NAP-Section

b) Early Navigational Instruments

"Morski Sviat" magazine, permission obtained

Other ancient orientation methods and tools were more sophisticated and elaborate. An example is the latitude hook - a pretty simple device but very useful and practical for its time. The Pacific peoples began sea exploration in about 800 A.D., travelling east into the Pacific and eventually settling many islands in the ocean. In their adventures, they sailed with canoes and used a few navigation devices at a time when most European seamen kept close to shore and rarely ventured into the open sea (with the exception of the Vikings who used a sundial for their ventures into the Atlantic ocean). The Pacific people used the latitude hook for sailing from one island to another, if both were on the same latitude. The navigational device consisted of two bamboo pieces. One of them was split, with a hook at the end. The other was a shorter bamboo stick (a pointer). The two were tied to one another at a right angle. The latitude hook worked because the stars appear to rotate around a fixed point in the sky - the celestial pole. In the northern hemisphere the celestial pole is Polaris - the North Star. At any given time at night the Polaris remained at approximately the same point in the sky. The latitude hook took advantage of this pointer and measured the angle between the Polaris and the horizon. The hook was held at arms length, aligning the pointer with the horizon. If the seaman could see Polaris through the hook of the perpendicular bamboo piece, he knew that he was keeping course in the same latitude in which he started his trip.
Another very simple device was used by the Arabs in their trade voyages around the Indian Ocean. Travelling in dhows (see History), the Arab mariners made use of a simple tool called "kamal" (meaning "guide"). The kamal consisted of a small wooden board with a hole drilled in the middle of it, and a knotted string that passed through the hole. The different lengths of knotted sting corresponded to different latitudes or certain key ports and way-points previously described by Arab seamen. It worked on the same principle as the latitude hook, but was more accurate since the string kept the board at a fixed distance from the navigator's eyes. The string was also what allowed this instrument to be used for a variety of latitudes, unlike the hook.
The "astrolabe" or "star-taker" -is a significantly more elaborate navigation tool and is said to be the first scientific instrument used for navigation. It is believed that the astrolabe originated in ancient Greece and was later "refined" by the Arabs into a more sophisticated device - highly artistic and ornamented. But the older and plainer astrolabe was the original tool. It was a disk with degrees of arc around its circumference and sight vanes on a rotating pointer called"alidade." The disk was most commonly made of brass and was vertically hung from a ring. The navigator would hold the device by that ring and raise it above his head. Then he would align the alidade, so that the star or planet he is measuring by, could be seen in a straight line - through both pinhole sights in the sight vanes. The angle of this line of view was then read by the alidade and converted into latitude.

"Morski Sviat" magazine, permission obtained

The quadrant is another instrument which seamen adapted for navigation. Its name comes from the quarter-circle that it uses as a scale. The simplest quadrants are made of a 90-degree protractor with a plumb weight hanging from its vertex. Astronomers were the ones who took full advantage of the instrument and the Arabs were, again, among the peoples who were quite familiar with the device. Instead of degree measures, some of the ancient quadrants had names of major ports written on the appropriate spots around the arc. When the cord hanging from the vertex cut the arc at the name of a certain place, the sailor knew that he had to turn east or west along that latitude line in order to reach that certain port. The readings of the quadrant were taken by two people - one to take the instrument and look at the celestial body of reference, and the other to read the altitude from the arc. In rough weather it was very hard to take a reading on this device since the instrument had to remain steady for an accurate reading. However this is slightly offset as in harsh weather visibility is usually poor and astronomical instruments couldn't be used in the first place.
In daylight times, navigators need to be able to orient themselves by the sun. The astronomical ring is yet another rather simple device, relying on the sun, rather than the stars, for its readings. It is simply a ring, as its name suggests. It consists of a circle hung from a ring. Gravity aligns the ring with the zenith (the highest point that the sun reaches in the sky). A tiny whole in the ring (pinnule) allows a ray of sunlight to shine onto the inside of the circle, which is graduated in a degree scale. Thus the sun's altitude is recorded; from that, latitude can be calculated.

