Many U.S. submarines actually do have a small motorized, retractable Secondary Propulsion Motor (SPM) colloquially referred to as the “outboard.” It is lowered into position and and rotated in different directions. It is used for close maneuvering situations (like docking).
USS Scorpion, an older Skipjack class “attack” sub, sank below crush depth in 1968.
Hmmm, yes maintenance would be a problem.
But besides that, I was thinking that the unit could be in its own sealed hull. Granted, the shaft would still need to be sealed, but a breach would only compromise the isolated hull and not the main hull.
As for power and control cables, would it be easier to seal these than a dynamic shaft? And couldn’t power and control be transmitted by induction through the hull, precluding the need to penetrate the hull? I’m reaching here, I know, but its just a thought.
But yea, the lack of maintenance access would be the deal killer.
A breach would almost certainly render the propulsion unit inoperable. While not as rapidly fatal as a breach to the main hull, this would be an extremely serious emergency that could threaten the sub’s survival.
Doing this efficiently through a thick metal hull looks to be extremely challenging.
Not to say that sealing a shaft against 80 atmospheres of pressure is trivial. But it has been done, and made reliable.
The shaft isn’t really hard to seal. About the only thing that would absolutely prevent you from stopping the water from coming in would be the entire shaft falling out. If that happens, you’ve got much, much bigger problems.
Speaking from intimate experience(I once spent a very long day scraping, cleaning, polishing, and painting one of the shaft seals on the enterprise)…
Pretty much there are 3 main systems keeping water out of the people space. For normal operations, there is a plain old(though very large) mechanical seal. If that fails, there is an even plainer old ring of packing, which can be tightened down to form a seal on the shaft.
If both of those fail, there is an inflatable bladder that seals the shaft. However, the shaft cannot be rotated if its inflated.
If worse comes to worse, and all of those fail, you would simply seal the hatch to the shaft room. Submarines may not have this last option, however. I’ve only been on one, and it didn’t… the shaft seal was in the engine room.
Right. Can’t do that on a submarine, because the shaft seals are in the engine room, which is one of just three watertight compartments on a Los Angeles-class submarine, for example (and the largest, BTW). If all of the shaft seals failed and you had uncontrolled flooding in the engine room, the sub is toast.
In my submarine, the shaft seal was, in fact, in a separate compartment from the engine room and, in fact, we did once have a leak and sealed just that compartment (with someone in it!).
Trivia: We did a Maximum Deep Dive Test before every patrol and someone would always tie a piece of string across the hull at max depth to impress the newbies when it broke as the sub went back to the surface.
Our max safe dive was 750ft but I believe modern subs can go 3x that. Our boat used to creak like hell at that depth. Pretty scary the first time.
In the movie “DAS BOOT”-the German U-Boat is portrayed in a very deep dive (the depth gauge reads in the “red” region). Finally, they hit the bottom-and the hull starts making all these scarey groaning noises (as the hull contracts under the great water pressure). Suddenly, there comes a series of sounds like pistol shots-and the chief of the boat explains that the sounds are of the rivets in the hull sheaing off, as the hull plates contract.
is this true? Seems like the next thing would be a wall of water flooding in!:eek:
I can testify to the scary groaning but I never witnessed rivets popping 
The screen doors.
Nope, not true. Like the exploding computers of the Entreprise’s bridge in Star Trek, it’s for effect on the viewer, added drama.
On a real boat, even a single rivet failing or valve/steam duct exploding would be a serious concern, esp. at 150m depth. Nevermind a whole lot of them at once. As you surmise, it means the end will come very suddenly, and very, very soon.
The groaning is real however (as has already been said), and it happened during any rapid change of depth, not just when you went too far down. It’s just the sound of the hull and bulkheads contracting/de-contracting in reaction to rapid pressure changes.
They did it the other way round in Up Periscope : the engineer tied a taut string to the walls of the engine room, to impress the newbies when it started sagging at the old boat went deeper and deeper.
Out of curiosity, what submarine (or class of submarine) were you on?
Even on a relatively modern submarine (like the Los Angeles-class I served on) the hull groans when making dramatic depth changes. Pretty unnerving the first time you hear it.
We also used to do the string trick.
The question needs to be clarified but as a point of impact I think the horizontal plane on the conning tower would be the weakest point of contact. Hit the end of one of those and you’re going to leverage it against the tower.
Can anyone tell me where the armor is thinnest on an M1A2 Abrams tank? Also, what is the frequency of the shield modulation on the USS Enterprise?
12.3 Megafonzies
HMS Revenge. A Polaris (SSBN) submarine.
Nice cutaway diagram of HMS Resolution (same class) at wikipedia.
It was only 25 years ago and it drives me mad that I can’t remember the names of the compartments and that I can’t find any annotated diagrams on the intertubes.
I want to say that the last compartment was the shaft room (but I might be misremembering). In another thread about submarines I claimed to work in the Sonar Instrument Space but I suspect that I misremembered that too. That’s what it was called on my previous (surface) ship. Any other Polaris submariners around who can help me?
It’s funny. I can remember exactly which compartment is which because one of the tests before you earned your dolphins was to go blindfolded from stern to stem (and point out all the fire extinguishers/breathing apparatus along the way) but I can’t remember the names. I suck.
I ask because it seems that a diesel-electric sub can settle down on the bottom, and be totally noiseless (unless a crew member drops a wrench).
Recently, I read about an advanced Swedish D-E boat (HMS Gotland) that gave the US Navy fits-it was so quiet that it couldn’t be tracked.
So, does the USN have anything to fear from non-nuclear subs?
My 2¢:
Yes and no. Modern diesel-electric subs are much better than anything available in WW2, and they’re as capable as nuclear subs in anything but powerplant. That is a big “but” however. Diesel-electrics don’t have the global range of nuclear, nor the ability to stay submerged indefinitely. As a secondary point, if they aren’t nuclear powered they probably aren’t going to be nuclear armed either. A carrier task force expecting trouble from below is going to be screened by robust anti-submarine defenses, including one or more hunter-killer subs, anti-sub destroyers and frigates, and air reconnaissance including helicopters deploying sonar buoys.
In short, diesel-electrics can be a cost-effective option for a navy of modest means and worth having, but they’re still minor league.
Voyage to the Bottom of the Sea suggests large humanoid monsters that pop up from behind a rock from time to time.
On re-reading, I see that you actually sealed a compartment with a leak with someone in it? Do you mean to say that they actually drowned? :eek:
(I remember a scene from the 1978 film Gray Lady Down, that I saw in the theater when I was 10 years old, in which a sailor was sealed in a flooding compartment. It completely freaked me out, which makes it all the more amazing that I went into the submarine service myself.)
We had to do the the much the same thing in the U.S. submarine force.
To be more precise, we had to wear an EAB (Emergency Air Breathing) device that hooked into various ports throughout the ship. Wearing a piece of black fabric over the faceplate (to simulate smoke), we had 3 minutes or so to make it from the torpedo room up forward, to shaft alley in the engineroom lower level back aft. You had to wear the mask the whole way, stopping to plug into air jacks as needed. Between stops to plug in and get a breath, you had to hold your breath. When you went through normally closed hatches, you also had to properly shut them behind you.