Celestial nav at sea using a 13-year-old calculator.

On a recent passage from Norfolk to Bermuda, I had the opportunity to use my 13-year-old Texas Instruments TI-35 calculator to reduce our sun lines of position.

At only a hair’s breadth above novice status as a celestial navigator, I wanted to use an electronic calculator for my sight reductions. I was used to this approach, as I had used my home computer to reduce my practice sites back in Pittsburgh. I wrote a Basic program for my PC that calculated the distance (Hc) and direction (Zn) of other ham radio contacts. The formulas used are the same as those found in the front of H.O. 229.

Before our departure, I was quite prepared to use sight reduction tables and universal plotting sheets that I had practiced so thoroughly with in my back yard. By the way, the position of my yard is very well plotted, I have done more than 100 practice bubble horizon and artificial horizon sights and sight reductions. I then found that my $15 scientific calculator could well handle the calculations I needed. It was just a matter of learning the proper keystrokes.

By using our indicated position from our GPS as an assumed position, I was able to verify our position in a few minutes’ time. Of the sights I took on our trip, my ability to take and reduce a sight varied from as much as 2.5 miles to as little as 0.5 miles from our indicated position. So I wouldn’t get lost in the calculations, I used the Celestaire H.O. 229 Sight Solver card line for line, except for the lines that asked for inputs from H.O. 229. Calculated Hc and Ho were handled the same way.

The benefits to calculating sights for an actual position is that it gives immediate reinforcement to good sights and showed poor reductions clearly. It was not my plotting ability that dictated my accuracy, but only my sextant handling.

I highly recommend the usual practice of plotting a sight from an assumed position if you don’t have an appropriate scientific calculator to work out the sights from your DR position.

Having the ability to determine a position out there, and out there is pretty far, certainly made us far more comfortable in our passage and our landfall! n

Michael Shane sails aboard Scott Hopkins’ Beneteau 393, Last One, and lives in New Brighton, Penn.

By Ocean Navigator