Single or double hull? Real subs

[southern or]

I've been debating with some friends, and this topic came up. I myself, prefer double hulls for that extra protection. Something about a single hull scares me. Any thoughts?

[Ralph --- SSBN 598]

Re: Single or double hull? Real subs

Look at cross sections of various submarines.
The idea of single or double hull is not what most think it is.
In the first submarines, the ballast tanks where inside the main pressure hull.
Pumping water in and out to change depth.

The modern submarine has a pressure hull and an outer hull.
The outer hull contains the ballast tanks and the water does not come inside the pressure hull.
(There are trim tanks inside the pressure hull)

The pressure hull usually has a thicker material and more and stronger frames
The outer hull is not exposed to the high pressures at depth because the outer hull is designed to be completely empty on the surface and completely flooded when submerged.



The outer hull is to streamline the boat for movement through the water and cover up external piping and other equipment that is in the water.

As for a single hull or double hull boat being safer ........ Well the pressure hull is stronger than the outer hull.
But on the double hull, if the outer hull is damaged ...... punctured, there is a good chance that that ballast tank will not hold air so trying to surface could be a serious issue.
To help limit this, there are several ballast tanks in pairs. A ballast tank is divided in to two sections.
Usually at the top and bottom. A right side and a left side with two vent valves that work together as a single operating unit.
If one side is damaged (won't hold air) the other still works unless the valve won't close.
But then there are several ballast tanks. Some forward and some aft. Some even in the middle.

[seawolfsailor]

Re: Single or double hull? Real subs

even on double hulled subs the ballast tanks do not run the length of the boat, only a few section forward and aft. on modern subs the ballast tanks are forward and aft of the pressure hull and it runs a constant diameter the length of the boat. now soviet cold war designs used full length double hulls as they built subs more like a battle tank to make up for the lack of technology..

sub trivia.. early subs used a double vent valve above the ballast tanks. one on the hull and one a riser. this was incase the boat suffered damage to the deck or superstructure you had a back up. double valve protection is very popular in submarines

[seawolfsailor]

Re: Single or double hull? Real subs

present us thinking is not to survive a torpedo hit but to avoid one.
subs used to have several water tight bulk heads to seal off compartments, now most have one or two and its on either side of the reactor.

soviet designs and use of titanium this lead to a redesign of torpedoes in the 1980s, the mk 48 adcap.

up till then you would exploded a torpedo below a target and break its back but it was found the soviet subs could survive this so this became a direct hit weapon with a shape charge explosive to break through the layers of hulls.

[southern or]

Re: Single or double hull? Real subs

Interesting. I thought the 48 was puncture blast torpedo? As in it penetrates the outer hull before detention.

I like the idea of multiple hulls I think because you have that shield to protect what is the living space. I'm just not sold on the idea of avoidance as a primary defense. Germany has proven that even tech for sale is getting more and more advanced, like the DM2A4 torpedo. Another thing to contend with is just going out to sea in the first place. How many times did subs "bump" into each other? Something that would always be on my mind is what happened to the USS San Fransisco when she hit a mountain.

Knowing the design of the OSCARIIs and the LA classes, the theory of a LA colliding with the Kursk just doesn't make sense. Your right in that the Oscars are tanks and between that double hull and pressure hull, the LA would have suffered serious if not catastrophic damage. Then again, during the cold war both sides went bump in the night and I'm sure we don't know about most of them.

Ralph, I have to ask, where did you get that picture? What boat is that?

Seawolfsailer, grate diagram.

I never really considered the ballast tanks, but thinking about it there are some pics of the WWII boats coming home with a list. Now I'm thinking about the movie 'Operation Petticoat.' I'm getting sidetracked, but despite being a comedy, some of the stuff in that movie actually did happen. A sub really did torpedo a truck, and there was a sub operating in red primary because a fire in port melted off the outer coat.

[JWLaRue]

Re: Single or double hull? Real subs

re: "LA colliding with the Kursk just doesn't make sense."

I'm not so sure about that. Remember that LA that ran into an underwater sea mount? Did quite a number on the bow sonar dome and its support structure, but if I recall correctly, minor damage to the forward pressure hull itself. (minor meaning that the boat survived)

-Jeff

[Ralph --- SSBN 598]

Re: Single or double hull? Real subs

I seem to have a knack for searching.

