Deep Submergence Submarines

Good Answer (!) to lyn... and,

TO ALL NEW VIEWERS: Click-the-link and read the page that the link takes you to, before adding more blah-blah responses~

"logged-out"

I believe.

Most of the younger (and some older...) engineers do not figure out about the natural movement of structures in service. This is not a deffect, its a natural perception deviation because during our basic education we learn how to dimension and check things regarding mechanical strengh. What happens in most of the cases is that structures that are dimensioned for mechanical strengh, with all included safety factors, end to be stiff enough to the user do not note while in service.

But this case of the submarine is a good point. This is the natural material elastic behavior working. Another one? Aircrafts like the B-777 can observe wing tip movement in the order of the fuselage diameter and more in normal operation. Other aircrafts as well, bu, of course, they are more noticeable in larger ones. Add to this the elastic movement of the engines vibrating and trying to pop out of the pylons, and you have a cool show next time you are flying. Not to mention what happens when flaps, slats and spoilers are deployed... they really shake that huge aluminum beams and steel or titanium flap tracks!

May be also scary for the untrained eyes.

Ronseto,

I did ride some "Alpha" trials on the subs just prior to the first Tridents being launched. I had heard that rumor about the sagging wire, memory tells me that was the "37 class" we also had the Narwhal, NR1 and a couple of other oddballs being built at the same time. You folks down in Pascagoula were involved with building some of the class at the same time.

My memory of the first ("Alpha") trials was that if any such trial was attempted it was in the schedule and fully sanctioned because Rickover was on board. The indicator of a successful trial on a personal level was that you did not get to meet Rickover.

The objective of the first trial was basically to test all systems to full power or capacity. The first deep dive was half of test depth plus 100 feet. Test depth occurred on one of the other trials. The trials were incredibly busy.

If you want to play around with some numbers the Trident was about 565 feet long and 41 or 42 feet in diameter (numbers on that order), I have a hard time believing that the test depth would have been greater than 2000 feet (way high in my estimation), the hull plating was probably less than 2 inches thick, the frames (gussets) would have been sized in that range. So you are talking about 1000 PSI maximum force on this kind of structure.

The numbers I heard bandied about for the wire sag was in the range of 6 inches. Who knows. I personally think it would sag significantly.

We never had piano wire aboard, but braided cotton line noticably sags, and not justat sea trails and test depth.

i don't know for certain concerning fast attacks, but i suspect fast attacks are just like boomers, in that the hull cross section is not a circle, being noticably taller than it is wide.

With this in mind, it is easy to understand why a line stretched tight at the surface would sag when at depth.

Something far more amusing than watching a string sag, is applying silver nitrate to all the black rubber eyepeices on the periscopes in maneuvering as well as those in the engine room that allow sight into the reactor compartment.....

silver nitrate penetrates the skin, and remains colorless until it hits sunlight, at which time it turns black.... which leaves everyone looking like the dog in 'the little raskels' ....but they have no clue, until much later.....ooooh and it doesn't wash off,, it has to wear off.

Benbenben

Is this a pressure thing, or a temperature thing?

Compression would increase heat, while depth in the sea, from what I know would decrease temperature.

Since Subs don't go very fast friction may not be as great a factor, though it has to be one considering the size of the vehicle.

What is the primary factor for the sag on the wire, and how the hell do they know one way or the other, as I would expect expansion and contraction of the hull according to temp and depth.

Oh, I get it! Once the wire is stretched, it does not contract.

Temps fairly constant. The amount of hull compression would not heat the captive gasses that much. Over 40 feet a small amount of hull contraction would let the wire/string sag.

Never been on a sub, but I drank with a subber once and that's waht he said.

He also said everyone stank!

You only stink for people who don`t live on Diesel Boats (Subs), (or Cat Class Diesel Frigates!)....the ones that do live on them, do not notice that you smell of Diesel and sweat!!!

That is why I never placed my eye directly on the rubber eye cup when doing my reactor compartment inspections. Some other people have had that done to them and it is pretty funny especially they use both eyes on alternating viewings and they look like a racoon.

...the blessing was, you can't smell yourself, as the stench builds up slowly over the almost 3 months without surfacing... breathing recirculated farts.

but the relieving crew could certainly smell the off going crew. it is the smell of regret, boredom, dread. an odor like yellow toenails and motor oil...and something not at all natural....

that is what the offgoing crew looked like too. unatural. too happy to be leaving the boat. too pale and squintey becoming reaquainted with the sun, and permeated as everything else with the smell of inescapability.

benbenben

Hi Ronseto.

