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Navigation: - explanation to Belmore South pupils in September 2005 ... “we have a satellite Global Positioning System (GPS) for navigation and that shows us the way even at night. It needs electricity or batteries to run, but if it breaks down, we can navigate using the sun and the stars and a paper chart, a pencil (yeah, really!) and an instrument called a sextant which measures the angle of the sun and the stars in the sky and, with the help of a good watch, allows us to calculate where we are. We have a magnetic compass as well and at night, we point the boat in the direction we think we need to go. If we know where we started from and our speed and direction (our velocity), we can work out where we have got to by morning. This is called Dead Reckoning and it is not as accurate as GPS but it works.