I use Google.
I type in what I am looking for. Sometimes I will move the words around.

This search is "submarine double hull"
Once the search comes up, I do not go through web sites.
I click on images.
Then I can see what is available.
https://www.google.com/search?q=submari ... 00&bih=732
Found the image I was looking for.
Click on image and when it is displayed, I can click on View Image or View Page.
I usually do both and make note or the url.
The image above came from http://wreckhunter.net/gal-u505.htm
The information was there.
The image is of the U-505.
The web page has lots of images of the 505 but this is the one that shows the free flood framing.

I find looking through images much easier and faster than reading through web pages looking for any thing.

[southern or]

Re: Single or double hull? Real subs

[quote]re]

The starboard side faired pretty well, but port side was smashed and breached those fore ballast tanks and flooded the forward compartments with fatalities.

By the looks of the starboard side, the hull crumpled.

(All photos USN)

[seawolfsailor]

Re: Single or double hull? Real subs

subs used to go bump in the night and you never heard about it, now its head line news.

when I arrived to sub school I went down to tour the scamp. on the pier was a smashed sonar dome off another boat. I asked about it. all I got was "these things happen".

I had to do a ballast tank inspection in drydock, second nastiest place on the boat. all kinds of stuff gets in there and tries to call it home

[JWLaRue]

Re: Single or double hull? Real subs

All things considered, that LA did quite well for a single hulled boat.

-Jeff

[seawolfsailor]

Re: Single or double hull? Real subs

All things considered, that LA did quite well for a single hulled boat.

-Jeff

she did hold up well. the damage never made it back to the "people tank", it used the ballast tanks like a big set of 5MPH car bumpers.

[JWLaRue]

<<Originally posted by "petn7">>

At the risk of possibly repeating some of the points already made, here is my understanding of single v. double hull subs:

Single hull advantages
- Minimum wetted surface for a given internal volume.
- Generally easier to build and maintain.

Single hull disadvantages
- Less protection against torpedoes, ice and debris.

Double hull advantages
- Greater protection of the pressure hull, whether it be from ice, impact, debris or torpedoes. This is one of the reasons why Russian/Soviet subs had double hulls. This is also the reason why I build double walled R/C Subs.

Double hull disadvantages
- Lesser internal volume for a given outer hull size
- More difficult to build and maintain. Recall that most Russian/Soviet subs have historically a higher ratio of time spent in port to time spent at sea when compared to American subs. (I can't recall the source of this fact)
- Generally have higher underwater drag due to free flood openings.

Source: Submarine Design and Development by Normal Friedman.

Note that a large portion of this analysis is comparing modern British/American nuclear subs with modern Soviet/Russian subs. There are obviously other design considerations that could negate a given advantage/disadvantage of a submarine hull design.

[JWLaRue]

<<Originally posted by "Covert Shores">>

There are a few submarine designs which have combined both double and single hull sections n order to accommodate unusual hull shapes, for example USS Halibut. And the 'wasp's waist' section of some special projects subs are double hulled for perhaps obvious reasons, starting with USS Seawolf SSN-575. The Russians use them in a similar way with cruise missile subs and also deep diving boats like Losharik.

We often hear how double hulls are defense against torpedoes. I think that that is overly optimistic. And the suggestion that they allow a submarine to go deeper is also a misunderstanding.

[JWLaRue]

<<Originally posted by "Southern Or">>

I liked the Halibut. Interesting design(s) with a huge list of specialty missions. As for the armor, I have to agree with that for most of the subs. I believe the Oscars have armored outer hulls, but that's an exception. SS-581 lives near me and she has a double hull. She also has two huge holes cut in her too.

[don prince]

"In the first submarines, the ballast tanks where inside the main pressure hull. Pumping water in and out to change depth."

I really believe the first subs (for example the U-Boat Type VII C) flooded the ballast tanks MBT1-MBT5; only the Main Ballast Tank MBT3 was within the pressure hull. At 8-10 meters they blew the Negative Buoyancy Tank because it was extremely difficult to blow it at great depths and it would require more HP air to do so. Its function was to break the surface when diving. However, once the ballast tanks were flooded, then they would have achieved neutral buoyancy. Now they used the hydroplanes to change depth with prop drive (not more or less water)...

Regards,
Don_