Hi all! I was reading something about maps and navigation, and couldn't help but wonder:
How did sailors navigate the vast oceans? They surely used compass for directions, and speed for distance. But how did they achieve such unbelievable accuracy? A deviation of 1° when stretched across oceans could lead to a place miles and miles away.
Secondly speed, how did they accurately measure speed on oceans?
And thirdly, if sailors got lost, how did they get their bearings with no idea where they are? How accurately could one know one's position from looking at the stars?
Navigation can be done with the stars, and the use of a sextant, which was in use from about 18th century onwards. This method can be very precise, but is reliant on clear skies. Navigation becomes super-precise when a clock that is powered by an internal spring mechanism is invented. This was John Harrison, in the 18th century. He made the marine chronometer. Up until then clocks had a pendulum. The pendulum could be affected by the three-dimensional movement of the ship, which would throw the mechanism off and make it inaccurate.
Prior to this, there was the backstaff, which is a reflecting instrument that could be used to determine the height of the sun or moon and angles and such (I am not sure of the exact method). The technique has a long history, and many variations, like the cross staff and the qudrant, but can be verified from the 17th century onwards. There is also the astrolabe (which also a long history), which is used to measure and calculate the position of celestial bodies. It was adapted to be used at sea from the 17th century onwards.
Ther are also different types of chart. Portlan charts are charts made by estimated distances between certain landmarks, rather than detailing the coastal topography. Experience was crucial factor in navigation, and when approaching a port or harbour a ship could expect to hire a local 'pilot', who had expert knowledge of that particular area, to navigate them through those waters.
Speed was be measured with a chip log. This is a board that is attached to a length of string on a reel, which has knots on it at regular intervals. The board is thrown overboard, the idea that is dragged behind as it resists the water. How much string is payed out in a certain amount of time while tell you how many knots per hour you are travelling.
There are many methods for navigation, and some are more accurate than others. Celestial navigation can be very accraute, but it would also depend on the quality of the instrument, the weather and the qaulity of your reference material - your star chart of sea chart. for a period, sea charts were very expensive and some were practically state secrets in the effort to keep certsin locations and trade routes from being exploited by rival nations.
Can you specify what you mean by "back in the day?" You referred to using a compass in your question. The compass had to be invented, and was not introduced to Europe until about the 14th century. Sailing, of course, significantly pre-dates that, and as far as I'm aware is actually a pre-historic practice.