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Raising a Submarine
3

Raising a Submarine

Raising a Submarine

(OP)
A client of mine bought a submarine that was used for diving in and around the waters of Bermuda. The sub has been in-active for over 15 years and as such most of the electronics, pneumatic valves, and surface hatches have deteriorated over time.

The problem is this.

Due to vandalism the sub's main hatch was left open during a tropical storm and the vessel sank.

We have made initial dives on the sub to check all windows and main visible structure to make sure that this is intact.  We have also constructed form work inside the sub and sleeved one 4" Sch 40 PVC pipe and one 2" sch 40 PVC pipe through the main opening. We have then sealed both the openings with concrete.

The dry weight of the sub is 106 tons, it is mainly constructed of a 2" steel tube that is 52' long with 4' radius lexan hemispheres on either end.  It is currently sitting in 20' of salt water on a silt surface so about 3% of the sub is submerged into the silt.

We then used a 100 gal/min centrifugal pump to remove about 80% of the water from internal of the sub, allowing air back in through the 2" line.  

From speaking to various other people, some are recommending that I ignore the mass of the sub in my calculations.  I feel that I need to included it.  The goal is to get the sub to the surface and to make it secure so that it cannot sink again.

My other question is based on the "suction" that the silt bottom will have on the sub, and how best to proceed on calculating for the size of lift bags required to offset the suction.

Any and all comments are welcome as we are trying to derive the best plan forward.

We have considered using a barge to lift the sub, currently we do not have a crane that can lift that mass, nor is it in the client's current economic ability.
 

RE: Raising a Submarine

Made of 2" pipe???

LIFT weight = weight of sub material - weight of water displaced + weight of any volume of water remaining inside.

I believe the sub should have enough buoyancy to break from the bottom, if all water is removed.  Otherwise, if it ever found itself resting on the bottom during operations, it would be a deathtrap.

The size of the lift bags, as will the pressure required to fill them, will depend on their deployment depth where they are expected to begin lifting weight.  At 20ft the pressure needed to fill them will be 20 ft/33  * 14.7 psig (gage at surface) and you will need 1/64 ft3 for each 1 lbs of lift capacity required.  Lift capacity required must be calculated as was LIFT above, remembering that as more volume of sub is raised above the waterline, the volume displaced is less and less and LIFT weight eventually becomes the sub dry weight + internal water remaining as the keel clears the surface.

        IF YOU MUST DO THIS FGS BE CAREFUL !!!!

      THIS IS NOT NOT NOT NOT NOT NOT A JOB FOR
        AMATURES OF ANY LEVEL OF EXPERIENCE.

ESPECIALLY WITHOUT ALL PRECAUTIONARY, EMERGENCY AND BACKUP EQUIPMENT IMMEDIATELY AT HAND.  

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

If you are able to remove all the water from the interior, don't forget to blow the ballast tanks too if they are flooded.  If you cannot blow them, you will need external help to raise it.   

If the ballast tanks are not flooded, then just removing the water from the interior should be sufficient to raise it.   

Mike McCann
MMC Engineering

RE: Raising a Submarine

(OP)
BigInch,

Thanks for your response and confirmation on what calc's I am working with.  We have the local authorities standing by in all working situtions to ensure safty.

My main concern is the suction created by the silted bottom.
any thoughts on this?

"The only poeple who don't mess things up are those who don't do anything"
A wise old St David's Islander

RE: Raising a Submarine

Suction should not be significant problem if you don't rush the lift.  It took some time for the sub to sink into the silt, and the sub should lift from the silt once it is lighter than the water it displaces provided you give it some time.  It will take a while for the water to infiltrate the cavity that is created by the sub.  If you want to speed things up, use either an air lance or water lance to make some passages under the sub to promote paths for water to fill in under the sub as it rises.

RE: Raising a Submarine

ping pong balls

RE: Raising a Submarine

What's the crush depth of ping pong balls?

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

BigInch (Petroleum)  
In your statement

"LIFT weight = weight of sub material - weight of water displaced + weight of any volume of water remaining inside"
Aren't you considering  the "weight of water displaced"  as a positive bouyant force?  
If the vessel is so entrenched in mud, such that the hydrostatic pressure of surrounding sea water can not push up from the bottom, wouldn't this lead to a negative bouyant force?

RE: Raising a Submarine

Yes the weight of water remaining inside is countered by the same volume of water displaced, so of course algebraically cancel.  And, No. There is no negative buoyant force and there is no "suction".  Pore pressure inside the soil will equal the hydrostatic pressure of the water surrounding it.  

The proper term for "suction" is actually cohesion, which can develop between hull and the bottom, if the bottom is a silty clay or other material which has cohesion, a glue-like property.   

