

B. Tower 265 degrees C. Deviation 2.5 degrees East, variation 8 west. Net 5.5CE west. The compass reads 265M, but remeber that the net is west. So the compass started counting too early, 5.5 degrees before zero true. The true bearing is less, only 259.5T

C. Lighthhouse 134 degrees C. Deviation 3 degrees West. variation 8 degrees west. Here, the compass is reading net 11 degrees west of True. The compass error is 11 degrees W. It started counting 11 degrees too early. Lop off those 11 degrees to get the true bearing = 123T

Or parrotywise cadet, the easterly variation is -11
compass add easterly = true
134 (-11) = 123T

Obviously, as Deleted User says, he must have jumped onto differnt boats, or had a loony on board buggering about with the compass as each bearing was taken, cos the deviation doesn't vary on a constant bearing.

Also, the q shows why peopel stay in the solent - not enuf towers, churches or lighhouses elsewhere.


<hr width=100% size=1>

 

[ianainge]

I concour with tcm, cant see how duncan got those answers though?

<hr width=100% size=1>

 

[duncan]

you'd have to see the glass as half empty............even a chartplotter has deviation and variation!
how about we forget the maths and i buy you a pint at the BA - I am heading off now to make sure I hit the most traffic possible (?).......If Sat's halfway decent I expect to be in the usual spot - only waving at Sappho as well this time round.

<hr width=100% size=1>

 

[ianainge]

no can do working this weekend but catch up with you soon.

<hr width=100% size=1>

 

[Medskipper]

Re: UNderstanding, not parrotting

Hi TCM,

You got to the same answers I got to but when I check the answers page they give:

A. 348 T
B. 255 T
C. 124 T

No I dont have the wrong page! I guess it must be a misprint or something. Their answer in each case is 10 degrees less for each bearing! I thought I was going crazy! Thanks for all your help, I know with all the modern equipment these days it does not seems to matter any more, but its good to know that there are a few people out there who can still work bearings out manually!

Barry

<hr width=100% size=1>I just want to retire with my boat to the Med!