From Gods through Dogs and back again
To some extent the needs of the mariner are simple to define: a position line, of any shape (straight as from a bearing, circular as from a range, hyperbolical as from a radio system), tells you that you are somewhere on that line. Two lines and you have a position (but sometimes two), three lines and you have a cocked hat and some reassurance, more than three and you are more assured. The first mariners followed the coastline. They used visual marks to avoid known shoals and dangers and to identify safe havens. They added to their knowledge through use of their senses and some trial and error. There is a fascinating story to tell of the development of charts and sailing directions but that is for another day. With time mariners moved away from the coast and the familiar marks, and the challenge of ocean navigation was born. At first many placed their faith in their various gods but by the first millennium BC the Phoenicians were using astronavigation, observing the sun and the stars as they moved across the heavens. As they approached a strange shore they fell back to their coastal skills. Clouds, birds (as the crow flies), tides, currents, and floating debris all gave clues and positional information to a sensually aware mariner. The early form of lead line gave not only depth but also quality of the bottom.
Writing in about 450 BC Herodotus gave directions for the approach to Alexandria 'when you are still a day's sail from the land, if you let down a sounding-line you will bring up mud, and find yourself in eleven fathoms water'.
So with the lead line we encounter our first navigation aid. Many others would follow. Magnetic compasses may have their roots in China in about 200 BC but it seems to have been the 12th century or later before they began to feature on ocean going ships. The quadrant (fore runner to the sextant) comes on the scene in about the 10th century but was preceded by the Kamal which used a plate on a knotted cord to measure the elevation of Polaris.
These devices gave us direction and latitude, but the ability to determine longitude proved a more difficult challenge. So much so that in 1714 the UK Parliament offered a prize of £20,000 to the person who could design a 'practical and useful method of determining Longitude to an accuracy of half a degree'.
Bear in mind that prior to this countless lives, cargoes, and vessels were lost due to incorrect estimation of longitude. Probably the most unusual method of determining longitude was the powder of sympathy (pet lovers please skip to next paragraph).
The powder was said to have the power to heal at a distance but also caused pain. So if one wounded a dog and kept it on board the vessel and then, at noon in Greenwich, had a person ashore apply the powder to a bandage that had been on that wound, the dog would yelp in pain. With that yelp came a time stamp and with time comes longitude.
For reasons that are no longer clear the powder of sympathy method was dropped in favour of a the chronometer. In 1759 John Harrison's H4 claimed the prize, but the tradition of a ship's dog was alive and well until recent times-sailors always like a backup. As we will see later, time continues to be at the heart of positioning. It is interesting that in my own time at sea I have (with the exception of wounding a dog) used all of these methods to detect my position and they are all still available to this day.
- I have followed Herodotus by frequently using soundings for a position line. Indeed in making a passage from Panama to the US Gulf (a frequent route of my youth), to avoid the Quita Sueno bank, crossing the morning sight with the 100 fathom line was often the only fix available.
- I have followed the Chinese with my compass bearings and running fixes, and even earlier mariners with angles and transits.
- I have followed the Phoenicians by using sights of the sun, stars and planets for most of my career. I have even had a wise Master advise me to alter course based on sea temperature to keep the gulf stream pushing me along.
The concept of a satellite based radionavigation system was a natural development. The Global Positioning System (GPS) was born in 1973 under the leadership of Brad Parkinson, an Air Force Colonel who is frequently referred to as the Father of GPS. From 1973 to today GPS has become the prime means of fixing position both ashore and afloat. Instant, accurate positioning has become the order of the day. The differential system provided by the General Lighthouse Authorities provides an important integrity functionality and enhanced accuracy for GPS.
GPS has revolutionised navigation but brings with it a new set of problems. Mariners increasingly rely on GPS to the extent of ignoring the need to check their position by other means. The mindset is retreating further inside the bridge and away from the view out the window. Getting the watch officer more actively engaged in the navigation of the ship has been identified by the Nautical Institute as a key challenge as we move towards e-Navigation.
GPS and other global navigation satellite systems (GNSS) such as Glonass and the proposed European Galileo system are all very exposed to deliberate or accidental jamming. Small pocket sized jamming devices have the potential to create havoc in both the position and timing sectors. To overcome this the General Lighthouse Authorities and a number of other international partners have stressed the need for a complementary terrestrial system with a stronger signal on a different frequency. This requirement received support from Brad Parkinson himself at a recent European Navigation Conference. eLoran, the system recommended for this purpose by the General Lighthouse Authorities, will deliver similar accuracies to GNSS on a robust platform that is highly resistant to jamming. The old phrase 'it's not rocket science' is what gives eLoran its value.
As General Lighthouse Authorities we provide many of the aids discussed above. Visual aids for daytime and nighttime fixes, radio aids such as racons, automatic identification system, differential GNSS, and eLoran (and previously radiobeacons). Into the future we will provide differential augmentation for not only GPS but other GNSS systems such as Galileo (European), Glonass (Russian), and future Chinese or other systems. A mix of systems is critical to ensuring safe navigation. All of these aids continue to have a place within eNavigation.
Those of us who are mariners must try to remember that what we need is a position line. That such a line is expressed digitally or automatically on our electronic navigational charts does not of itself make the position or the chart data any more accurate. Check, check, and check again is still the watchword of safe navigation. Remember, at the start of this story we mentioned that original mariners used their senses to navigate safely and detect danger. These are still key navigational aids and we should not let them fall into disuse.
The first satellite in the new Galileo system has been named Giove which is Italian for Jupiter. With Giove in space we can truly say that navigation has gone from gods to dogs and back again.