Just a note drillbabydrill, just speaking from my experience, a typical core barrel is 3m in length which can vary, but what doesn't vary is that they don't pull out of the hole every drilled core, a core barrel is usually dropped and retrieved inner tubular! This means they remain on bottom an retrieve the core barrel with what is called their Sand line, then a new barrel id simply dropped inside the drill pipe automatically latching it's self into the core bit and ready to drill another 3m. Just my experience!