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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Help with great circle

Author Topic: Help with great circle

 - posted February 27, 2024 02:42 PM      Profile for JHweather           Edit/Delete Post 
Can you direct me to great circle test questions?
In general, resources associated with great circle sailing.

David Burch

 - posted February 28, 2024 10:44 AM      Profile for David Burch           Edit/Delete Post 
You can get USCG practice quizzes on this topic (samples below), but you will have to get the quiz to work it for the answers.

To make the quiz, go to our Starpath Resources, and in the Library section choose Practice Problems and then Random Quiz Generator, and then Topic = Navigation Problems, and then key words = great circle. then you will create as many tests as you like. I think the total number of questions is about 30 in that section. Related questions may also be in other categories.

Here are samples:

Determine the great circle distance and initial course from LAT 33°53.3' S, LONG 18°23.1' E to LAT 40°27.0' N, LONG 73°49.4' W.
A 6648.0 miles, 298.7° T
B 6743.5 miles, 302.7° T
C 6750.8 miles, 235.5° T
D 6763.0 miles, 304.5° T

The great circle distance from LAT 35°57.2' N, LONG 05°45.7' W to LAT 24°25.3' N, LONG 83°02.6' W is 3966.5 miles and the initial course is 283.7° T. The latitude of the vertex is 38°09.4' N. What is the longitude of the vertex?
A 28°02.6' W
B 28°18.2' W
C 28°46.3' W
D 28°54.7' W

The great circle distance from LAT 25°50' N, LONG 77°00' W to LAT 36°56' N, LONG 06°15' W is 3616 miles, and the initial course is 061.7° T. The position of the vertex is LAT 37°35.6' N, LONG 25°57.8' W. The difference of longitude from the vertex to a point (X) on the great circle track is 10° W. Determine the latitude which intersects the great circle at point (X).
A 37°02.5' N
B 37°10.2' N
C 37°15.6' N
D 37°21.2' N

Your vessel departs Yokohama from position LAT 35°27.0' N, LONG 139°39.0' E (ZD -9), at 1330 ZT, on 23 July, bound for Seattle at position LAT 47°36.0' N, LONG 122°22.0' W (ZD +8). The distance by great circle is 4,245 miles, and you estimate that you will average 13.0 knots. What is your estimated zone time of arrival?
A 0438, 4 August
B 2038, 4 August
C 0438, 5 August
D 1238, 5 August

Your voyage commences off Cape May, NJ, at LAT 38°40' N, LONG 74°00' W, for LAT 44°00' N, LONG 10°00' W. Sea ice is north of 45° N and west of 45° W. Extensive naval exercises will be conducted within a 150-mile radius of LAT 50°00' N, LONG 35°00' W. Which statement about a direct great circle route is TRUE? (Use gnomonic tracking chart WOXZC 5274.)
A The latitude of the great circle vertex is above 50° N.
B You must plot a composite sailing to remain south of the ice limits.
C The naval exercises will interfere with the direct great circle route.
D The shifting shoals northwest of Sable Island will be a navigational hazard on the track line.

and more...

From a practical point of view these are best solved with dedicated navigation program like our StarPilot (popular with ships for doing these computations), but there are free solutions. One to definitely consider is qtVlm that we use in this course for weather work (free app for Mac or PC). It is a great nav program that will lay out all of these GC routes so you can determine any solution, as well as etas following a GC route.

In this regard, you may find this article of interest: Great Circle Distance — The Three Options.

I should also mention that we have in those Resources high res great circle charts of Atl and Pac oceans. They are in Library / Forms and plotting sheets near the top. If you want to print them on a large paper, then check out the resources we have in this article on NCC chart printing at


From: Starpath, Seattle, WA
David Burch

 - posted February 28, 2024 09:23 PM      Profile for David Burch           Edit/Delete Post 
Just added a video that shows the qtVlm solution to each of the sample problems.


From: Starpath, Seattle, WA

All times are Pacific  
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