When you stand outside, on a ship, in the middle of a vast expanse of water, you become completely disorientated because there is nothing in any direction with which to orientate yourself. On land you are nearly always within sight of something notable – a hill, a copse of trees, a road or a church tower – something that can help you to know where you are. With a map, a compass and a few of these local landmarks it is comparatively easy to find your way home.
Of course, many people these days will have SatNav (Satellite Navigation) in their car and just rely on that – although I am not one of them. I much prefer the challenge of getting where I want to go using just the power of my brain – even though it may take a few hours longer than expected and cost a lot on fuel!
Ships are also dependent on SatNav to find their way around the oceans when they are far away from land. The system uses a network of satellites high above the Earth. Some satellites orbit the Earth (move in big circles around the Earth) whilst some are geostationary (they stay above the same spot on the Earth at all times). The satellites continuously transmit signals which can be picked up by any SatNav receiver. A long as your SatNav can receive from 4 satellites it can work out where you are on the Earth’s surface, whether you are on land or at sea. From where the Joides Resolution is drilling at the moment, we are receiving information from 8 different satellites!
A ship’s SatNav system is very similar to a car system. It tells the Captain what direction he needs to go in. Of course the Captain constantly has to check that this is correct – just like in a car.
If you know where you are you from the GPS system, you can pinpoint your position exactly on a chart (the equivalent of a map on land) and then use your compass to guide yourself to land. However, there is always a risk that something could knock out the satellite system – perhaps a Solar storm could happen and cause this. A Solar storm is when a storm on the surface of the Sun sends lots of energetic particles towards the Earth that interfere with electrical signals. Just in case this happens mariners still need to be able to use the equipment that has been used for hundreds of years, the main one being a sextant.
NavigationA sextant is a clever device with which you measure the height from the horizon to a known star (or the sun during the day). Once you know this, and you know the time of day or night it is, and the time of year (because stars change their position thoughout the year) then you can work out where you are and which direction to move in.
There is a famous story that is well worth finding, about an ill-fated expedition to the Antarctic organized by Shackleton in 1914 where a sailor’s skill with the sextant saved many lives. The original expedition ship – the Endurance – became trapped in ice and had to be abandoned.
Three small boats headed out into the cold, wild Southern Ocean where there are just a few scattered islands and very occasion whaling boats passing. They eventually landed on Elephant Island – little more than a barren rock with no food and very little shelter. With winter approaching, Shackleton had to make a difficult decision – to take one of the boats and head once again out into the ocean to try and make South Georgia, a larger island where there was a regularly stocked whaling station. The distance was an incredible 800 miles in an open boat! One of the crew he took with him was the Captain of the Endurance, a man named Worsley, who was experienced in using navigation equipment.
On the course of their tortuous voyage Worsley managed only about 5 sightings of the sun through swirling clouds and mists but even so, he managed to steer the small boat to their destination and find a boat able to go back and rescue their stranded shipmates.
Worley’s navigational skill, and the amazing design of the sextant – which is little changed to this day – were real heroes! Hopefully, our Captain, Steve Bradley won’t have to do this during our expedition. But if in the awful event of us having to abandon ship, there will be a sextant on board every lifeboat, just in case!