There was about eight miles between the big semaphore towers and when you were at the top you were maybe a hundred and fifty feet above the plains. Sometimes, the clacksmen thought they could fly. It was like the illness known as 'calenture' that sailors experienced when, having been becalmed for weeks under a pitiless sun, they suddenly believed that the ship was surrounded by green fields and stepped overboard. He remembered it, because it was the only really interesting thing to happen for nine thousand years. One nearly hit Anghammarad, where he sat watching the ships drift by, far overhead. Sometimes an anchor drops, all the way to the dark, cold calmness of the abyssal plain, and disturbs the stillness of centuries by throwing up a cloud of silt. But the voyages still continue, aimlessly, with no harbour in sight, because there are currents under the ocean and so the dead ships with their skeleton crews sail on around the world, over sunken cities and between drowned mountains, until rot and shipworms eat them away and they disintegrate. Many still have crew, tangled in the rigging or lashed to the wheel.

Some stricken ships have rigging some even have sails. In short, it stops sinking and ends up floating on an underwater surface, beyond the reach of the storms but far above the ocean floor.

As a storm-tossed ship founders and sinks, therefore, it must reach a depth where the water below it is just viscous enough to stop its fall. And it is known that air is denser the lower you go and lighter the higher you fly. It runs: the sea is, after all, in many respects only a wetter form of air. The flotillas of the dead sailed around the world on underwater rivers.

Going postal pratchett