500T NC Upgrade Nav Problem

I’m self-studying for the upgrade from 100T to 500T and have been stuck on a few problems. I’ve exhausted all of my resources and hope that someone out there is willing/able to explain how to solve one of these problems. The problems are all looking for compass deviation given various celestial information, and I think my problem may lie with not having the necessary materials in my home to study for this. Anyway, one of the questions is:

On 1 September your 11115 zone time DR position is LAT 25 20.0’N, LONG 28 24.0’W. At that time, you observe the Sun bearing 160.5psc. The chronometer reads 01h 14m 58s, and the chronometer error is 01m 17s fast. The variation is 13.5W. What is the deviation of the standard compass? The correct answer (according to the guide) is 2.1E.

This test (more specifically, these few problems) are all that stand between me and the 500 ton near coastal. Any information you have would be greatly appreciated.


That’s an azimuth. There are ample instructions in Bowditch II. There are two different ways to do it: by equation calculation and by triple interpolation using a 229. The 229 is more work but not as easy to screw up in my opinion. If it were an amplitude the celestial body would be on or very near (depending on the problem) the horizon.

It is my understanding, that 500 NC does not have Celestial Nav problems. I am supposed to take tests tomorrow.

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Did you test yet? How was it? Were there cargo and stability questions? I’m trying to pass this with just self study as well.

I didn’t think so either, and maybe they’re giving me the oceans test, but the letter to test says for NC. A really nice guy turned me on to “The Cutterman’s Guide to Navigation Problems” and it is helping more than I ever thought something could. The site he sent me the link to was at scribd.com. Downloading copies of Pub 229 and the 1981 Almanac have also made studying much easier.

On my test for Deck General (I believe) there were a few basic questions on cargo and stability, but nothing too in-depth. Its been a few weeks since taking those portions of the test for me, so its hard to recall any specific questions on it…the noggin is too cluttered with Azimuth and Amplitude problems at the moment. I’m heading in tomorrow to take another crack at the Nav Problems. All the best on your test tomorrow!


The T-Nav modules (205 & 145----as I recall) do indeed have azimuth and amplitude for compass correction questions. Usually, but not always, one of each.

Since you will be able to use Bowdich Vol II in the exam room , you should learn one or more of the methods shown in Bowdich. I suggest that find someone that knows to teach you how to do these.

I taught myself all of it with Lapware. I would recommend it to anyone. It is all in Bowditch as well. You will most likely have one of each with Amplitude and Azimuth.

There is a simple straight forward example of how to do an azimuth inside the cover of a Pub 229, (how to do celestial LOPs also BTW). Learn it that way and your notes (Pub 229) will be with you in the exam room. (True with PUB 9 Vol II also)

Be advised, in the problem you site, the bearing to the sun was taken “psc” “per standard magnetic compass”, not on a gyro compass.

Once you master this AZ thang, it’s a hop skip and a jump to doing celestial fixes. Think about doing yourself a favor and get an oceans endorsement cuz you’ll be most of the way there.

gmt 13-13-41 01sept
gha 18’26.1 dec 8’11.7
lha 350’02.1
z 149.1
zn 19.1

This has been beat to death, yes there may be amplitudes and azimuths as how else could you determine deviation 200 miles offshore?

I recommend solving via equation as triple interpolation really doesn’t make sense to me. I always however Check the tables to make sure my calculated answer “makes sense.”

Important to note that often the correct answer on these questions is the closest answer, there is (in my experience) rarely the EXACT right answer.

[QUOTE=z-drive;138505]…Important to note that often the correct answer on these questions is the closest answer, there is (in my experience) rarely the EXACT right answer.[/QUOTE]

The “exact” right answer will depend on how you solved the problem. For many types of problems, there are more than one method and they yiel;d slightly different results. Also, since many of the problems are “static” in that the process and technoliogy hasn’t chnaged in a long time, the problem might have originally been written when it was solved using logarithms (Table 1 of Bowditch) or a slide rule (I first learned using logarithms as I had an old school nav instructor (“HAP”) who detested calculators). That will also yield a slightly different result.