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samtor, thanks for your kind words. The deepsea vessel that can operate without support ship is a tool that is absolutly necessary if you consider that the daily operation cost of a support ship are around 80.000 USD / day.
So if you loose 70% of your expedition days to bad weather (as usual in such expeditions) the cost of deep sea investigation is just ridicoulusly high. This explains why we know more about the far side of the moon than about the deep sea of our own planet. (see TED talk Bob Ballard)

 
You might want to consider that if you have a pressure sphere of only 2 m you can not stay inside such a limited room for longer than a few hours. This limits the independence of the vessel you need a mothership where you can transfer the crew to have a meal, a shower, a bed.

The question how big a living space bubble must be to allow a crew to stay there for a month (what would be a good expedition time) was investigated by Grumman in the Ben Franklin Project. The answer: a living space bubble of some 100 cubic meter size is sufficient to host a crew of 4 with all their needs during a month with no mayor technical, social, biological, medical, problem to expect in total insulation. This is valid in the same way for deep sea submarines as for space stations.

Based on this fact i would consider a minimum size for a completly long term independent sub some 100 tons of displacement.

Concrete spheres can be made to stand average ocean depth of 4000m - so this would allow to have a boat that can reach about 90% of the ocean botton - except the extreme depths of the ocean trenches.

I talked with Carsten Standfuss of the Euronaut project about building a deep sea salvalge submarine that could work indenpendent of a Mothership based on these principles. We agree that it would be a double hull boat with a series of spheres. Something along the lines of Deep Quest - just bigger.

The reason why we are not yet all over such a project is most of all that we could not yet find the right financial partners to pull it off.

Wil

concretesubmarine.com

[video=http://www.ted.com/talks/robert_ballard_on_exploring_the_oceans.html]

will what would cause this?? im thinking salt?..but this is why im leary of using concrete...

those cracks are through the whole pillar...and its a standard mpa...

dough, i see you are very concerned about concrete in seawater. But trust me the experiences with floating concrete structures in the last decades made by oil / gas industy in the north sea has been EXCELLENT there is nothing to worry about.

Please check the following studies. (see here)

In short, damages on concrete structures - if any - happen in the "splash zone" this is where the structure experiments wet and dry cycles frequently. There is no damage if the structure is submerged permanently.

The foto of the bridge shows a damage caused probably by a combination of excessive use of thaw salt and poor concrete mix in the construction in first place.

Thaw salt damage and marine ambient are VERY different cases.

Cracks in concrete can have different origins and range from no problem to easy fix - to serious problem. Which is which needs differenciation. The most important thing is that the rebar does not get compromized.

The general picture is, if you see "appearant damage" by marine ambient on a "concrete structure" - you are probably looking at a structure made of faulty concrete mix  that never has been "concrete in in the sense of concrete engineering" in first place.

Well executed concrete stands in marine ambient for 200 years - with no sign of deterioration.

If the mix is faulty and the rebar inside starts to rust - what happens is, that the rust has 4 times the volume of the steel -  apart from tension resistance weakening due to steel loss, this process tears the piece apart from inside out due to the volume increase.

It makes little sense to think in "special covering" to avoid this - if the concrete mix is poor and faulty - the effects and damage will happen and be at plain sight in short time.

The good thing is - there is no hidden failure mode - if you mess it up you can see it clearly.

Hello Dough,

The legs of Troll A are not filled with water.

They had to hold the full water pressure of 350m depth (at mating process). And they are now under 303m hydostatic pressure since decades. The engineers of the fotos are standing at the bottom of the legs.

.

The legs have 24 m diameter and 1 m wallthickness. The structure was built in a floating building site - ballast water is in the cells of the base structure.

Check the slip form method (no one shot pour).

Dough, do i understand it right that you will have the lower part of the hull in fal to transport a light structure to the water - and then build with the method of "let form in place" on the water?

u-boatdreams wrote:

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Wil--in the paper- the scientific journal on the cylinder implosion. what is meant by a "cage" is this simply a layer of mesh?

would a 5 inch thick wall be too thin? i can go 6 inches tops for weight.

 

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The rebar cage refers to rebar in horizontal and vertical bars so that they form a cage there is no mesh involved - the mesh in ferrocement boats has a different function- it is to hold the mix in place while it is curing.

You must see wall thickness in relation to the hull diameter - Troll A has a hull diameter of 24 m and a wall thickness of 1m so you have a ratio of 1:24 - my hulls have a ratio of around 1:13.3 - this means that at the same depth the concrete in TROLL A is about twice as stressed as in my hull - means also that my hulls can reach about twice the depth of Troll A.

