1. ASTRO-NAVIGATION OR NAUTICAL ASTRONOMY

Navigation is usually defined as that maritime art by which a mariner is able to get his vessel safely and expeditiously from one place to another. When within sight of identifiable objects or land, a navigator can establish his position and thus check his progress by two or more simultaneous bearings of shore objects, or by horizontal or vertical sextant angles of two or more shore objects. These methods comprise that branch of the subject known as Coastal navigation.

The early assumption of pre-knowledge in Navigation is that the student has studied and has practical experience of Coastal Navigation, understands navigational charts, the principals of position definition by Lat. and Longitude and by range and bearing, and the terrestrial methods of position fixing including the running fix.

Despite widespread amateur belief to the contrary, it is fundamentally no more difficult than coastal navigation, and indeed, there is less to learn than in coastal navigation. It does not involve any special mathematical knowledge to grasp its underlying theory and its practice does not call for calculations any more advanced than simple arithmetic, principally simple addition. It is true that the structure of Astro-navigation is held together by mathematics and it is the man that compiles the Navigation Tables and N.A.‘s who must be the mathematician, not the navigator, who merely uses them. There is nothing to prevent anyone with no more than a schoolboy’s knowledge of arithmetic and geometry from becoming a competent Astro-navigator.

A sextant is a simple instrument but the use of it requires a lot of practice. In the 1960’s, navigation reached a high level of accuracy because the technology was there (good instruments – daily radio signals – a stable platform aboard vessels) and because the will and interest of the seafarers were there as well.

In the Merchant Marine, no sextants were provided and a cadet/midshipman joining the fleet and wishing for promotion to 4th Mate had to work hard (10 hours/day) for six weeks to be able to acquire his own sextant. If he wished to discern the suspicion of approval in the eyes of his 1st Mate, he could not board with less than a Plath with a 6 x 30 telescope.

The day that his observations and calculations were good enough to be relied upon, he was ready for promotion. Some had the knack of it after a few months, some needed 6-8 months, and some still had problems a long time after this. The practice was all day long in his spare time, 10-12 shots in the morning or afternoon depending on his watch (watch was for working, not for practising). If he got the sympathy of the Officer of the Watch, they took sights together – the quickest way to find errors and learn from mistakes. Once the Sun was mastered, the boy spent every evening on the bridge shooting stars (cutting hours off his sleep)

The 3rd Mate took at least three Sun sights in his morning watch of 0800-1200; all Officers joined together for Noon; the 2nd took a last Sun around 1600; the Chief-Mate and 4th took a star at evening and at dawn. When you came on the bridge, the first sight you had was a battery of sextants, from three to five, ready for use. As in other trades before industrialisation, a very high level of skill and craftsmanship was achieved. The Sun was tracked between and behind clouds, the horizon between showers; a few seconds was enough to get a workable sight. The best Officers knew up to 70 stars; 30 stars were minimum.

Fig. 1-1. At Noon, when at least three Officers were observing, the senior officers always achieved the same results to within 1 min. Which means there was no, or negligible, personal error. The same could be said when more than one Officer took stars; they came to the same position within one sea mile.

A marine sextant should be heavy Plath, the telescope clean and adapted to the sight of the observer personal sextant. The way a person takes a sextant out of its box and keeps it in both hands will tell you who he is.  Most cadets had problems with technique:

Eyesight keeping (adapting telescope to the eye)  –  The way of kissing, light or too heavy.

Swinging body and sextant around spine, finding the vertical plane  –  Rocking the sextant to keep it vertical

Point’s ii and iii give big errors, i and iv very small ones.

Ship movements should have no influence on the quality of a sight. Rhythmic movements like rolling, pitching, heaving are compensated by the body – that is why they are seamen. Unexpected surging or yawing of the vessel can hamper and can make a sight very difficult; but then, so is reading and writing in such conditions. The wind can be a problem, but that is why a marine sextant should be heavy, having more inertia.

In hazy weather, the 2nd Officer took a sight on the main deck, as low as possible, and in many cases, a reasonable fix was obtained. Poor fixes were attributed to the poor horizon (dip), sometimes taking the Sun through clouds or in a flash between two clouds. However, the experienced Officer had a very good idea of the quality of his sight.

The best sights were between 30° and 60° above the horizon. Below 15° there were some doubts, below 10°, it was not worth taking. Above 80° you needed a minimum of experience and at 89°, correct Noon positions were always possible. The vertical edge of the horizon glass will give no clue as it will not be discernible. However, no Officer should have doubt about the verticality of his sextant; that is why the kiss should be light. Sights were rounded to 1.m, calculations to one mile. This precision is more than enough for ocean navigation, and closing a danger to less than five miles (ocean) is poor seamanship. Coastal navigation is a different thing.

Choosing the correct shades for both mirrors could make the difference between a good and a poor sight. Astro positions by sextant were very accurate – less than a mile out. This was proved over and over again by correct landfalls within less than six miles. Officers (and ratings) were proud of their trade, and sights and calculations were regularly compared and analysed. Job satisfaction was the result of the lengthy application.

Satellite navigation systems were the beginning of the end of the art; dead reckoning became sloppy, radio signals were forgotten, chronometers were not wound. It was also the end of sea-sense; currents and meteorology were no longer studied.

The coming of GPS put an end to it all. The sextant (one per ship) is hidden in a lower drawer; the chronometer is not connected to its battery. Time is given by the GPS. If one day the satellites should be switched off, 99% of the ships would be lost. In the 1960’s and 1970’s, a good ship had at least two mechanical chronometers. The top was taken daily at the same time, and they were compared with each other. Some ships had lamps in the chronometers to keep them at an even temperature. If one of them stopped working it was a major event, and the Master informed. The daily rate was quite correct. Later battery-operated chronometers became available. To the general surprise of all, they were no better; only one was provided. With the coming of GPS, the younger Officers took time from the set; some were using their wristwatch (Seiko), which was often steadier than the chronometer! Older Captains lost their health. Nowadays a 2nd Engineer can get a position by pushing a button.

The last three decades has seen a revolution in water transport of the same importance as during the demise of the sailing ship the change from steam tramp to cargo liners, which occurred in the 50s. It is another trade, another job. Let us hope the new seamen obtain the same level of satisfaction and pride as we had. Seven sights in five minutes were the norm. With the introduction of a Global Positioning System (GPS) of satellites, worldwide coverage of the Earth’s surface is now possible. The ability to fix a vessel’s position with great accuracy, even when out of sight of land, is now available. Highly sophisticated satellite fixing systems are no longer beyond the electrical resources of small craft or the financial resources of their owners. In this modern age, Astro-navigation is now carried out as a ‘back-up system’ on large commercial vessels. 

More often that not, it is the ‘small-craft’ navigator who is keeping the art of navigation alive through his interest and belief in his own efforts.