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

That requires a pontoon volume of 106 cu.mtr with dry weight of the submarine and more than 173cu.mtrs of air for emptying out. The vessel need not be pushed from bottom as the hydrostatic pressure does that on pontoons.

I knew about two accidents not because of wrong calculations but due to the rope breakage. One was not very serious but in the other accindent one engineer was crushed to death (he was standing on a barge nearer to the operation and supervising it). Just be careful.

RE: Raising a Submarine

(OP)
Zapster,

We are not planning to rush the lift, nor do we wish to leave the sub in a boyant state whilst we await for the cohesion to let go.  I am looking for a rough guess on how long this process would take.
Obviously the more lift differential that we give the sub the faster the result.  We can calculate the amout of lift we can apply, hard to figure out what is required. We were looking at a 5% differential to the total lift required.

What are your thoughts?

 

RE: Raising a Submarine

With only 5% + buoyancy, it might not happen at all.   Cohesion doesn't let go with time, only with force, or a water jet to cut the soil below.  Do a pull up test on a small flat plat stuck to the bottom, or get a bttom sample and check the cohesive value of the soil.  Is it silty clay?   

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine



What happens if there is a cohesion and an excessive lifting force? Can the sub suddenly gain movement, accelerate and 'pop' forcibly up to the surface? Precautions needed?

RE: Raising a Submarine

The brute force approach would suggest creating enough buoyancy that the sub will pop free on its own.
Alternatively, how about trying a horizontal tow? applying a tow to the sub might enable it to slide through the mud and this might break the suction. One way to assist this is by creating a shock wave in the mud e.g. with a small explosive charge as used in seismic surveys and placed at a safe distance from the sub.

This way you need only calculate enough bouyancy to raise the sub as if it were not trapped in the mud and this would help create a controlled safe lift. Gerhardl's concern is the obvious one, I would have thought.

Another approach might be to apply asymmetric buoyancy at the beginning of the charging of the flotation devices. By alternating the balance between port and starboard flotation devices it might be possible to generate a rocking motion sufficient to help break the suction while still at a safe level of buoyancy.

JMW
www.ViscoAnalyser.com
 

RE: Raising a Submarine

Yes, they can rise up very quickly using a brute force method, since exterior pressure is reduced with depth the volume of the air bags increases, if closed and not equipped with spill-out valves, so that also increases buoyancy.  

- Ya. That's how they got the name "balistic submarines" smile

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

Forgive my ignorance but how/why did this discussion regarding suction turn to cohesion?   These are completely different issues.  No one knows how much mud/silt will stick to the sub (adhesion).  I like JMWs idea of the horizontal tow to break suction and to smear much of the mud/silt off the sub, adding to the control of the lift when the sub breaks free.  Back to the discussion of suction.
Definitions:
Cohesion---The state of cohering or sticking together, (physics) the intermolecular force that holds together the molecules in a solid or liquid.
Adhesion---The property of sticking together (as of glue and wood) or the joining of surfaces of different composition
Suction---A force over an area produced by a pressure difference
Cohesion does not create suction.  Suction is created on the sub while trying to lift the sub.  When one begins to lift the sub, the pressure under the sub decreases resulting in a dP that increased the force required to break the sub free.  Without outside help, the length of time to break the suction is dependent on the permeability of the mud/silt to allow water under the sub to equalize the pressure.  Note that with suction, as one pulls up on the sub, the mud/silt is pressed tighter against the sub by the deferential pressure resulting in lower permeability.  As such, the harder you pull may not result in breaking the sub free faster.
 

RE: Raising a Submarine

I liked jmw's idea of a horizontal tow and alternate option of lateral pull on the sub to disturb the sub settlement into the seabed material(unless this makes sub settle more into seabed!!)

Was wondering 52' length 8' Dia, 20'WD.

Wouldnt it help if only either end was to be lifted up first and then other one(with adis mentioned above for loosening the bond between the seabed matl and sub). So the 'popping' on the surface may be more controlled and lesser brute force? Just my opinion.
regards

Siddharth
These are my personal views/opinions and not of my employer's.

RE: Raising a Submarine

Whether you call it cohesion or adhesion, makes little difference.  Is it adhesion when the molecules are different and cohesion when the molecules are the same?

How do you propose that suction is developed?  Just how is the area of reduced pressure created?  No deformation is taking place (such as when you pull on a suction cup, rubber deforms, increases trapped volume and reduces pressure underneath).  Perhaps you are confusing adhesion between soil particles in layers below?  I don't see the pressure differential.  Please explain how reduced pressure is created between a rigid hull and the soil below, or soil layers below?

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

Out of curiosity, how close laterally is the sub to the dock/pier?   

