# How does a diesl submarine engine "breathe?" **URL:** \ **Category:** Factual Questions\ **Created:** [October 13, 2008, 1:57pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709 "2008-10-13T13:57:14Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [October 13, 2008, 1:57pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/1 "2008-10-13T13:57:14Z")
I’m assuming they’re like any other engine and need to mix air with the fuel in order to work, so where does all the air come from? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 13, 2008, 1:59pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/2 "2008-10-13T13:59:34Z")
The Diesel engines are only run when surfaced, or else just submerged by means of a snorkel (or _Schnorkel_). The engines provide surface propulsion and charge the batteries. The subs run on batteries when they are submerged. ---
**Author:** ![UncleRojelio](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unclerojelio/32/3160_2.png) [@UncleRojelio](https://boards.straightdope.com/u/UncleRojelio)\ **Post date:** [October 13, 2008, 2:00pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/3 "2008-10-13T14:00:07Z")
> [@Inigo\_Montoya](#): > > I’m assuming they’re like any other engine and need to mix air with the fuel in order to work, so where does all the air come from? Subs typically run on the surface while using the engines. Sometimes they can cruise just under the surface using a snorkle. To dive they need to engage the electric motors running from batteries that were charged while running on the surface. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [October 13, 2008, 3:55pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/4 "2008-10-13T15:55:14Z")
And when the snorkel was covered by a wave, and the floating ball valve cut off the air flow temporarily, the crew could suffer ruptured eardrums as the diesels drew in the air already in the sub. ---
**Author:** ![Paul\_in\_Qatar](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)\ **Post date:** [October 13, 2008, 4:01pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/5 "2008-10-13T16:01:03Z")
It is worth noting that for some reason, the engines feed off the air in the crew compartment. So when you are running the diesels off the snorkel, you get a heck of a breeze in the crew compartment. If you have a fire on a sub, you surface and start the engines. They suck the smoke out so you can see what you’re doing. ---
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [October 13, 2008, 4:01pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/6 "2008-10-13T16:01:31Z")
> [@John\_DiFool](#): > > And when the snorkel was covered by a wave, and the floating ball valve cut off the air flow temporarily, the crew could suffer ruptured eardrums as the diesels drew in the air already in the sub. Why would the engine’s air intake be connected to the interior air space? ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [October 13, 2008, 4:04pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/7 "2008-10-13T16:04:03Z")
> [@Paul in Saudi](#): > > If you have a fire on a sub, you surface and start the engines. They did that in Alistair MacLean’s _Ice Station Zebra,_ so I was sure it was a crock. 🙂 ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [October 13, 2008, 4:04pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/8 "2008-10-13T16:04:46Z")
Less chance of the air flow being blocked or restricted. ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [October 13, 2008, 5:43pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/9 "2008-10-13T17:43:08Z")
The Swedes have an attack sub, the HMS _Gotland_, which uses tanks of liquid O2 to run the engines while underwater. They spent two years running circles around the US Navy off the West Coast as part of an ASW training program. > **[HSwMS Gotland (Gtd)](https://en.wikipedia.org/wiki/HMS_Gotland_(Gtd))** > > HSwMS Gotland (Gtd) is a defense submarine of the Swedish Navy. It was the first ship of the Gotland-class, which was the first operational submarine class in the world to use air-independent propulsion in the form of Stirling engines which use liquid oxygen and diesel as the propellant. > It was built by Kockums, launched in 1995, and subsequently commissioned in 1996. > In 2015, Sweden's Defense Material Administration (FMV) signed a contract with Saab Kockums which included a mid-life upgrade of... Surely, if war ever finally breaks out between the US and the Swedes, we’ll get a heck of a bloody nose. 😃 ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [October 13, 2008, 5:52pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/10 "2008-10-13T17:52:24Z")
> [@Raguleader](#): > > Surely, if war ever finally breaks out between the US and the Swedes, we’ll get a heck of a bloody nose. 😃 Yeah, we’d be borked, borked, borked.😃 ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [October 13, 2008, 6:20pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/11 "2008-10-13T18:20:37Z")
> [@runner pat](#): > > Yeah, we’d be borked, borked, borked.😃 [http://roflrazzi.files.wordpress.com/2008/10/beaker-oh-shit.jpg?w=500&h=374](http://roflrazzi.files.wordpress.com/2008/10/beaker-oh-shit.jpg?w=500&h=374) (maybe not work safe due to language) ---
