# What is the weakest point on a modern submarine? **URL:** \ **Category:** Factual Questions\ **Created:** [February 24, 2010, 4:54am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236 "2010-02-24T04:54:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Claude\_Remains](https://avatars.discourse-cdn.com/v4/letter/c/898d66/32.png) [@Claude\_Remains](https://boards.straightdope.com/u/Claude_Remains)\ **Post date:** [February 24, 2010, 4:54am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/1 "2010-02-24T04:54:08Z")
I’m guessing that ballast tanks, prop shafts and torpedo tubes are all very problematic. What about the hull in general? ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [February 24, 2010, 5:42am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/2 "2010-02-24T05:42:23Z")
I think you will find that where the hull has something pass through it is the weak point. ---
**Author:** ![Claude\_Remains](https://avatars.discourse-cdn.com/v4/letter/c/898d66/32.png) [@Claude\_Remains](https://boards.straightdope.com/u/Claude_Remains)\ **Post date:** [February 24, 2010, 5:55am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/3 "2010-02-24T05:55:31Z")
No kidding? wow. Dang, before I go I still am wondering about the point that is _THE WEAKEST._ ---
**Author:** ![Dereknocue67](https://avatars.discourse-cdn.com/v4/letter/d/6de8d8/32.png) [@Dereknocue67](https://boards.straightdope.com/u/Dereknocue67)\ **Post date:** [February 24, 2010, 9:19am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/4 "2010-02-24T09:19:44Z")
Usually, when something tragic occurs, an official military investigation concludes the weakest point was the captain. ---
**Author:** ![Kiber](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kiber/32/317_2.png) [@Kiber](https://boards.straightdope.com/u/Kiber)\ **Post date:** [February 24, 2010, 1:56pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/5 "2010-02-24T13:56:38Z")
Possibly, it would help if you define what type of modern submarine you are talking about - as the weakest point will be different. For example - on a submarine like [this](http://www.lamorsubsea.com/files/sm300.jpg), I’m fairly certain the windows are the weakest point. By contrast - on a submarine like [this](http://www.armybase.us/wp-content/uploads/2009/05/australian-submarine-hmas-rankin-hull-6-and-us-navy-attack-submarine-uss-key-west-ssn-722.jpg), I’m fairly certain the weakest point is classified. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [February 24, 2010, 2:18pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/6 "2010-02-24T14:18:48Z")
> [@Claude\_Remains](#): > > I’m guessing that ballast tanks, prop shafts and torpedo tubes are all very problematic. Is there any significant history of serious failures of these on modern subs? I see no real reason why it would be especially challenging to design these to be as reliable as the rest of the sub. ---
**Author:** ![Icerigger](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/icerigger/32/432_2.png) [@Icerigger](https://boards.straightdope.com/u/Icerigger)\ **Post date:** [February 24, 2010, 2:39pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/7 "2010-02-24T14:39:40Z")
BTW on subs and ships as well how do they seal a spinning prop shaft from the sea. A surface ship can pump the leaking water out but a sub under high water pressure I would think any leak of water would be a disaster. ---
**Author:** ![smiling\_bandit](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@smiling\_bandit](https://boards.straightdope.com/u/smiling_bandit)\ **Post date:** [February 24, 2010, 2:44pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/8 "2010-02-24T14:44:07Z")
> [@Claude\_Remains](#): > > No kidding? wow. Dang, before I go I still am wondering about the point that is _THE WEAKEST._ Rick was being pretty stupid there, for some reason. Regardless, if we assume you’re talking about a modern naval submarine, there’s a real question of “Weak to what?” Are we talking something hitting it? Water pressure? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 24, 2010, 2:49pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/9 "2010-02-24T14:49:27Z")
> [@Icerigger](#): > > BTW on subs and ships as well how do they seal a spinning prop shaft from the sea. A surface ship can pump the leaking water out but a sub under high water pressure I would think any leak of water would be a disaster. High pressure shaft seals. [Here’s](http://www.emeraldinsight.com/10.1108/eb053372) a paper if you wish to purchase it. ---
**Author:** ![Bijou\_Drains](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bijou_drains/32/2814_2.png) [@Bijou\_Drains](https://boards.straightdope.com/u/Bijou_Drains)\ **Post date:** [February 24, 2010, 2:49pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/10 "2010-02-24T14:49:52Z")
How deep US subs can go is officially secret but I believe they say it’s below 800 feet. From what I have read once they go too deep the hull implodes. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 24, 2010, 2:55pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/11 "2010-02-24T14:55:17Z")
> [@Bijou\_Drains](#): > > How deep US subs can go is officially secret but I believe they say it’s below 800 feet. From what I have read once they go too deep the hull implodes. Can the limit be guesstimated from how thick a cylindrical steel hull could be before it couldn’t maintain positive buoyancy? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [February 24, 2010, 2:57pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/12 "2010-02-24T14:57:48Z")
