Going back to the 15th century and the amazing voyages of Portuguese Vasco de Gama and his opposite number from Spain, Christopher Columbus, trying to reason how they accomplished what they did with such small ships, without charts or maps, without proven navigation instruments, is just absolutely incredible. In 1492 on Columbus's first voyage to the New World he supposedly used

an 'Astrolabe' such as this one. I guess someone on board knew how to read it and be able to understand the jolly thing. Columbus sailed in the 'Nina' which was only 30 to 40 tons, 35 feet in length and 12 feet across the beam, to the New World, but navigation would not have been a real option back then, as they only had a sketchy idea of where they were going or what was likely to be in their way. I guess it was a matter of sailing on until you bumped into something? Today, with point to point navigation, it is a much more precise and calculated event. It would have been more the case of keeping the sun on your right hand side, so to speak. Quite obviously, they learned a lot as they went their merry way and adapted accordingly.

In the 17th century mariners were using different Astrolabes etc, which became more developed as time went on. With regard to the 17th century, ships like the 'Batavia' in 1629 were using a more sophisticated Astrolabe such as the 2 which were brought up among the artefacts recovered.

These were now starting to resemble what we know as the sextant. Referring back to the fact that they could only reasonably find their Latitude position and were at a loss to know where they were in reference to their Longitudinal position. Their main objective was to measure the angle of the sun in respect to the horizon at given times throughout the day, to work out their latitude. In the case of the VOC (Dutch East India Company), the Captains were told to stick to the Company 'Weg' or Wagon Way for so many days or weeks, then turn north towards Batavia. No one gave any thought to the varying strengths of the 'Roaring Forties', so when the Captain recorded the distance travelled each hour or day, the distances achieved would vary greatly. The method used to work out how far they had travelled over a given time was, to use a system such as shown below. As shown the line was of a certain length and was knotted at regular

  intervals, when the anchor plate was thrown overboard it tended to stay dead in the water, like a sea anchor. As the line was paid out, they could calculate the distance travelled, thus explaining the meaning of knots when referring to the speed at which they had travelled over a given distance. From that exercise they could estimate very roughly their longitudinal position. This again was the reason why so many ships overran their distance and came to grief on the reefs and atolls of places like the Houtman Abrolhus Islands. Even at this stage the main means of navigation were charts derived from the Portuguese who had many years of sailing experience in the eastern seas. There were no soundings on these charts, only the simplest outlines of coasts with place names. It was the accompanying navigation notes, the accumulated experience of decades which were invaluable to the early navigators. The Dutch and the English closely guarded their secrets, this being the reason why the spread of knowledge was seriously impeded for 200 years or so. In the mid-18th century the situation improved greatly with English, Dutch and French hydrographers attaining a new level of accuracy and integrity. This was tempered by their own level of experience and knowledge, gained by constant discussion and exchange of information. Bearing in mind that ships navigators were unable to compute their exact position until the latter part or the century. By this time they were using the Davis Quadrant pictured below.

Using this apparatus it was possible to be able to get a rough estimate of your latitude. but it was not possible to work out the longitude to any useful degree of accuracy.

It was not until 1731 that a new scientific age emerged, with the introduction of the very different 'Hadley's Quadrant'. In skilled hands latitude could now be determined with a very great degree of accuracy. It was to be improved by Captain Campbell RN and emerged as a sextant, a forerunner of today's sextant.

Later Jesse Ramsden produced an instrument made of brass, a fraction of the size of Hadley's Quadrant without losing any of the precision. This used in conjunction with Mayer's lunar tables in 1767 enabled them to at last calculate the longitude to within 30' accuracy. These tables gave the distance of the sun and some bright stars from the moon for every 3 hours Greenwich time. But because the cost was high, officers kept on using the backstaff instead of the brass 'Hadley'. Later on, a hardwood version came about and gradually the backstaff faded into the background. It took another decade or so before the final step was realised which was to be the advent of the 'Chronometer', virtually 'time in a box', this being the result of a great deal of work and testing by the maker John Harrison and Lt. James Cook. There were not many in use for a long time, again because to the costs involved. Late in the 18th century Arnold & Earnshaw were making excellent instruments at a a very reasonable price. 

Above (right) is the hard wooden version of 'Hadley's Quadrant, and left is the beautifully engineered brass version which in principal has not changed that much to today's modern sextant.

Another instrument of early navigation was the magnetic compass (right), the Chinese had known about compasses for a very long time and found that by stroking a a piece of metal with a piece of lodestone it would become magnetised and pointed to the earths north pole, lining up with the earths magnetic field. This worked fine until shipbuilders began putting more and more metal and iron into their vessels, this meant that the compass would fluctuate away from true north as they knew it.

John Harrison (left) and another Englishman, Alexander Dalrymple were mainly the icing on the cake, Dalrymple who at age 15 began a lifetime of study of hydrography, his efforts  making the sea's safe for mariners. Losses of ships in certain area's prompted Dalrymple to suggest to the directors that an official hydrographer be appointed, a position which was offered and accepted by him in 1799. Between 1780 and 1808 when he died, he published between 10 and 80 charts a year. 

 To all these gentlemen we all owe a huge debt of gratitude for their perseverance and integrity in providing mariners down the centuries with increasing levels of safety at sea and the means to navigate around those sea's. The ocean is a wild, powerful force that should never be under estimated.