Eli5: How does water not get inside ships or submarines through the motor shaft?

Question

Eli5: How does water not get inside ships or submarines through the motor shaft?

In: 112

Answer 1

It usually does, a little bit. There are all sorts of sources of water in a ship, and ships just pump it back out.

To minimize the leakage, ships use some sort of seal around the prop shaft. Historically this would have been something fibrous like rope soaked in oil, wrapped around the shaft and compressed.

More modern systems may use finely ground surfaces pressed closely together to make the water gap microscopic.