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Guadalcanal 1568

Several weeks ago I discovered a book I had purchased 35 years ago at Marine Press 85 Berkely St. Toronto. It was neatly filed in my adventure sailing section. “Pacific Odyssey” by Gwenda Cornell was a wonderful read during this lock down time in the world. Gwenda and her family traveled by sailboat all through […]

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RTL-SDR for AIS

Introduction AIS Automatic Identification System for Ships is a traffic system that uses VHF transponders on vessels to periodically send out location information. It was developed by Swedish inventor Hakan Lans and is similar in concept to the ADS-B transponder system used on aircraft for position reporting. AIS uses two VHF marine channels 87B (161.975 MHz) […]

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Celestial Navigation Basics – Hc Calculated Altitude

In this post we will look at how to determine Hc the calculated altitude and compare this to Ho the observed altitude. The difference between Ho and Hc is the intercept and is used in the Marc Saint Hilaire method for solving position. In previous posts we found Hs (Ref.3), Ha (Ref.4) and Ho (Ref.5). […]

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Celestial Navigation Basics – Ho Observed Altitude

In this post we will look at how to reduce a sextant apparent altitude Ha to an observed altitude Ho. In the following post, we will look at how to calculate Hc. Ho will then be compared with Hc to determine an intercept. The complete details are contained in Ref.1. Complete Sight Reduction procedures are […]

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Celestial Navigation Basics – Ha Apparent Altitude

In this post we will look at how to reduce a sextant altitude Hs to an apparent altitude Ha. In the following post, we will look at how to reduce Ha to Ho. Ho will then be compared with Hc to determine an intercept. The complete details are contained in Ref.1. Complete Sight Reduction procedures […]