The Kamal was used by Arab sailors since ancient times. This
very simple instrument shares the same principle as the cross-staff,
and in fact may have been the immediate insiration for the development
of the navigational cross-staff. In the Kamal the cross piece
is replaced by a card, and the staff by a piece of cord.
Of course a cord does not lend itself to fine graduations,
and its design reflects the particular use of this instrument
and the circumstance of Arab navigators. The Kamal was not generally
used to find one's location at sea. Rather it was used to maintain
a particular latitude. That is, it was used to keep on course
by making sure a particular reference star remained at a specific
altitude above the Southern horizon at its meridian. Thus a Kamal
might have a series of knots on the cord corresponding to the
latitudes of specific destinations. In fact the destinations
might be written on the face of the Kamal for easy reference.
The Kamal was particularly well adapted to the common situation
of Arab sailors on the Indian ocean. For long journeys most sailing
would follow the monsoon winds, which blow steadily in either
an Easterly or Westerly direction for long periods. Thus one
sails before the wind with no tacking required. To find the next
port it is only necessary to keep at its latitude and you'll
run into it!
The Kamal can also be used for layout. A friend uses one
to measure off the distance for placing archery targets. He has
made a cord such that a six foot friend just walks away until
he matches the Kamal and the measurement is done. And the Kamal
is easily transported - just wrap the cord around the plate and
stick it in a pocket.
Kamal Cord Calibration
In making a Kamal one can determine the lengths to lay out
on the cord using the same procedures used for cross
staff graduation. The difference is at the Kamal cord is
traditionally marked out with knots instead of the marks on cross
staff staffs.
Making a Kamal
This Kamal was one of the projects for my 1998 workshop,
"Medieval Scientific and Philosophical Instruments."
Materials (provided at the workshop - illustration
below):
Wooden rectangle, 3/8" x 6" x 3", with hole
drilled in center (about 3/16").
Length of cord, about 24".
Construction:
Sand the board to remove splinters and to give a nice finish,
taking care not to change the length or width dimensions of the
board.
Thread one end of the cord through the central hole in the
board and knot it so it can not slip out.
Make additional knots in the cords at distances determined
to measure desired angles with either the 6" or 3"
dimension. You may use the table of
angles determined for the cross-staff, or either of the layout
boards described for the cross-staff to determine the appropriate
lengths.
Tie a knot at the end of the cord to keep it from fraying
and you are finished.
Medieval Science & Scientific
Instruments