"The only reason to pull up the entire rig is to change the bit. Core drills have to be pulled up more often to remove th contents of the hollow shafts."

Um, Uh, I do have to correct you as you are missing something. Present day core drilling varies very little from drilling for oil, at least in the sense of the actual drilling. The core is pulled internally on a very regular basis, whereas the entire string would only normally be pulled for bit changes/rod greasing in the same fashion as oil well drilling.

There are many, many other differences of course, but in this example they are very similar.

K

Best regards

K