Would somebody please explain to me what happens to the exhaust from a submarine’s engine. I’m not talking about nuclear, that I get, but for a combustion engine that’s underwater I figure the exhaust has to go somewhere besides bubbling out the back (kind of defeats the whole stealth thing). And while you’re at it, since these engines must burn a whole lot of oxygen during combustion, where does this come from that the whole crew doesn’t suffocate in a matter of minutes?
There are two major types of submarines. Nukes, and 'Diesel-Electrics". A diesel electric boat uses electric motors powered by batteries while underwater and diesel engines for propulsion and to charge the batteries when surfaced.
Try typing “submarine” in your search engine.
Simple…they don’t run combustion engines while under water. They use batteries to power an electric engine. Diesel submarines surface to recharge the batteries by running the diesel engines making them vulnerable.
Your reason for why running a combustion engine underwater are on the mark which is why it doesn’t happen.
Diesel powered submarines can only run their main engines at periscope depth…((about 45’)).They get combustion air thru a snorkel device.The exhaust it sent overboard via a different part of the same “snorkel mast”. The engine is used only to charge the main storage batteries which power the ship when submerged.Main propulsion is a huge electric motor run on the batteries.
…missed by one freakin minute. I have to type faster next time!
… but that won’t stop me from crawling off on a tangent with a bullwhip in search of a dead horse. Without the electric motor, there would have been no really effective submarines. Previous attempts had relied on muscle-power to move the sub (the Turtle, of the American revolution fame, and certain Confederate submarines from the Civil War). These had the advantage of producing fairly innocous exhaust (stale breath) but obviously they still used oxygen and couldn’t move very far (or fast) underwater.
Electricity is the key. The Dutch began fitting schnorkels to their submarines in the 1930s, and everyone was doing it by the end of WWII.
Those wily Dutch. First with the wooden shoes, now with electric submarines… 
Yes, any moment now the Dutch will come up with yet another devastating advance in combat technology and thereby assert their rise to world dominance. My bet’s on the as-yet unexplored military applications of the windmill. The Germans stole that schnorkel thing right quick, but they just wouldn’t be able to stand looking silly with windmill war machines.
Actually, there was some experimentation by the Germans in the latter part of WWII, and the British after the war, of using hydrogen peroxide as an oxidizer that could be stored aboard the submarine and used to run the diesels underwater. The technology actually showed some promise before atomic power made it obsolete.
Actually,
since the Dutch Army is the only Unionized army in the world, imagine having to take a vote on whether to attack a machine gun nest…
Perhaps they think that they can get all the other Armies unionized too, then they wouldn’t be a threat to them, or anyone else.
Kevin
I was interested to find out recently just how many submarines in use today are still diesel/electrics. Not just because they’re old relics, either - there are some downsides to nuclear power, and diesels still get built.
Nukes are god-awfully expensive compared to diesels, and the battery technology today is a lot better than it was back in the 40’s. Whether or not nuclear power is worth it depends on what missions the sub will be called on to do.
The British navy in particular, I believe, has some nuclear subs but uses quite a number of top-of-the-line diesels, crewed by very skilled officers and men. I’m told that they make fearsome opponents, even when matched against nukes.
I’ve heard that diesel/electrics have one significant advantage over nukes, and that is the ability to completely shut down everything and go truly dead silent submerged. (Obviously, they can’t be moving.) Nuclear reactors still have to keep some amount of cooling water flowing.
Whether this is enough to be significant must be determined by somebody with more knowledge than I…
No it mustn’t. You explained it quite clearly. The problem in a diesel boat is that in order for (almost)EVERYTHING to be shut down, the boat has to be sitting on the bottom. That requires a sandy, level, relatively shallow seafloor. The boat can be pretty damned quiet doing that, but cannot hear very well. Obviously it can not go active with it’s sonar. So it can sit in ambush (waiting for a surface ship) for, say 8 hours before it has to head for the surface. But a US Los Angeles class attack boat can pass within a couple of miles of it without being heard.
And once the diesel boat makes any noise, it’s toast against a US ASW vessel.