Most important is that the thickness/diameter ratio is sufficient to rule out buckling as expected failure mode.  So i would recommend to not go below the 1:24 of Troll A .

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The structure in the study below has a wall / diameter ratio of 1: 12,5 (24 cm wallthickness / 3 m diameter) very similar to my hulls.

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Paper Number 3011-MS
Title OCEAN IMPLOSION TEST OF CONCRETE (SEACON) CYLINDRICAL STRUCTURE
Authors Roy S. Highberg and Harvey H. Haynes, Civil Engineering Laboratory
Source

Offshore Technology Conference, 2-5 May , Houston, Texas
Copyright 1977. Offshore Technology Conference
Language English
Preview ABSTRACT

An ocean implosion test was conducted on a pressure-resistant concrete cylindrical structure to obtain the depth at implosion. The structure was a reinforced concrete cylinder with hemispherical end caps, twenty feet (6.1 m) in overall length, ten feet (3.05 m) in outside diameter, and 9.5 inches (241 mm) in wall thickness. The structure was near-neutrally buoyant having a positive buoyancy of 12,000 pounds (5.4 Mg) for a hull displacement of 85,000 pounds (38.5 Mg). The implosion depth of the cylinder was 4700 feet (1430 m). A predicted implosion depth, using an empirical design equation based upon past test results, was 16 percent less than the actual implosion depth.

INTRODUCTION

A pressure-resistant, reinforced concrete hull was constructed in 1971 as part of a Seafloor Construction Experiment, SEACON I. The structure was placed on the seafloor at a depth of 600 feet (180 m) for 10 months. Figure 1 shows the SEACON I hull prior to its ocean emplacement. Since its retrieval in 1972, it has been located in the open air about 150 ft. (50 m) from the ocean. In the summer of 1976, the structure was returned to the ocean for an ultimate load test, that is, the structure was lowered into the ocean until implosion.

SPECIMEN DESCRIPTION

The cylindrical structure was assembled from three precast, reinforced concrete sections. The straight cylinder section, 10.1 feet (3080 mm) in outside diameter by 10 feet (3050 mm) in length by 9.5 inches (241 mm) in wall thickness, was fabricated by United Concrete Pipe Corporation. The concrete hemisphere end-closures, 10.1 feet (3080 mm) in outside diameter by 9.5 inches (241 mm) in wall thickness, were fabricated in-house. Tolerances on the sections conformed to concrete pipe standards of not to exceed to ±0.75 inch (19 mm) for the inside diameter or minus 0.5 inch (13 mm) for the wall thickness.

Steel reinforcement in the amount of 0.70% by area was used in both the axial and hoop direction. Reinforcing bars of 0.6 inch (15 mm) diameter were employed throughout the structure. A double circular reinforcement cage was fabricated for each precast section; the concrete cover on the outside and inside reinforcing cage was 1 inch (25 mm). For the cylinder section, hoop rebars had a spacing of 27.25 inches (692 nm) and 31.25 inches (794 mm) for the inside and outside cages respectively.

The hemispherical end-closures were bonded to the cylinder section with an epoxy adhesive, no other attachment besides the epoxy bond was employed (Figure 2). The gap between the mating surfaces of the hemisphere and the cylinder was less than 0.13 inch (3 mm) for 75% of the contact area. Prior to epoxy bonding, the concrete surfaces were prepared by sandblasting and washing with acetone.

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Dough, i am not sure if i understand your project properly. Is the V shape supposed to hold external pressure or is it just a streamlined fairing in a 2 hull concept?

The steel itself in the tank collapsing in buckling failure has a pressure resistance of 40.000 psi -  this does not prevent the buckling failure at less than 10m depth.

What is important is not the compression strength of the material it is the compression strenght of the structure.

Anything that is not working in arch mode and fails in buckling will fail long long before the compressive strenght of the material is reached.

V or U frames can only hold a few meters of hydrostatic pressure - so you can use them for a pressure equalized fairing - but not for the pressure hull.

Frame design is for steel hulls - consider that the steel between the frames is in tension. The hull gets the aspect of a "hungry horse" under pressure, tensioning the skin over the ribbs.

Failure comes from welding failing under the tension load between frames - or frames failing under compression buckling out.

What comes first depends on the design (amount of ribbs) and quality of the welding. The predictibility of failure is difficult as it depends on many factors - being the compression strength of the material the less significative.

FAL seems to be a material that can be built to the necessary properties. But you should be aware that you are completly on new ground when doing so.

