Raising a Submarine 3

[idratherbefishing]

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.

 

[BigInch]

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

 

[msquared48]

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

 

[idratherbefishing]

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

 

[Zapster]

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.

 

[dcasto]

ping pong balls

 

[BigInch]

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

 

[sailoday28]

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?

 

[BigInch]

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

 

[quark]

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.

 

[idratherbefishing]

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?

 

[BigInch]

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

 

[gerhardl]

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?

 

[jmw]

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

http://www.ViscoAnalyser.com

 

[BigInch]

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"

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

 

[Zapster]

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.

 

[Sid7]

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.

 

[BigInch]

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

 

[Mr168]

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

 

[jmw]

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

http://www.ViscoAnalyser.com