• svglaciergem

Celestial Navigation - 3 Star Fix by HO229 Method

Updated: Feb 21

We recently had the opportunity to take a three star sight at morning nautical twilight. Our reduction method was HO 229. The resulting position was about 2.8NM from the GPS position. That isn’t bad at sea…but we weren’t at sea, we were on stable dry land! Usually a land based fix is within about 0.5 miles or better under good conditions. I suppose the outside temperature (15F) and the obscured horizon had a bit to do with it…ummm….yeah we’ll go with that excuse!

The forms used here are my own design. I like to use forms because they organize the work for those days where fatigue or distractions are present. They result in a voyage record that can be traced back to a possible source of error that was not discovered until several days later. The top form organizes the solution for either HO229 tables or direct calculation. The bottom form plots the resultant lines of positions of the observed objects. I actually don’t use HO 229 very often. I prefer a direct solution using a scientific calculator and the law of cosines…it’s faster and less likely to introduce human error with the tiny print found in HO229 tables. We carry the tables mostly as a backup to the calculator. We also have a slide rule that we sometimes use instead of the calculator!

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