Category: Navigation

Calculating Local Hour Angle (LHA)

When trying to solve the PZX triangle, we need to know the LHA. This is simply the angle between our Longitude (by EP) and the Sun’s Longitude (called its Greenwich Hour Angle, GHA).

LHA West


In this example our Longitude is 10° W. The GHA of the sun is 60°. The diagram shows that the angle between us and the sun must be the GHA – our Longitude.

 LHA = GHA – Longitude (if Long is West)


 LHA = 60° - 10° = 50°


Read more: Calculating LHA

Category: Navigation

The trouble with GPS

GPS Unit Every year, thousands of GPS sets get purchased. In the guise of handheld units, car
 navigation systems, integrated yacht systems, chart plotters, mobile phones and
 much  more. We implicitly assume they will work. We pay no subscription, and merely
 assume  the right that GPS will be available for us to use.

 The American military GPS (Global Positioning System) has been with us in excess of
 30 years. It has not only revolutionised navigation at sea, but also in our daily lives. Most cars are fitted with ‘Tom-Tom’ type devices for land-based navigation. Emergency services all use GPS for quick location of casualties. Couriers and transport companies all use GPS to track shipments. Our smart phones use GPS to give us a whole host of information from local weather to our closest chandlery or Chinese restaurant.

Read more: The trouble with GPS

Copyright 2011 All about sailing - Navigation. All about sailing
Free Joomla Theme by Hostgator