If I understand the issue here, let me share my thoughts.

I believe that the piano wire was used to measure the hull deformation in a very small scale. The electrical resistance of the wire will vary with its section, caused by the stretching tension variaton.

I imagine the wire is stretched before the submarine submerges and the electric resistance is measured in that state. Then, as pressure increases with depth and the hull starts deforming (it will deform, even though the deformation cannot be noticed by the human eye) the tension on the wire will decrease. This will cause its cross section area to increase, leading to a decrese in its electric resistance.

The wire properties must be previously known to correlate the wire length with its electrical resistance and to correctly measure the hull deformation.

Cheers,

RGO

We are discussing a sagging wire. A visually sagging wire. You are the first person to introduce the use of other than visual tests. Why?

Maybe I didn't understand the issue...

Read the first post. Then read my response #1.

Cheers!

I was on a fast attack, but never saw the trick demonstrated. I was told that it only worked on older subs with a single hull, not with the modern double-hulled boats.

Nevertheless, it's a trick that tends to overdramatize the effect. If you've got a cord 42 feet in length that deflects by 6 inches in the middle, then you have reduced the point-to-point straight line distance by about 1/7 of an inch.

A nice post later on about electrical resistance etc.

my question otherwise would be: how do they see the sag unless someone goes down to look at it?

Being in submarines for 8 1/2 years (Electronics Technician (Nuclear) 1st class), and being on a number of qualification, Alpha and Bravo Trials while working for Electric Boat the cotton line with a large nut was used to show the hull compression for the benefit of new crew members or new shipyard engineers underway for the first time. To see it accurately, the string has to be extremely taut. Personally, I believe that a little give is good considering that a very rigid tank would probably implode at a shallower depth that a flexible one. And you are correct, the decks are isolated from the hull. This is also true for equipment mounting. This is commonly called rafting and its primary job is sound isolation.

Thick walled vessels can be typically stressed up to 1% strain if a high strength material is used.

With low strength SS this may be down to 0.3%, with thin walled vessels and failure in buckling maybe much lower.

0.3% in circumference (in this direction more critical then lengthwise) the diameter will change also with 0.3%: no problem to see or to convert to an audible signal if prestressed wire is used. Wire (without pre-stress) and nut still simpler as more easy to detect.

RHABE

Let's do a rough check.

p = γz

σ = pd/2t where

Δ = σd/E = γzd²/2tE

where p = pressure at depth z

σ = stress in the cylinder wall of diameter d and thickness t

Δ = change in diameter due to pressure p

If γ = 62.5 pcf and z = 1000 feet then p = 62,500 psf.

If d = 15' and t = 2" then σ = 19,500 psi and Δ = 0.12" (about 1/8" reduction).

A piece of string 15' long stretched taut across the cylinder will shorten by about 0.12". Integrating the arc length of a catenary is tedious, so let us consider the sag if the string is deflected at midspan with two straight lines to the points of attachment. The half length is 7.5' or 90". The horizontal distance is reduced to 90 - 0.12/2 = 89.94". Using Pythagoras' Theorem, the sag at midpoint is 3.3".

Regarding a previous comments in this string, I am pretty certain the frames are circular and have pretty much always been that way. Otherwise they would fail at depth. And double-hulled boats; we don't have any in the USN, but the Russkies, that's another matter.

Russian submarines have double hulls due to having their battery banks outside the pressure hull. In this way the batteries act type of "reactive" armor in order to disapate the energy from a torpedo hit.

You're right. I didn't spend enough time on board to get to know the construction. Thanks for the polite correction.

The Russian subs have a double hull, but only the inner hull is a pressure hull. The outer hull is open to the sea. It might be more accurate to describe it as a single pressure hull with a free flooding second hull.

The string thing is cool, but I always thought putting a styrofoam cup with the dive date on it, putting it in the free flood area of the sail and seeing it reduced to half size after returning from way deep was coolder. At least the NR-1 would squish it down that much.

Scuse me, I meant Dolphin not NR-1. Bad brain (although the NR-1 does go waaaay deeper.

ronseto said "It seems incomprehensible to me that compression could be so severe on a cylindrical hull".

The strain in the steel is really not very large. The method of demonstrating it is key to this thread. A very small change in length of a string will cause a substantial droop, noticeable to the human eye.