How did water not get inside steamships from the “propeller’s holes”?

[Myth27]

Possibly a stupid question but ships had the steam rotating something inside and then I imagine some kind of long cylinder attached to this rotating thing piercing through the hull attached to the propellers outside

How come water didn’t go through this hole? Was it just perfectly made ? Did they had some kind of O-ring in the 19th century ?

[J-H]

You could ask the same question for modern screw-based propulsion.

It looks like it's a Propellor Shaft Seal on modern ships.

https://www.youtube.com/watch?v=79SqQgp92Mo
https://www.youtube.com/watch?v=UYqjuymZUGg

It's basically a stack of connectors, o-rings, etc. Pre-rubber you could use waxed leather or something similar for seals. Plenty of oil options (petroleum, whale oil, pig lard, etc.) for lubrication.

[Trafalgar]

You could ask the same question for modern screw-based propulsion.

It looks like it's a Propellor Shaft Seal on modern ships.

https://www.youtube.com/watch?v=79SqQgp92Mo
https://www.youtube.com/watch?v=UYqjuymZUGg

It's basically a stack of connectors, o-rings, etc. Pre-rubber you could use waxed leather or something similar for seals. Plenty of oil options (petroleum, whale oil, pig lard, etc.) for lubrication.

Both of these videos are for "dripless" shaft seals which have only been around for a few decades and are impossible without modern materials like stainless steel, synthetic rubbers, etc. The alternate system, which has been used as long as boats have had shafts penetrating the hull, is the stuffing box or packing gland. Essentially, you stuff the end of the hole with flax impregnated with a lubricant. The flax is compressed by a gland nut forming a seal against the shaft. The gland nut compression is adjusted to allow a small amount of water to enter the boat. This cools the packing material. So this system drips, usually the manufacturers want you to let it drip about one drop a second.

The problem with a stuffing box is over time, the flax wears out and the drip rate increases. You can tighten the gland nut to increase compression but you will eventually run out of threads and can't tighten it anymore. At that point, you have to replace the flax. This video shows how to repack a stuffing box.

[factotum]

It's worth noting that ships would often be expected to take on water over time, especially in the days of wooden vessels. They would usually be fitted with pumps so the water coming aboard could be removed (or else they'd just be bailed out in the case of smaller and older vessels). So, a little bit of a leak through the propeller shafts wouldn't be an issue.

[jayem]

Wikipedia explicitly mentions the need for a good "stern tube" and "stuffing box".

The early steamships were of course side paddle steamers with the holes above the water line. So it's mid Victorian engineering we're looking at.

It seems reasonable to me that some of the difficulties for the transition could be accounted for in this.
Looking at the picture for Smiths 1836 propeller it looks suspiciously like it's drive chain comes down from above
The Great Britain's crankshaft began at the top, and had a chain down to the propeller gear (I think that's mostly for fitting everything in. But it wouldn't have been hard to isolate it if they wanted. Though that's purely a guess, they also seem to have water cooled things so at some level they may have been splashing and pumping enough water around not to care about a bit more.)

That would then leave space for another steam-sub revolution, as improved tube technology allows a simpler engine design (corresponding with the engines being powerful enough for direct drive),

[farothel]

That's why older ships had bilges and bilge pumps. The water that dripped in would accumulate there and be pumped out.

[Myth27]

oh so water did drip in, intersting. Thank you for your answers :)

[Yora]

As the meme goes "That's the neat part, you don't!"

All ships get water inside the hull, and the propeller axle is one of the big reasons why. Making it a tight fit and a liberal use of grease helps, but at the end there's nothing to do but pump out that bilge water.

[factotum]

That's why older ships had bilges and bilge pumps. The water that dripped in would accumulate there and be pumped out.

Modern ships have them as well. It's practically impossible to keep all the water out--even if there are no leaks, water draining from the upper levels of the ship due to heavy seas or rain will likely end up at the bottom inside the hull and have to be pumped out. Pumping out bilge water is such a common practice they even have various rules and regulations about when and how you can do it, because by the time the water gets down there it's going to have all sorts of nasty stuff it's accumulated on the way down in it.

[Storm_Of_Snow]

Modern ships have them as well. It's practically impossible to keep all the water out--even if there are no leaks, water draining from the upper levels of the ship due to heavy seas or rain will likely end up at the bottom inside the hull and have to be pumped out. Pumping out bilge water is such a common practice they even have various rules and regulations about when and how you can do it, because by the time the water gets down there it's going to have all sorts of nasty stuff it's accumulated on the way down in it.

And things like condensation of water vapour from the crew breathing, steam from cooking and so on

But yes, as others have said, there are o-rings, bearings and so on around the prop shafts, but there'll be some seepage past them (and whatever lubricant you're using out in the water), and then it becomes something that's just part of the daily running of the vessel - to this line's fine, above that line you tell someone right now!, and below that line you're probably in dry dock

[Spacewolf]

Older ships used to use something called a lignum vitae stern tube. Which was basically just a wooden seal, as the water gets wet it expands and seals the shaft but has to be changed fairly often from my understanding.

Nowadays we use Simplex rubber seals which look like this https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

Or we use radial face seals which are basically what you'd sea on any type of pump to stop water coming up the driving shaft but on bigger scale, also called crane seals. Looks like this.
https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD

You shouldn't get any water past and if you do that's an issue especially if you are getting it into your stern tube room, on the simplex type sometimes you can get water coming back up the air line if it's not set up properly and you change from one ballast condition to another. But you really dont want it getting into your oil side as it'll mess up your stern tube bearings.

[Brother Oni]

Modern ships have them as well. It's practically impossible to keep all the water out--even if there are no leaks, water draining from the upper levels of the ship due to heavy seas or rain will likely end up at the bottom inside the hull and have to be pumped out. Pumping out bilge water is such a common practice they even have various rules and regulations about when and how you can do it, because by the time the water gets down there it's going to have all sorts of nasty stuff it's accumulated on the way down in it.

Hence the PG rated pirate insult, 'bilge rat'.