Ancient astrolabes and their use

How was the ancient megalithic astrolabes used? What was the so called sunboats, did they really measure sun rising and sun setting.

I think i may have found an ancient hexagonal astrolabe, in Zohan Iran. Strange though it seem to mark out two eyebrows that i interpretate as sunboats one with 12 stones and one with 9.

The inner base is a quadrant surrounded by a hexagon with a bit peculiar alignment, could anyone explain the geometric purpose of divide the hexagon in 16 parts the way they did?

https://maps.google.se/maps?ll=33.42....panoramio.all

http://en.wikipedia.org/wiki/Sextant