So a prudent way to tackle the matter would be having the hull tested 1:3 unmanned to see if the concept works.

Also be aware of possible fatigue processes as they happen in steel.

To stay at the safe side you should repeate the 1:3 test dive frequently.

. navantia shipyard - steel frame construcction scorpene submarine -

wouldnt youngs modulus work compared to steel or cement?

yes true uncharted territory but it has to start somewhere--

ill do a drop test first...if it holds at 600-700 ft--itll be safe at 200 my operation depth.

sure wil i undertsand that--when you speak of your subs as not worrying about buckling--taking the buckling element out because of the thickness--you are saying then i guess-that your hulls are built to a high saftey factor?

the problem using the catenary as an example is that forces under water act equally  at all points of the sub- compressing the hull at all points -this is why a sphere is the strongest shape...in those examples there is an unequal force apllied to just one block in the series--this creates a imbalance on the arch... this would not happen at depth--it would simply implode in all directions...

Wil--those would be extreme cases in a well built sub...one thing i learned was that when you have a pressure hull what you need to have is""stability" condition- fer-lite-concrete and steel all have good stability conditions...something called creep/rupture formations...

this is axially applied loads to the walls of the pressure vessel from the exterior-such as in the case of water pressure......ive been reading up on this a bit-

how did you make your prop?? i can size a prop for a boat but how do you size one properly for a sub--??

http://www.youtube.com/watch?v=HLnV-fdf9kQ

prestressed concrete...

Wil--thanks for that great explanaiton--on a boat i knew about prop aperture-however- there is a relationship to displacement and prop size..but of course on the sub you can use huge props..the skipjack had a 14 ft dia prop...

http://aqua-base.co.uk/concrete.html

CONCRETE
Life expectancy: up to 100 years or more
Condensation: none.
Initial cost: 7-8% more than steel, but greater economies of scale for multiple hulls.
Ongoing maintenance cost: much less than steel
Reduced down-time due to less frequent inspection
Excellent fatigue life
Good impact resistance
High mass moment of inertia and low centre of gravity means good station keeping behaviour and reduced motions
Slower thermal response/better insulation
Resistance to fatigue and crack propagation
STEEL
Life expectancy: up to 30 years
Condensation corrodes hull from inside
Initial cost: 7-8% less than concrete; traditional engineering and construction, fabrication in existing shipyards
Ongoing maintenance cost: much higher than concrete
Greater down-time due to more frequent inspection
More steel designers and fabricators are available

Aqua-base is doing bases for floating housing - we have a discussion section about floating real estate and surface floating solutions (here).

As far as i can see from their website they do a kind of laminated ferro method.

Your FAL material and method is something similar.

Those building methods are very different from cast reinforced concrete building as done in classic engineering.

So their "compare to steel figures" are probably not valid for a submarine hull that is built in cast (their figure says 8% more expensive)

We calculate that a concrete hull as we have built it in our pilot projects is ten times less expensive than a compareable steel hull - just for the building of the hull.

It is important to compare apples with apples - so you should avoid to compare a light frame hull with a massive shell hull.

A massive shell has a destruction depth horizont of 1400m - a light steel frame hull will not stand half of this. Compare only hulls that are built for the same design depth and contain the same amount of material.

Also to make steel last 30 years you have to run a maintenance shedule that is extremly expensive - and it includes drydock stays that can be as expensive as building the hull in first place - a concrete hull is 100 years maintenance free and deterioration free - that marks a enourmous difference in favor of concrete.

So if you break it down in cost per year of service life a cost difference factor of at least 10 or more in favor of concrete emerges.

We have built hulls at a total project cost of 455 USD / ton of structure ready built.

Just the cost of steel structure is between 3000 and 5000 USD/ton.

This is already a factor 10 - just for building it.

If you calculate building cost plus maintenance cost divided by service years - you get something between well above factor 10 or multiples of factor 10 - depending on your calcs - for the cost difference calculation.

 Picture from aqua-base gallery section:

The calculation steel vs concrete that aquabase is doing, may well be correct for their building method. If you check the picture above you see a lot of man with buckets of concrete and you see thin layers of fresh concrete. I assume that they have mesh wire sceletons that are filled with cement matrix - quality mesh wire is expensive, work is also expensive, the correct curing of thin layers of concrete is delicate, complicated, and therefore expensive too. So for THEIR specific building method 7-8% more expensive than steel might well apply.

I can see the plan of your sub. - looks nice. Do i see downlooking viewports?