RE: Raising a Submarine

Suction or not what it really relates to is the resistance of the mud to flow. and that it is difficult to get the water to flow in.

When investigating using vibrating fork density meters for mud density measurement (river muds; the US Corp of Engineers amongst others use density measurement and ultrasonics to determine navigability by towing a sensor array through the mud) we discovered that unless the mud were flowing relative to the sensor the sensor would quickly trend toward reporting the density of the carrier medium, water. This we decided,was because the vibrations caused the particles to be displaced leaving a layer of water around the sensor. This might work if you could vibrate the sub's hull sufficiently. But, probably not at all practicable at this scale.

On the other hand, mud is essentially shear thinning.
Hence if one were to set off a shock wave in the mud using some kind of seismic charge, the shear waves in the mud, at the right time, could allow it to flow more easily especially if combined with a horizontal tow (Sid7, I figured you wouldn't want to apply the tow until you had just enough positive buoyancy that the sub would lift slowly once the suction was broken hence if it does respond to a tow, it shouldn't sink).

A sequence of small seismic charges detonated as the critical buoyancy is reached might do something (old sailing ships would sometimes, when stuck in the mud, fire their cannon off to try and break the suction).

JMW
www.ViscoAnalyser.com
 

RE: Raising a Submarine

Firing the cannon promotes liquifaction of the soil, via the pressure pulse in the air being transmitted into the water and then through the soil via increases pore pressure.  The increased pore pressure forces the soil particles away from their normal interlocked position producing a temporary liquified soil-water mixture, which lasts until the increased pressure dissipates and returns to the normal hydrostatic level.  The same effect can be observed when rapidly hitting beach sand with a shovel; the sand is liquified by the increased pore pressure which actually forces some of the entrained water to the surface for few seconds. Earthquakes also are observed to produce the same effect in some waterlogged soils and are responsible for rapid and catastrophic collapses of structures built above, as all soil layer support is temporary lost.  Some buildings have been known to tilt towards areas easily liquified below their foundations and then freeze in a tilted position as the pore pressure reduces and the soil returns to a solid state.   

So... still no "suction" force.

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

(OP)
The sub is approximately 300 meters away from any sufficient land mass.

There is a possibility of the horizontal tow, we would not be permitted to use any kind of explosives due to the sensitive enviromental concerns.

I believe, for safty sake that it may make more sense to raise one end and then the other so that we can control the lift.  I am un aware how much silt is on the bottom. So thus unaware how deep the sub may sink into the bottom as we angle it.  

I would consider it unsafe to use a water knife in a silty condition with a structure that has not been maintained in over 15 years that has been sitting in a very corrosive/electrolosis based environment. Would a concrete vibrator work as well as the explosive? Or would this just create a local condition?
 

RE: Raising a Submarine

Wouldn't it also be more problematic to lift one end, given your concerns above?

A vibrator will work, if the soil is sensitive to liquifaction.  That sensitivity will also determine the extent of any area that can be liquified by a vibrator.   Unfortunately silty clays are not the most easily liquified types of soils.  High clean sand content works best. Hard silty clays will not liquify.

I have not failed. I've just found 10,000 ways that won't work."-Edison  "If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search.  I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

RE: Raising a Submarine

No problem. in the last 12 months I have raised 6 No 300 ton lock gates sunk and buried in silt. only 1/3 of the structures area above the silt. 1 gate leaf was in 30ft of water.
Use submersible air driven pumps (Ingersol are best), blank hatches with plate, fittings for air and discharge hoses welded to the plates so that you can operate the pumps feed & discharge through the blanking plates. Overpressure is avoided through increased discharge during pumping as expended air increases the internal pressure slightly.
Easy job, should not take more than a few hours to lift once the pumps, pipes and blanks are in place.

http://picasaweb.google.com/Marine.Civil.Engineer/MarineCivilEngineering#

RE: Raising a Submarine

Further to my previous post.

1. Suction will not be a problem, you will have enough displacement/lift to overcome the small amount of suction.
2. A controlled lift can be managed through controlling the pumps from the compressor feeds at the ball valves.
3. Ensure that you have sufficient mooring lines to stop the sub from breaking away as it surfaces.
4. Always handy to have a solid anchor on the bottom with sufficient line to allow the unit to raise to the surface. the anchor point weighing approx 3 to 5 ton will drag bottom and slow any breakaway as the sub broaches the surface.

