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

There are several seals in line on the shaft. It leaks and there’s a catch-basin just below it, when it fills the water is pumped to a holding tank. Occasionally that water in the holding tank is pumped overboard.

The deeper the submarine is, the more the shaft leaks. Its not a bug, it’s a feature.