Offshore Navigation Committee
Frequently Asked Questions

 

Following are some questions that are frequently asked of the ONCom.

 

For questions concerning The Capn or Visual Passage Planner 2 software, check the N09 Software FAQ web page.

 

 

 

1. QUESTION:  What needs to be labeled on the celestial meridian diagrams in my N2002 sight folder?  N93/94 showed a sample meridian diagram, but there is no comparable diagram in N2002.

ANSWER:  For each submitted sight, except for the meridian transit sight, you need to complete a meridian diagram on the back side of the sight reduction form. For this diagram, the only labels you need to add are Pn, Ps, Q and Q'.  The Z, Na, N and S labels are already preprinted on the form, so you don't need to label them again.

2.  QUESTION:  Why does my exam critique say that I took a re-exam, when this exam was the first one that I've taken?

ANSWER:  This happens when a student orders a multi-part exam, but does not use one of the parts.  The unused part is returned to USPS Headquarters, along with the completed part of the exam.  When another exam is ordered for the student to "replace" the previously unused exam, the Headquarters computer checks its data and finds that an "original" exam has already been sent to this student, and marks the subsequent order as a "re-exam".  This record is passed to the exam grader and reviewer, and is then used on the critique sheet.  Don't be concerned though, because the educational records show that you completed the exam the first time through.  Hopefully, this will clear up the confusion about "re-exams".

3.  QUESTION:  As taught in the N2002 student manual, I drew circular arcs on the celestial meridian diagrams for my sight folder.  When the sight folder was returned to me, the arcs and perpendicular construction lines were marked as being in error, even though they were drawn correctly.  Why were they marked wrong?  Did the exam grader use a computer program such as Plot Tools, which draws elliptical arcs, to grade my diagrams?

ANSWER:  Your question about the use of circular versus elliptical arcs is a good one.  Most of our graders and reviewers do not use computer programs such as the Plot Tools program when they do their work.  The vast majority instead rely on the same manual methods as students use in preparing their sight folders. The reviewer in this case checked your arcs and the corresponding construction lines against the answers for Zn on your sight reduction sheets.  Since the diagrams showed Zns about thirty degrees different from the computed Zns, the vertical arcs and corresponding construction lines were red checked.  At higher altitudes, circular arcs become very inaccurate compared to elliptical arcs.  Students should check that the values for Zn and t/LHA from the diagram approximate the values for Zn and t/LHA as obtained in the sight reduction calculations.  If the values don't compare favorably, check that the constructions were done properly.  Our graders and reviewers have also been advised not to red check meridian diagrams with this problem unless the construction is in error.

4.  QUESTION:  May I include more than the one required observation of a body at Meridian Transit in my N sight folder?

ANSWER:  By all means, yes!  We encourage students to take more than the minimum number of sights required for any sight folder requirement, since these could serve as replacement sights should the reduced sight(s) not meet the basic requirement for whatever reason.  We have always encouraged students to do this, especially for Meridian Transit sights, where the minimum is only one sight.

5.  QUESTION:  I've used the NavChk program from the USPS web page to verify my sight reductions.  Should I include those printouts with my sight folder to save National some work?

ANSWER:  Extra material should not be included with your sight folder.  That includes any computer- or calculator-produced printouts or plots, such as that provided by either NavChk, Plottool, or Celestial Tools.  While we appreciate the thought, we need to provide completely independent review of sight folder data and information.  This independence pretty much rules out using student- or sight checker-provided information.  Please do not include materials other than what is required with your sight folders.

6.  QUESTION:  I seem to have different versions of some N forms from those shown in the USPS manuals.  May I use these different forms?

ANSWER:  As our forms are updated to better suit our N course, differing versions of USPS forms may appear in your student kit (or on this web page).  Please be advised that you may use an older or newer version of a USPS form for ONCom work, if it still applies to the subject at hand.  For example, you may use an older SV92 form or a newer SV99 form when you submit your sights.  The same applies to deck and sight logs and to the key to N sights (NSK) form.  So don't panic if you get a version of a form that is newer than the date of your student folder; just go ahead and use the form as you normally would.  If you have questions, please contact the National ONCom Chair.

7.  QUESTION:  When does the meridian angle of the body I am shooting for my N09 sight folder have to be at least 10 degrees away from my (observer's) meridian?

ANSWER:  This requirement only applies to the sights for the two body fix for N09, and is necessary so that the sight data is close to being a straight line function within the time period required giving a more accurate fix.  This constraint does not apply to the remaining N09 sights.

8.  QUESTION:  May I use electronic means (e.g., GPS) to determine my known position for my sight folder?

ANSWER:  Yes, you may use electronic means to determine your known position for sight taking.  You may use GPS, LORAN, RADAR, etc. as you see fit.  You are responsible for ensuring that the electronic receiver is functioning properly and that the electronic system is accurate enough.  Because there has been some confusion about this topic, clarifications will be included in the next edition of JN and N.

9.  QUESTION:  For my N sight folder, may I use stars other than those listed in the "Index to Selected Stars" that appears at the beginning of the Nautical Almanac?

ANSWER:  Yes, for N you may use any star that has its Sidereal Hour Angle (SHA) and declination (dec) listed in the back of the Nautical Almanac (normally found on pages 268-273).

10.  QUESTION:  Which, if any, sights do I circle in my sight log for the sights used in the two body fix for N2002, where two runs of five sights each are averaged in determining my Fix?

ANSWER:  Circle each of the sights that are used in the averaging process.  This clarification is provided on the reverse side of the Sight Log (SL98) form, item 1.

11.  QUESTION:  May I use a night vision scope to view the horizon when taking sights for my sight folder?

ANSWER:  Both JN and N will continue to teach traditional celestial navigation.   Accordingly, use of night vision equipment will not be allowed for sights submitted in sight folders.