See Photo's on my webpage and you will see the structures we have salvaged
  
 

RE: Raising a Submarine

I have some experience with a vaguely similar set up. We were demolishing / cutting up a mining processing facility that had been custom fabricated on a large barge in the south, floated  over the ocean into place in the north, and then completely backfilled around itself so it essentially became landlocked.  It was used like this for 25 years with all kinds of utility services pipes etc connecting the barge facilities to the main land mass.
 In order to ensure ensure zero vertical movement due to changes in tides, we  had permanent dewatering in place, effectively hydrostatically isolating the barge from the ocean.

As decommissioning / demolition started we ceased dewatering and as we started internal demolition, and an effective reduction in the weight of the facilty,  we started to notice a some very significant elevation changes as the tides dropped and rose.

As engineers we had some interesting discussions and differring thoughts as to how much  change in elevation we could expect.  We didnt do too much calculations but the net result was do not underestimate the forces that natural buoyancy can create.

Is there a practical reason why you cant remove all the water from inside the sub??  Less weight, more buoyancy,  the more likely she will be to pull herself slowly off the bottom and rise gradually to surface.  Although yes I could forsee a rapid rise if she let go suddenly.

 

RE: Raising a Submarine

Is there a practical reason why you cant remove all the water from inside the sub??  Less weight, more buoyancy,  the more likely she will be to pull herself slowly off the bottom and rise gradually to surface.  Although yes I could forsee a rapid rise if she let go suddenly.

20 feet at 0.445lbs per foot, no real pressure worries using my method. placement of the pumps could be critical though (Ie. fore and aft).
A horizontal lift is unlikely, and at that depth and with the length of the structure, she will probably porpoise out of the water slowly, bow or stern broaching while the other end stays on the bottom, hence the drag anchor.
Would love to see more details (drawings) and accurate dimensions and layout, I could give you a better Idea of lift then.

RE: Raising a Submarine

The hull with dimensions as given displaces 91.8 short tons of seawater, so just dewatering the hull is not going to lift it.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Raising a Submarine

>(New PostMikeHalloran (Mechanical)      
5 Oct 08 11:59
The hull with dimensions as given displaces 91.8 short tons of seawater, so just dewatering the hull is not going to lift it.)<

Then it isn't a submarine, it's an anchor.
If displacement < Gross tonnage, it never floated in the first place.

Think about it!

That's why I asked for Accurate dimensions so that I could work out the displacement.



Chris



 

http://picasaweb.google.com/Marine.Civil.Engineer/MarineCivilEngineeringDiving#

RE: Raising a Submarine

That's what I was trying to say.


 

Mike Halloran
Pembroke Pines, FL, USA

RE: Raising a Submarine

Hi! Mike.

So we are in agreement then.

He has his figures wrong, I'm a little dubious about the dimensions as well as the Approx 80% volume of water removed.
He really needs to post the prints for the sub (with Dimensions) so that a controlled lift can be calculated.
I do this sort of recovery several times a year (See my webpage) and as long as I can get a reasonable seal - less water coming in and less air going out than I'm pumping - I can float just about anything that has a + displacement factor.

Ah well, Off to cut some mass from a floating dam (that isn't) so that I can float it again.
Later - Chris  

http://picasaweb.google.com/Marine.Civil.Engineer/MarineCivilEngineeringDiving#

RE: Raising a Submarine

Is the sub a hull with an external ballast system.

I am of the same opinion as posted above. The sub was floating when before it filled with water, so if you remove the water it should float again unless it's ballast system is compromised.  
I have helped raise boats sunken at the dock, due to taking on water in foul weather, by using air bags until the gunwales clear, and the pumping out the remaining water. Float right up. Air bags only have to lift the weight of the boat - the boats component's actual physical displacement. The only problem we have is on boats that have a huge mass above the gunwales. they tend not to come up level.  

RE: Raising a Submarine

Doesn't matter. To control its buoyancy, a submarine has ballast tanks and trim tanks, that can be  filled with either water or air. When the sub is afloat, the ballast tanks are filled with air and the sub's overall density is less than that of the surrounding water. As the sub dives, the ballast tanks are flooded and the air in the sub's ballast tanks is vented until the sub's density is greater than the surrounding water. the sub becomes negatively buoyant and begins to sink.  The sub has movable fins called hydroplanes that control the angle dive. When the sub has it's ballast tanks flooded, the sub is only just negatively buoyant, Therefore the only way that evacuation of water from the sub would not lift it. is if the Ballast were flooded. as the sub sank due to hatches being left open, the ballast should not be flooded.
Unless:
1. ballast were deliberately opened
2. Ballast valves have leaked away air allowing water in (doubtful)
Compression of the air in the Ballast tanks due to depth at 20ft would not be sufficient to prevent positive buoyancy if the sub is evacuated of water. 20 ton of lift bag assistance would more than overcome it.    

http://picasaweb.google.com/Marine.Civil.Engineer/MarineCivilEngineeringDiving#

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