_NCIS_ leads me to believe that the weakest point is a sonar operator with strong environmentalist leanings. ---
**Author:** ![Bijou\_Drains](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bijou_drains/32/2814_2.png) [@Bijou\_Drains](https://boards.straightdope.com/u/Bijou_Drains)\ **Post date:** [February 24, 2010, 2:58pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/13 "2010-02-24T14:58:51Z")
I would imagine people can make a good guess how deep the subs can go if they know how it’s built. I don’t know if the specs of the sub are secret as well, it’s logical they are also secret. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [February 24, 2010, 3:09pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/14 "2010-02-24T15:09:46Z")
> [@Kiber](#): > > By contrast - on a submarine like [this](http://www.armybase.us/wp-content/uploads/2009/05/australian-submarine-hmas-rankin-hull-6-and-us-navy-attack-submarine-uss-key-west-ssn-722.jpg), I’m fairly certain the weakest point is classified. Exactly. You’re not going to get any more detail than a generality like **Rick** posted. (And I don’t think his answer was stupid.) With respect to **Rick** ’s comment regarding hull penetrations, one of the principles of the U.S. Navy’s [SUBSAFE](http://en.wikipedia.org/wiki/SUBSAFE) program was a change in design philosophy to minimize the number of hull penetrations. Pre-SUBSAFE submarines had hundreds of hull penetrations, just like most surface ships do even today. Post-SUBSAFE submarines were designed with far fewer (but larger) hull penetrations that serve multiple purposes. In addition, the hull penetrations all have quick-closing emergency closures in the event of a pipe rupture inside the submarine (which is what sank the [USS Thresher](http://en.wikipedia.org/wiki/USS_Thresher_(SSN-593)), the loss of which was the impetus for the SUBSAFE program). > [@Icerigger](#): > > BTW on subs and ships as well how do they seal a spinning prop shaft from the sea. A surface ship can pump the leaking water out but a sub under high water pressure I would think any leak of water would be a disaster. You have shaft seals. Some nominal amount of water always does leak in, particularly at depth, but submarines have bilge pumps and drain pumps just like surface ships. ---
**Author:** ![Frank\_apisa](https://avatars.discourse-cdn.com/v4/letter/f/47e85d/32.png) [@Frank\_apisa](https://boards.straightdope.com/u/Frank_apisa)\ **Post date:** [February 24, 2010, 3:29pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/15 "2010-02-24T15:29:33Z")
Haven’t got the slightest idea of the correct answer to your question, Claude, but I just mentioned this thread in [a thread of my own](http://boards.straightdope.com/sdmb/showthread.php?p=12155979#post12155979)…and thought I’d give a link to it. Hope you stop by. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [February 24, 2010, 4:49pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/16 "2010-02-24T16:49:16Z")
Need answer fast? ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [February 25, 2010, 7:45am UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/17 "2010-02-25T07:45:38Z")
This might be a dumb question, but wouldn’t it make sense to power the prop electrically while isolating the motor-prop unit outside the hull, there-by not penetrating the hull with the shaft? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [February 25, 2010, 1:48pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/18 "2010-02-25T13:48:52Z")
> [@Shamozzle](#): > > wouldn’t it make sense to power the prop electrically while isolating the motor-prop unit outside the hull Wouldn’t this require either a motor that operates while surrounded by salt water, or one that must be pressurized (with air, or perhaps nitrogen) to match the water pressure? ---
**Author:** ![Kiber](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kiber/32/317_2.png) [@Kiber](https://boards.straightdope.com/u/Kiber)\ **Post date:** [February 25, 2010, 2:04pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/19 "2010-02-25T14:04:06Z")
> [@Xema](#): > > Wouldn’t this require either a motor that operates while surrounded by salt water, or one that must be pressurized (with air, or perhaps nitrogen) to match the water pressure? Plus - it would leave the only means of propulsion outside the pressure hall, making it pretty much impossible to maintain. And of course, it would still require a hole in the hull for power and control cables. So - several downsides, but not really any upside. ---
**Author:** ![yendis](https://avatars.discourse-cdn.com/v4/letter/y/ed8c4c/32.png) [@yendis](https://boards.straightdope.com/u/yendis)\ **Post date:** [February 25, 2010, 2:05pm UTC](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236/20 "2010-02-25T14:05:47Z")
> [@Shamozzle](#): > > This might be a dumb question, but wouldn’t it make sense to power the prop electrically while isolating the motor-prop unit outside the hull, there-by not penetrating the hull with the shaft? You use a podded system like [this](http://en.wikipedia.org/wiki/Azipod) where you have an electric motor in an external pod. Then you would only need to get electrical power to the motor. The problem with this system is that even the smallest amount of damage will completely disable the sub since repairing the motor while underwater would be difficult if not completely impossible. [Next page](https://boards.straightdope.com/t/what-is-the-weakest-point-on-a-modern-submarine/530236.md?page=2)