system
Given the following post, respond as if you're commenting on Reddit:
human
Those huge cargo ships and oil tankers have a really small anchor compared to the overall size of the ship. How does such a small anchor manage to keep the ship in place?
gpt
Holding at anchor is the chain. The chain is what is the part that actually keeps the ship in place. 

The anchor is only set to keep the chain from dragging around and will represent the circle that the ship will swing at while at anchor. 

Normal anchoring is done by setting the anchor, then playing out at least 3 to 5 times the depth of the water in chain. The chain is lying along the bottom and weighing down to hold the ship. For the ship to move it has to either drag the chain or lift it up. That is what keeps the ship from going anywhere. 

In a open area with tidal changes or wind shifts the ship will swing with the changes. But the anchor holds the center of the circle it can move in.  

You can actually anchor a ship and keep it from going too far with just chain. The issue is in strong winds the chain will drag and the ship will shift slowly.

As an experiment take about 20 feet of chain. lay it out in a long line and try and lift the chain from one end. It gets way heavier as you lift it higher and each link comes off the ground.  Additionally if you lay it out in a N/S arrangement and grab the north end and try and walk it to the south, the longer the chain the harder to drag. (another example. Every try and walk back to the hose spigot while dragging the hose after it was fully extended? The further you walk dragging the hose the heavier it gets. It only takes a relatively small weight to anchor the end once you include the weight of the chain.