NavList:

Here are the answers as they appear in Ocean Navigator with my answers, where they differ from ON, given in parentheses

A. GMT of LAN 15h35m20s (15h34m58s)
B. Hs 73d44.9’
C. Latitude 25d11’N (25d14.3’N)

The ON result for latitude is quite a bit different from both what I get with the Nautical Almanac and from Frank’s 25d14.6’N using 19th century methods.

Let me also say that I agree with Stan K’s pet peeve about the calculation of LAN. In all examples I have seen it appears to have been calculated by converting longitude to time and then adding or subtracting a whole number of minutes obtained the listed “Mer. Pass.” entry for the day. I produced my result by interpolating the “Eqn. of Time” which is available in the NA to the nearest second at 12 hour intervals. Of course a few seconds are neither here nor there for the noon sight but it does grate on me that answer is quoted to a misleading level of accuracy. Glad to hear from Stan that this has been addressed in the latest edition.

Given the ON answers above you can work backwards to find what value of the Sun’s declination of the must have been used. This comes out be 8d55.9’N which is exactly the declination listed in the Almanac for 12h GMT. Coincidence?

Unfortunately over the limited period that I have been subscribing to Ocean Navigator errors of one type or another don’t appear to be very uncommon. The November/December 2012 edition contains a problem in which a value of Hs of 38d28.8’ yields a value for Ho of 21d46.7’.

I also have doubts about some others. October 2012 has a nice LOP problem using Mars and H.O.249 asking for Ho, the intercept and EP. I agree reasonably well with the EP but cannot reproduce the quoted intercept. I get 6.7nm towards vs. ON’s 12.7nm towards. March/April 2012 also has an LOP problem for which I get an intercept of 17.2nm towards. The ON answer is 16.2nm towards. Maybe they are typos or maybe I just screwed up.

If I had a point it would be that I find it rather sad that one of the few readily available sources Celnav problems can be have these sorts of issues. It must be discouraging for those trying to use them to learn the practice.

Robin Stuart

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