Sight Reduction Tables Pub 229 v Pub 249

[Sailing Aphrodite]

Over the winter I have been getting my Celestial Navigation up to speed.

I have a few passages planned over the summer that I will have time to do some old fashioned navigation with sextant and universal plotting sheets. Ultimately this is for a RYA Ocean Ticket sometime in the future.

I've been looking at both the Pub 229 - Sight Reduction Tables for Marine Navigation and Pub 249 - Sight Reduction Tables for Air Navigation.

While both publications have the same data with different layouts I would be interested to hear if anybody has a preference or is it just what you are used to?

[P.Rutherford]

In practice Pub. 249 is faster to use but Pub. 229 will provide more precise results.

249 was designed for Air navigation since aircraft move much faster than a sailboat or ship and a position, fix or LOP is always way behind you and must be adjusted for the distance from the shot taken and estimated present position. 229 was made for marine navigation but, for our purposes, it doesn't really matter which you use. For sailors, accuracy of a position is often decided by the accuracy of the shot and the sextant's state of adjustment.

Now Pub. No. 249 Volume 1 is for navigational stars is is really easy and quick. However, Volume 1 must be updated to the latest version after a certain number of years.

Having said that, Pub No. 249 is the only one I use and not Pub. No. 229. In terms of overall size- 249 is found in 3 volumes and 229 is 6 volumes- that's a lot of paper.

With 249 you can print out the latitudes wherein you'll be sailing.
With 229 you can print out the LHA's within latitudes of 7° (regardless- that's a lot of paper). Or....you can carry the 229 volumes you need (more paper)

You can find both 249 and 229 here;

Pub. No. 249
https://thenauticalalmanac.com/Pub_No_24..._2025.html

Pub. No. 229
https://thenauticalalmanac.com/PubNo229.html

Paul

[PeterB]

Pub 249  (A.K.A. H.O. 249) Volumes II and III are commonly used for sight reduction.  However they only cover celestial bodies with declinations between 0 and 29 degrees.  This is sufficient for most navigation and always includes the sun, moon and navigation planets.

If you want to, or must, do sight reductions for bodies outside of that range of declinations you can use Pub 229 but you can also use tables which are now included in The Nautical Almanac or do the calculation with a scientific calculator.

Most introductory cell nav books seem to reference Pub 249 volumes II and III.  Those two volumes are fairly compact, easy to learn, and accurate enough for practical navigation.  They are available in spiral bound form or paper back form.

Pub 249 Volume I is a slightly different thing than Volumes II and III.  It lists 7 selected stars (no sun, moon, or planets) based on your local hour angle of Aries and your latitude. You pick out three that you think you will be able to see accounting for things like cloud cover and objects that may be blocking your field of view.  It gives you an altitude and azimuth that will be pretty close to what  you will see when you take that star.  After accounting backward for refraction and height of eye if you are using a sea horizon you set  your sextant to the predicted altitude and look in the direction of the listed azimuth and you should pick up the star in your optics.
  That all sounds grand, but because it is dependent on the local hour angle of Aries at the time of  your sight it makes your sights time-dependent as well. In other words you have to plan out at what time you will be taking the sight and what your estimated position will be at that time.
  There are methods of using 249 Vol I to do sight reductions but they differ somewhat from the use of pub 249 Vol's II and III or Pub 229. I am not personally very familiar with them other than to know that they do exist.

  The upshot is that if you are seeking to purchase hard copies of Pub 249 you really don't need to buy Vol I  unless you would like to have it for planing purposes.  In that simpler case (not depending upon it for sight reduction) it doesn't matter if it has gone out of date.  It will still give you a pretty good idea of what stars will be visible to you for a given LHA Aries and latitude and about where to look for them.

PeterB