The word kamal can be translated by “guide” or “road”, this is a very old navigation instrument, specially well adapted to take the height of the polar or other circumpolars stars. It was used by Arabic navigators at sea and on land (desert). Meanwhile, if its origin can’t be tracked with certitude, it is estimated around the X or XI century. It was discovered by occidental navigators during the “renaissance” period, it was mentioned by Vasco de Gama and other earlier Portuguese navigators in Indian ocean and red sea. Some of them even used it; it was named “tavoleta da india”.
This instrument was contemporary with the astrolabe and the quadrant.
Habit to use stars as celestial landmark and to take there altitude is much older. The most primitive of the instrument for this purpose is without contest the human body: The arm, extended or folded in front of the eyes, the hand, arm extended fingers closed or apart, foot etc... Thus, in the middle age, the finger thickness became unit of measure for the Arabic seafarer under the name of “issabah” (translation: finger.) This unit is found in all the Arabic treaties and navigation instruments of the period, the value is 1°36’.
The kamal came from another much more simple instrument call “wood” and he keep the Principe of this one. It is composed of 3 little sticks of wood (maximum angle measured 20°), The first one 3 time shorter then the third one, the second one twice higher than the first, ratio: 1/3, 2/3, 3/3. Each sticks where held by the upper part, arm extended, vertically, the base aligned with horizon, the upper part with star. The smaller stick for smaller angles, the second and the third for increasing angles.
Using the sticks
The kamal was also call “wood”. It was very efficient to measure relatively small angles, like the one found by Arabic seafarers, with pole star in equatorial regions. It consist of one, two or three small wooden rectangles (or square) from different sizes. Eventually, each rectangular board offer two ways to align the stars : one by the longuest side, one by the shorter side; in this case you find two small cord for each rectangle. Each board got a hole in its center where a string is inserted, traditionaly each string got 9 knots used as “scale”. The last knot (opposite to the board) can’t exceed arm length.
There is two way to use the instrument :
N°1, hold a knot between two fingers and put it at the eye corner and stretch the cord whit the other hand holding the board in front of the eye.
Cord towards the eye - small rectangle
idem large rectangle
N°2 (the most usual way) Holding a knot between teeth and stretch cord by holding the board in front of the eye
Cord between teeth - small rectangle
idem large rectangle
When the string is held by teeth or fingers with the board at such distance from the eye, that while the lower edge seems to touch the oceanic horizon, the upper edge just meets the star ( biting a different knot put the board further or closer from eye composing then smaller or bigger angles) the divisions or knots is then read off as the required latitude. On this example my kamal is graduated in degrees whit two board from 5° to 40° (or latitudes are higher here) to scale the string I used a tangent table. It is also possible to use the old traditional method to scale it, the one described by Mr Prinsep in the “Asian Cie journal of Calcutta” in December 1836: :
“Five time the length of the board is first taken (the one use for the measure in case of a rectangle) , as unit, and divided into twelve parts : then at the distance of six of these parts from the board, the first knot is made which is called “12”. Again the unit is divided into eleven parts, and six of these being measured on the string from the board as before, the second knot is tied and denominated “11”. The unit is thus successively divided into 10, 9, 8, 7, and 6 parts, when the knot tied will of course exactly meet the original point of five diameters: this point is numbered “6”. Beyond it one diameter of the board is laid off for the “5” division, and one and a half again beyond that for the “4” division, which usually terminates the scale.”
Grossel Grange about the Arabic navigation in the middle age where he reproduce, Al Magid and Sulayman al-Mahari navigations roads.
Arabic naval map from H.G.GRANGE
The most common celestial landmark used whit the kamal is the pole star, each knot of the string represent a certain number of issabah corresponding to latitude of the requested port. In fact they were often tying a knot after a direct observation of the star from the port they were leaving of and other one in the port they were coming to. To make it easier for the pilot the name of the port to reach was engrave on the corresponding board.
Whit the kamal help when you were reaching the port latitude the only think you had to do, was to sail east or west to arrive in this port. According to a period translation and a report by Mr Jomard: ”James Prinsep noted the correspondence between the knots (observed with the reference kamal) and different places often frequented by the Arabic seafarer. Thus, the first knot n°12 correspond to 22°38’ Calcutta’s latitude, the most northerly latitude for which the Maldives navigators have any occasion ; while the lowest knot, n°4, gives the latitude (nearly) of the southern point of Ceylon (actual sry lanka), or the average of the Maldives island.
The kamal can also be used as surveying instrument for measuring angles or calculate the “distance off” if the height of the landmark is known.
- James Prinsep : Notes on the nautical instruments of the arabs : Islamic geography volume 15
- Henri Georges Grange : Glossaire nautique arabe, ancien et moderne de l’océan Indien
- Jean José Ségeric : Histoire du point en mer
- Tony Crawley : Lo tech navigation
- Dennis Fisher : Altitude hooks and azimuth rings
- Richard A Paselk : Humbolt State University, the kamal
- Chronique Yemenite : Les poèmes nautiques de Sa’id Ibn Salim Bâtâgi’
- stratisc.org, André Niel : Y a-t-il une pensée navale Arabe
- Fun stuff for kids : Nabataea.net