Kamal (navigation)

A kamal, often called simply khashaba (wood in Arabic),

Because Polaris is currently close to the celestial pole, its elevation is a good approximation of the latitude of the observer. The kamal consists of a rectangular wooden card about 2 by 1 inch (5.1 by 2.5 cm), to which a string with several equally spaced knots is attached through a hole in the middle of the card. The kamal is used by placing one end of the string in the teeth while the other end is held away from the body roughly parallel to the ground. The card is then moved along the string, positioned so the lower edge is even with the horizon, and the upper edge is occluding a target star, typically Polaris because its angle to the horizon does not change with longitude or time. The angle can then be measured by counting the number of knots from the teeth to the card, or a particular knot can be tied into the string if travelling to a known latitude.

arcsine

of the ratio of the width of the finger to the length of the arm. In Chinese navigation, the unit of jiao 角 is also used to represent a quarter 指 (an angle of 24 minutes 6 seconds).

Due to the limited width of the card, the kamal was only really useful for measuring Polaris in equatorial latitudes, where Polaris remains close to the horizon. This fact may explain why it was not common in Europe. For these higher-latitude needs somewhat more complex devices based on the same principle were used, notably the

cross-staff and backstaff

.

The kamal is still a tool recommended for use in sea kayaking.^[6] In such an application, it can be used for estimating distances to land. The distance can be calculated from the formula

${\displaystyle D={\frac {Sd}{s}}}$

where ${\displaystyle D}$ is the distance to the object, ${\displaystyle S}$ is the size of the object observed, ${\displaystyle d}$ is the distance from the kamal to the observer's eye, and ${\displaystyle s}$ is the size of the kamal.

Wikimedia Commons has media related to Kamal (navigation).

See also

• Sextant

Notes

1. ^ Al Salimi and Staples, A Maritime Lexicon, Hildesheim, Olms, 2019, 398.
2. ^ ^{a b} (McGrail 2004, p. 316)
3. ^ ^{a b} (McGrail 2004, p. 393)
4. ^ (McGrail 2004, pp. 85–6)
5. ISBN 978-81-317-0871-2
   , retrieved 10 September 2008
6. ISBN 1-56440-155-3

References

• Carreiro, Carlos B., Portugal's Golden Years, The Life and Times of Prince Henry "The Navigator". Dorrance Publishing Co., p. 84
• Malhão Pereira, J.M. (2003), "The Stellar Compass and the Kamal. An Interpretation of its Practical Use", in Proceedings of the International Seminar on Marine Archeology, Delhi, also published by Academia de Marinha (Lisbon, 2003).
• McGrail, Sean (2004), Boats of the World,
  ISBN 0-19-927186-0