Voyagers enjoy emergency sun tool

Tony Crowley’s recent article on sun sights (“Emergency sun navigation,” Issue No. 108, Sept./Oct. 2000) was an excellent refresher to the basics of navigation. To navigate with only a watch, some folded paper, and simple memory aids is very useful.While anchored here in Kilifi, Kenya, we’ve been constructing the recommended paper device to observe the zenith distance of the sun; but Crowley cited three different proportions for the paper to get the basic 40-degree fold: 21 x 25 cm (0.8400 ratio), 8.5 x 10 (0.8500 ratio) and 5 x 6 (0.8333 ratio). Concerned that these differences might affect the accuracy of the tool, we searched aboard our boat for a source of trigonometric functions. To our delight, we found that our well-worn copy of Nathaniel Bowditch’s American Practical Navigator (1962 edition) came to the rescue again. Consulting his table of tangents, we learned that the differences induced by this range of proportions is only about 1/2 degree (the 21 x 25 sheet is closest to exactly 40 degrees), and such differences are well within an acceptable margin for the purpose advertised. We commend Crowley for a succinct and useful article.