NavList:

Fancis,

You can use kamals for higher altitudes but the 1 centimeter per degree geometry isn't preserved on the meteric kamal. I draw the line at 12° where 1 cm per degree is good enough through the range.

Indian Ocean pilots didn't need declinations. Latitudes were marked by knots on a string  for their personal kamals. This would have been done during visits to trading ports as an apprentice under the guidance of an experienced pilot.

I'm sure Canopus was useful. The helmsman would have been able to steer by it with ease. Pilots would have been able to knot in the port of call based on the maximum altitude of Canopus as it passed the meridian.

Finding the exact moment of Canopus meridian passage for the trial was done by first using the 2102-D then a phone app CN sight reduction calculator. A few iterations gets the time for an azimuth of 180°.

Greg Rudzinski

From: Francis Upchurch
Date: 2016 Mar 18, 08:06 -0000

Thanks Greg,

Yes, I guess even 28˚ is too big for accurate kamal readings. I suppose the Arab/Indian traders were in lower latitudes.

Do you think they knew the declination of stars such as Canopus and could work out latitude from meridian passage measurement? How did you find the exact moment of the meridian passage?

Best wishes

Francis