Thursday, October 19, 2017

ASA Douglas Style Plotter

The ASA Douglas style 5" by 5" compact plotter is perfect for small craft chart tables. Customize with 1.5mm drilled holes in the center and at the upper scale. This will enable DR and celestial navigation plotting without the need for dividers. Includes reciprocal courses around the perimeter compass rose.

Sunday, October 8, 2017

Otis King Calculator for Celestial Navigation

The Otis King is a basic non electronic calculator with four place precision and is good enough to perform law of cosine sight reduction to 1' for celestial navigation and great circle sailing purposes. Easy to learn multiplication and division routines. Find for reasonable cost on Ebay.

Saturday, July 8, 2017


The Addiator is a very clever non electronic pocket summing tool. Works well for running totals or adding a series of leg distances. Ebay has many listings at reasonable cost.

Monday, April 10, 2017

Rate Adjusting a Mechanical Watch

Affordable quality mechanical watch movements such as ETA, Seiko, Miyota, and Orient can be rate adjusted to better than 5 seconds per day using a free program called Audacity. There is a learning curve to it. The how to YouTube videos are helpful. See links. 

An excellent affordable mechanical watch suitable for underway celestial navigation is the Orient Ray II divers model which hacks and hand winds.

Tuesday, January 17, 2017

Compact Ex-Meridian Tables

Here is a link to a useful Bowditch style compact ex-meridian table PDF designed primarily for Sun observations.

Tuesday, November 29, 2016

Quicker Ex-Meridian Formula

This modified ex-meridian formula saves a few moves on the K&E slide rule (solution time 50 seconds).

Slide Rule:

a = (Cos Lat. Cos Dec.) / Sin (Lat. +/- Dec.)***      
(+) contrary name  (-) same name  *

+XM' = .524 (a)(t)(t)      
t = meridian angle in degrees and tenths  **


+XM' = (a)(t)(t) / 1.91


 * The (a) value can be worked up prior to observation. 
** Slide rule tip - pencil mark the slide C scale at .524 for quick cursor set.
*** Cos (Ho) can be substituted for Sin (Lat. +/- Dec.)   Ho = corr. sextant altitude

+XM' = ex-meridian minutes of arc to be added to Ho then solve as a LAN observation.

Sunday, September 4, 2016

Ex-Meridian by Slide Rule

The ex-meridian calculation can be performed faster by slide rule than by pocket trig calculator with equal precision for celestial navigation purposes. 5 moves of the cursor and 6 moves of the slide in less than 2 minutes of time.