Back to Basics
I joined the Royal Navy as a Seaman officer in the late 70s and spent many a morning watch as a midshipman practicing the art of astronavigation. by definition, astro is normally used on passage not in coastal waters where different techniques for finding your way around safely are used. Using a combination of equipment - ship's chronometer (master timekeeper), deck watches (cheaper less accurate chronometers with known errors/drift that are calibrated to the ship's chronometer every day by the Navigator's Yeoman) and sextant can produce really quite accurate fixes. All calculations were done on sight reduction tables that reduced the maths to basic addition and subtraction thus eliminating the "complex" spherical trigonometry,RN junior officers were never regarded as intelligent enough to master that subject!. With practice, a good accurate fix +/- 5 miles (perfectly adequate for ocean passages) could be achieved in about 10 minutes. The only other long distance navigation aid available was Loran C and use of that was discouraged as the possibility of jamming could render it useless. It was drilled into us from day 1 that the "Mark 1 eyeball" method was the best, most reliable method as it couldn't be interfered with by any potential enemy. Just look up Captain Bligh's epic journey in an open boat in the Pacific, safe passage over 1000s of miles achieved by just observing the world around him at the time. Don't get me wrong, modern nav aids are very accurate and convenient but can't be relied upon when the shit hits the fan.