The Vikings had no compasses or other accurate and complicated devices for navigation, but simply a variation of a sundial. They used these simple wooden instruments for their long open-sea voyages to Iceland, Greenland, and probably even as far as the North American continent. The sundial principle of keeping track of time remained the main type of "clock" (along with sandglasses) used on ships until the chronometer took over in the second half of the 1700s. The sundial was used to keep track of sailors' duty shifts, of celestial observations, and helped determine ships' speed. Later when clocks became available for ships to use aboard, sundials remained in use - to roughly check the accurateness of the other clocks on board.
An old, very complex, and highly accurate clock was the nocturnal. It was a star clock, meaning that it used the position of the stars to determine the phases of the moon, the lengths of days and nights, holidays, sunrises and sunsets, positions of the sun relative to the zodiac, and even (some advanced nocturnal) calculated tides. The first of these devices was developed in the 1200s and was used by Europeans as well as Arabs. The nocturnal consisted of a sight, a pointer, and date and hour disks. They were often crafted in brass and some were very elaborate. They remained the most accurate clocks at sea (and on land, for a long time). They were in use up until the beginning of the 19th century - long after the chronometer was perfected into a most accurate time keeping device. The only downside of the nocturnal was that it depended on the Polaris and could not function in the southern hemisphere (where Polaris was below the horizon) or in any other circumstances in which the star was not visible.

"Morski Sviat" magazine, permission obtained

Cross-staff

Back-staff

The cross-staff is a tool that was used for centuries as an astronomers' tool before the German mathematician and navigator Martin Behaim adapted it for celestial navigation in the 1480s. The cross-staff, or Jacob's staff, was a long, square rosewood or ebony staff, and a shorter crosspiece (transom), which slides up and down the staff. The staff functioned in the following way: it was placed close to the eye and the crosspiece was adjusted so as "to fill the apparent distance between Polaris or the sun and the horizon. Then, by the position of the crosspiece on the staff, an angular measurement was taken on the scale on the edge of the staff.

The first navigational instrument, whose creator's name is known for sure, was the backstaff. An English explorer of the 16th century, John Davis, was impressed by the cross-staff, but wanted to improve upon it, to avoid the error due to the "disorderly placing of the staff to the eye." His 1590 device (also known as the Davis or English quadrant) was so simple and accurate that it earned a place in navigation for over 200 years.

"Morski Sviat" magazine, permission obtained

Though simple in its application, the device is hard to describe. In just a few words though: it was made up of three vanes (sight, shadow, and horizon ) and a pair of arcs attached to a staff and divided in degrees. The sight vane slides along the sight arc just as the shadow vane slides along the shadow arc. The two arcs are part of two circles with a common center. That center is found on the horizon vane. The small arc measures 60 degrees and the large one - 30, thus providing a maximum zenith altitude of 90 degrees. In simpler terms, the backstaff was an improvement over the cross-staff, because it allowed the navigator to take the measurement standing with his back to the sun (hence the name) and using the sun's shadow. The glare from looking directly into the sun was thus avoided resulting in greater accuracy.
An instrument that everyone recognizes as the "ultimate" navigational tool is the compass. There are two main types of compasses - the magnetic compass, which is most widely known, and the gyrocompass. The common magnetic compass was in use as early as the 13th century, it uses one or more magnetic arrows pointing in direction to the North Pole, using earth's magnetic fields.The gyrocompass, on the other hand, is not affected by earth's magnetism. It uses a gyroscope which is a device whose axel aligns itself parallel with the north-south line - earth's rotation axis. Thus a gyrocompass always points north and is immune to any magnetism errors that a conventional magnetic compass may suffer.
The sextant is an instrument used to measure the angular distance between two objects. By calculating the angular elevation of the sun or other celestial bodies, a navigator can determine both his longitude and his latitude. The octant - the sextant's predecessor - was invented in 1973 in England and America, almost at the same time. In America Thomas Godfrey, associate of Benjamin Franklin, came up with the device. In Britain John Hadley made the discovery. The octant was a double-reflecting instrument using two mirrors. The sextant works on the same principle - superimposingthe images of the two objects, the distance between which is measured.

Octant

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