I’ll quite happily admit that I know next to nothing about submarines, but: Why does a diesel-electric have to “sit still” to be more quiet than a nuclear sub? All other things being equal, the nuclear sub has reactor noise where the diesel-electric runs off nice & silent batteries, right ?
So if a diesel-electric sub is engineered as well as a nuclear sub, wouldn’t it be the quieter of the two, moving or not ?
S. Norman
I did not know the Dutch invented the submarine snorkels. Neither did I know we had the only unionized army in the world.
But tell me this: were all WWII submarines Diesels? I’d say so. Then what the hell is up with Das Boot? Surely, most of the scenes (there’s even a scene where the sub hits the bottom) are beyond periscope debt. Yet, the sub runs its diesels all the time, and I can’t recall any mention of electric power whatsoever. Is the movie inaccurate? It seems so well-researched in every other area.
So: did U-96 have an electrical backup that allowed it to dive deep, or were the depths in Das Boot exaggerated?
Hello Coldie.
Yup, U-96 was diesel-electric - and in the series/movie they did run on electrics quite often. It’s not really a “back-up”, it’s the only propulsion when below snorkel depth.
I seem to remember one scene where the crew is completely exhausted from a storm in the North Atlantic, forcing the them to dive and run on batteries for a while, just to get a chance to sleep for some hours. That scene - with almost the entire crew sleeping and no sounds but the humming of the electric engines - stroke me as one of the most eerie in the entire series.
Darn, now I’ve got to rent the movie.
Oh, and the Danish army is unionized as well, although not to the point of voting on the battlefield.
S. Norman
Thanks, Spiny. I love Das Boot as well - best German movie ever. Not that that in itself is an achievement 
Good to see your army is unionised as well. Sort of an easy logic: allowing the labour rights of guys with guns to be messed with? I think not! I guess that’s why there are so little revolutions in Denmark and Holland. The military are to busy debating the Christmas raise: 2.75%, or 3.00%?
Sorry for the hijcack, and we now return you to the cold waters of the North Atlantic, at periscope depth.
And I do know how to spell “highyak”, thank you very much.
An unrelated submarine question…
Are there any accounts of submarines capsizing and surviving? I would have to imagine that most (if not all) submarines are built with a low center of gravity so they are self-righting, but conceivably a collision or large enough wave might be able to flip one over.
I haven’t seen the movie in awhile but…
I thought they only ran the diesels when the were on the bottom and went straight up. So they only ran them for a little while, maybe? The exaust and oxygen would be a big problem. As far a depth I cant remember how deep they went. They were in the mediterrian sea, so it wasn’t ocean deep, correct?
As I understand it diesel/electric boats are deadly quiet. At least the ones built by the Brits are. Easily a match for any nuke sub out there as long as the boat has a decent charge on its batteries and that’s the rub.
Diesel boats have a very restricted time allowed underwater before they HAVE to surface to recharge their batteries. Even sitting still machinery to clean the air and run the computers and what not still suck electricity. The boat might be able to stay like that for a few days but sooner or later it MUST surface. Once on the surface a diesel sub is probably toast if anyone hunting it is nearby. In addition the diesel, when running, makes considerably more noise than a nuclear sub making the diesel much easier to catch.
A nuke sub can stay underwater pretty much indefinitely (8 years on a fresh reactor core?). Their only limit is food they carry with them. Even with the reactor pumps still functioning the are insanely quiet. At low speeds I believe they are quieter than the environment around them. Magnetic Anamoly Detectors (sophisticated metal detectors) are generally the best way to find a US nuclear sub that’s gone quiet unless you somehow manage to get REALLY close.
One other thing nuke subs have over diesel is a nuke sub is MUCH faster. In general they don’t go speeding about because that makes them noisy but they have the capability to haul ass should the need arise. Top speeds are classified but I’ve heard numbers in the 40mph range tossed about for US subs and a few who say that’s slow. The Russian Akula class attack submarine (nuke) supposedly could reach 60mph. Of course, when that sub was on trials in the North Sea American listening posts heard it as far away as the Carribbean. There’s always a trade off (the Akula could be reasonably quiet at low speeds).