Eli5: How does water not get inside ships or submarines through the motor shaft?
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Its called a stuffing box. There are many different types, and all different kinds of applications. But the premise is: that the shaft goes through a (shaft sized hole) from inboard the boat, to the outside where the prop is. On the outboard side, theres a rubber bearing called the cutlass bearing that is usually rubber inside, and metal outside, and the shaft sits inside the rubber tube (imagine a condom, cut off at the end) and the rubber allows for vibration of the shaft from the propellar: dampening the vibration inboard that goes to the transmission, and the motor. Inboard: (as i said there are may types) but on the transom wall (where the shaft comes in the boat) there is usually a metal sleeve of some sort, that either bolts to the transom wall, or the shaft itself that covers the first part of where the shaft enters the boat (on its way to the transmission/engine) the types tat i have experience with, are the shaft sleeve type of stuffing box, where the shaft will come through the back of the boat, inboard: into this shaft sleeve, that has a coupler, a sleeve, and a locking nut… inside the sleeve, you put wax packing, which is just like it sounds. Its a piece of cloth that had been soaked in wax, and hardened into a square piece thats pliable: think like street chalk thats square… it comes in lots of different sizes… 1/4 inch 3/8 inch, 1/2 inch etc… so say that your shaft diameter is 1 1/2″ in diameter… your shaft sleeve/ coupler will be 1 5/8ths in diameter leaving an 1/8th of space around the outside of your shaft. This is where you stuff the packing into… then you tighten the coupler against the shaft tube, until it crushes this packing, and thus: stops the water… the reason they use wax though: is that you actually want a little bit of water to get theough the transom from outside the boat, to the inside. Because this is what lubricates the shaft, and reduces the friction of the thousands of revolutions per minute that the shaft spins… otherwise the shaft would heat up, and warp the metal, or ruin the engine through vibration. Then when you crunch the coupler to the sleeve, you take the locking nut, and snug it up to the coupler lip, so that it stays in place, and has the desired amount of lubrication (usually like a faucet with a single drip every 3 seconds or so!!)
Hope that helps!!
Cheers
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