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

Nobody has mentioned this, I’m surprised? Anyway seal leakage is a good thing. Spinning metal surfaces on metal surfaces is called machining and not a good thing. So you want some leakage around the shaft for lubrication.

In pharma applications we’ll use a barrier fluid. Pressurize it and even sterilize it. Those seals last a long time… But a simple lip seal like on a through hull prop shaft? Yep its designed to leak.