**Author:** ![slaphead](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slaphead](https://boards.straightdope.com/u/slaphead)\ **Post date:** [October 13, 2008, 6:39pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/12 "2008-10-13T18:39:43Z")
> [@Raguleader](#): > > [HSwMS Gotland (Gtd) - Wikipedia](http://en.wikipedia.org/wiki/HMS_Gotland_(Gtd))) Fixed the linky for you. And damn, it must take a lot of faith in German/Swedish engineering to volunteer to be sealed in steel can underwater with a whole lotta LOX. Yeesh! ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [October 13, 2008, 7:01pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/13 "2008-10-13T19:01:35Z")
> [@](#): > > HMS Gotland was loaded onboard the Norwegian semi-submersible heavy-lift ship, MV Eide Transporter, on May 10, 2005, for a month-long voyage over the Atlantic Ocean What kind of weenies have their sub _ferried_ to it’s base of operations? 🙂 ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [October 13, 2008, 7:02pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/14 "2008-10-13T19:02:55Z")
> [@carnivorousplant](#): > > What kind of weenies have their sub _ferried_ to it’s base of operations? 🙂 Well, with fuel prices what they are, I wonder what kind of mileage that sub gets on its own? 😃 ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 13, 2008, 7:12pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/15 "2008-10-13T19:12:38Z")
> [@slaphead](#): > > And damn, it must take a lot of faith in German/Swedish engineering to volunteer to be sealed in steel can underwater with a whole lotta LOX. Yeesh! What about GRAVLAX? ---
**Author:** ![ShibbOleth](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@ShibbOleth](https://boards.straightdope.com/u/ShibbOleth)\ **Post date:** [October 13, 2008, 7:18pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/16 "2008-10-13T19:18:58Z")
> [@slaphead](#): > > … a whole lotta LOX. Yeesh! Sounds like a Led Zeppelin parody. ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [October 13, 2008, 8:26pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/17 "2008-10-13T20:26:55Z")
From what I’ve read about World War II US fleet submarines, there was a very large induction valve in the hull that was opened while running on the surface under diesel power. [http://www.maritime.org/fleetsub/chap7.htm](http://www.maritime.org/fleetsub/chap7.htm) ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [October 13, 2008, 9:43pm UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/18 "2008-10-13T21:43:37Z")
> [@WF\_Tomba](#): > > Why would the engine’s air intake be connected to the interior air space? The interior space acts as a “free” water separator. Sucking water into a diesel engine can be very destructive. Due to the high compression ratios, it doesn’t take much water to hydraulically lock the engine. Even without a complete hydraulic lock, the water can raise the compression enough that combustion pressures exceed design limits, blowing the head gaskets at best, or causing failure of the head bolts/studs at worst. Additionally, without using the hull volume, the snorkel would need to handle the peak induction flow rate with minimal head loss. With the large hull volume, it only needs to handle the average rate. Finally, since stealth is essential in sub operations, reducing the induction noise by any available methode is desireable. ---
**Author:** ![Booker57](https://avatars.discourse-cdn.com/v4/letter/b/b9e5f3/32.png) [@Booker57](https://boards.straightdope.com/u/Booker57)\ **Post date:** [October 14, 2008, 1:16am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/19 "2008-10-14T01:16:45Z")
> [@slaphead](#): > > Fixed the linky for you. And damn, it must take a lot of faith in German/Swedish engineering to volunteer to be sealed in steel can underwater with a whole lotta LOX. Yeesh! And no bagels or cream cheese! ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [October 14, 2008, 2:47am UTC](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709/20 "2008-10-14T02:47:37Z")
> [@Kevbo](#): > > The interior space acts as a “free” water separator. Sucking water into a diesel engine can be very destructive. Due to the high compression ratios, it doesn’t take much water to hydraulically lock the engine. Even without a complete hydraulic lock, the water can raise the compression enough that combustion pressures exceed design limits, blowing the head gaskets at best, or causing failure of the head bolts/studs at worst. > > Additionally, without using the hull volume, the snorkel would need to handle the peak induction flow rate with minimal head loss. With the large hull volume, it only needs to handle the average rate. > > Finally, since stealth is essential in sub operations, reducing the induction noise by any available methode is desireable. It also allows for continued engine operation when the snorkel head valve momentarily closes due to immersion by waves. The hull’s interior volume is used as a reservoir which the engine can draw on, creating a (hopefully) small vacuum until the valve re-opens. [Next page](https://boards.straightdope.com/t/how-does-a-diesl-submarine-engine-breathe/467709.md?page=2)