system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If an anchor can keep a ship from floating away, how can the anchor be pulled back up?
gpt
Most of the work of the anchor is actually the heavy anchor chain.  It sits on the bottom for many feet as a long weight.  The anchor (at the end of the chain) just adds a little extra grab on the bottom so the anchor chain doesn't drag.

The amount of chain you put out is typically measured in terms of several times the depth so you can get enough chain sitting on the bottom.  In still current and air, 3:1 is ok.  In bad weather, 7:1 is better.  To bring up the anchor, you just pull up the chain and the ship moves to be directly above the actual anchor, which causes it to release from the bottom.