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]

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

 

[idratherbefishing]

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?

 

[BigInch]

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

 

[DiverCivils]

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#

 

[DiverCivils]

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

 

[miningman]

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.

 

[DiverCivils]

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.

 

[DiverCivils]

Can't figure out how to edit the URL's I've posted. I've altered the address on my website since

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

 

[MikeHalloran]

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

 

[DiverCivils]

>(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#

 

[MikeHalloran]

That's what I was trying to say.




Mike Halloran
Pembroke Pines, FL, USA

 

[DiverCivils]

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#

 

[unclesyd]

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.

 

[DiverCivils]

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#