Peter Madsdens Kraka is no longer in service,  Peter has biuilt a bigger sub yacht called Nautilus. (UC 3) - steel in marine conditions can be gone in a few months when the protection fails -  keeping protection by paint combined with anodic protection working is incredible expensive and a permanent struggle.

Like Peter many owners of steel ships decide to just let it go and not pay any longer. Especially a classic submarine littered with small spaces impossible to maintain, sandblast, and access is a preprogrammed quick victim for corrosion.

. 

There are many good reasons to build in steel - you can find know how for steel welding and building in every mechanic shop, you can find steelplating easy, you can get a hull together without building a form, you will have less questioning on the concept - steel hulls are a fairly common and widley understood by mainstream shipbuilding.

I don't see it as an error that Peter built in steel again, he is simply a steel man, educated in steel building skills, so he is making his subs with what he has on hand and is familiar with. There is nothing wrong about that.

Like with every material and technique there are up and downsides.

Wil

doug, i would be careful with "cost analysis" sent from somebody else, made for a project of unclear parameters.

The best way to do cost analysis is always to have clear that you need to think in "total project cost" - a project does never consist in 3 items you sum up and get a figure, a project always has "tousands of items" that sum up.

So the most important cost account is always the "other cost" account which contains the thousands of items that are not material cost. The most tricky part is to estimate the "other costs" globally correct.

One of the most simple ways to get there is to do a pilot project and have a dedicated project account so you get a analysis "money pumped into the project" versus "tons of construcction" comming out of the project.

I know that steel building in the United States is rated in 1000 - 5000 USD per ton of construcction.

So if you get a figure of 7.999 USD for your steel hull this can only be correct if the hull has a total weight somewhere between one and seven tons - if that is not so there are probably some major flaws in the calculation.

I also know from my pilot projects that i can crank out a ton of concrete construcction at USD 166 - so a factor 10 below steel standard project cost - but that is for south america.

Wil--concrete here is 190.00 per cubic meter--or about 2.5 tons per 190.00!! one cubic meter is 5250 lbs!! yes the total cost of the build is the detail things -but ive factored all that..it has to start with the hull so this is the first place to get best potential for price...

Wil--what would stop me from doing a sort of method that is used for the tunnel sections you posted previously? the idea is this-- lay a ring mold on the ground. insert rebar. the ring mold would be 6 inches in width 4 ft high and 6 ft diameter. then you mix your own concrete, make the pour. when the concrete is hardened you make 4 more of the same --giving you a pressure vessel 7 ft outside dia. and 6 inside. you essentially "weld" these together using epoxy. pipes are inserted into the mold vertically so they can fit nicely together...then an adhesive epoxy is used. this would bond the sections together...tabs would protrude through the mold to allow a steel overlay for wleding up the exoshell in light gauge steel...

what r your thoughts on this?

of course you could carry this one step further wiht a continous pour but for me this is not feasible...

1. easier to build form

2. complicated formwork are avoided

3.good for limited space

4. quality can be controlled as concrete is easily accessed

5. allows cheap forms

6. not dealing with the weight fo heavy pipe

Why do you think that a complicated way to "make it easy to work with fittings" is a necessary design feature? If you look around in concrete civil engineering all kind of fittings are used without any hardship, and your local hardware store has dozends of suitable fittings and appendages on the shelf.

I would say that creating a suitable formwork and form things in place is much easier than doing the process you describe...but i may not have a adequate perception of the grade of complexity of your suggested method.

You would have to build something in both methods and then compare cost and workhours per ton structure built ...

My current numbers are 331 Euro per ton of structure built and i would say that you can form and work literally ANY shape at that cost (at least here in south america) ...

Reading List:

Basic Concrete Engineering for Builders with CDROM / Design of Concrete Structures / Strength Design for Reinforced - Concrete Hydraulic Structures Engineering Manual on CD / Design of Offshore Concrete Structures / Construction of Marine and Offshore Structures, Second Edition (Civil Engineering - Advisors) / The Dock Manual: Designing/Building/Maintaining / Theory and Design of Concrete Shells / Thin Shell Concrete Structures / design procedures of reinforced concrete shell structures (JGJT 22-98) / Understanding Structures / Concrete Planet: The Strange and Fascinating Story of the World's Most Common Man-made Material / Concrete Construction Manual (Construction Manuals (englisch)) / Large Wind Turbines: Design and Economics / Dynamics of Offshore Structures / Offshore Technology in Civil Engineering / Design of Offshore Concrete Structures / Concrete in the Marine Environment (Modern Concrete Technology)

-- Edited by admin on Thursday 15th of March 2012 09:55:31 PM