A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2016 Oct 29, 02:00 -0700
Gary, could you work through one rhumb line problem from beginning to end using your equations, so that I have a model to follow as I try and sort out how to do this myself? It will help me spot elementary errors if I know what the right answer should be to a particular calculation.
Thanks so much,
I am attaching a photo of my computation using the original data from your page 45, see my prior posts:
I worked the example on my Pickett N 3-T sliderule and I kept coming up with a problem at the very last stage where I had to divide 190.1 by the cosine of the rhumb line angle, 82.45 degrees, my resulting distance was significantly different from the example I did in my prior post, I kept coming up with 1430 nm and I know the correct answer is 1444 nm. I have attached a photo of that portion of the cosine scale of that sliderule. It took me a while to figure out the problem, the cosine scale is marked incorrectly! Who whould have thought that a Pickett rule would have an error on its scale. If you look carrefully you will see that the 82.4 mark is long and the 82.5 mark, that should be the long one is short. I was seeing the long mark as 82.5 and positioning the cursor to the right of it, actually at 82.35. After I found this out I computed the rhumb line distance as 1450 nm, only 6 nm different from the computation done with a computer to many more decimal places. Apparently someone discovered this problem because the long ".4" line was eliminated on the identical, except for color, yellow Pickett N 3-ES. But this time they eliminated the long line altogether, not the 82.4 nor the 82.5 mark is long. I have attached a photo of this rule too.