# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Bowditch Table 15**

**From:**Bill B

**Date:**2005 Jan 26, 16:25 -0500

Jim In my 1995 version, it is article 2203, and actually gives the correct formula for table 15 (two terms under the radical symbol)! I do not think a chunk of text is missing, as the Explanation of Navigation Tables uses a parallel format. Bill > I searched through the rest of Bowditch 2002 for more references to the > Table 15 procedure, and found this odd paraphraph in Chapter 22, Article > 2202: > > "Distance by vertical angle between the waterline and the top of an object > is computed by solving the right triangle formed between the observer, the > top of the object, and the waterline of the object by simple trigonometry. > This assumes that the observer is at sea level, the Earth is flat between > observer and object, there is no refraction, and the object and its > waterline form a right angle. For most cases of practical significance, > these assumptions produce no large errors. > D = sqrt[(tan^2a/.0002419^2) + ((H-h)/0.7349)] - (tan a/.002419) > where D is the distance in nautical miles, a is the corrected vertical > angle, H is the height of the top of the object above sea level, and h is > the observer's height of eye in feet. The constants (0.0002419 and 0.7349) > account for refraction.". > > I don't see why the Table 15 equation is given in this paragraph. Looks to > me like a chunk of text is missing between the end of "...produce no large > errors" and the equation, and that in fact the second half, which contains > the equation, belongs to a missing title that should describe "Distance by > Vertical Angle Measured Between Sea Horizon and Top of Object Beyond Sea > Horizon". Can someone check an older Bowditch?