system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are some boats pointy on both ends, while other boats are pointy in the front and flat in the back?
gpt
The ideal high speed ship is infinitely long and infinitely skinny, this gives the least amount of drag but is impossible to build.

The practical high speed ship is fairly long and fairly skinny at the water line, but this also makes it relatively unstable.

A ship that is fairly wide relative to its length will be very stable; and make it a lot easier to put your stuff close to the water line which lets you carry more cargo with less of a risk of flipping over.

Ships that have a flat stern often aren't concerned about absolute speed, there is often something else they had to worry about more than just going fast.  It could be overall length like on a speed boat.  It could be a need to load cargo in from some side and a big rear loading ramp was convenient.  It could be that they're a big ass ferry only ever doing 6 knots so what do they care about high speed drag.

Points on both ends help the boat go faster with the same horsepower, but not all boats care about speed.