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Nkossa Barge

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This topic contains 48 replies, has 10 voices, and was last updated by Profile photo of ellmer - http://yook3.com ellmer – http://yook3.com 3 years, 9 months ago.

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    Authors C. Valenchon, J.H. Rossig, S. Anrhs, Bouygues Offshore, France

    Offshore Technology Conference, 5 May-8 May 1997, Houston, Texas

    Copyright 1997. Offshore Technology Conference
    Language English
    Preview Abstract

    The NKOSSA Oil Production Barge, now in production offshore Congo in the South Atlantic, is the first Concrete Monohull Production Vessel, and by far the largest concrete barge ever built.
    From the unique experience of designing and building this large concrete monohull, extrapolations towards other concepts using larger vessels have been developed.
    The first step of the evolution is to add to the production functions the functions of crude oil storage, and offloading while either keeping a spread mooring for mild environments or choosing a turret mooring for harsher environments (FPSO).
    The latest and most innovative evolution is a concept for the development of deep water fields in mild environmental areas such as the Gulf of Guinea. This concept is an FPSO which performs, in addition to its usual functions, all drilling and work-over operations, while allowing dry well heads to be placed above the deck of the unit, called a “Multifunction Barge” (MFB).


    Concrete fixed offshore platforms are found all over the world including Norway, UK, USA, Australia, the Netherlands and Germany. Some of these platforms were installed over 25 years ago. They have demonstrated their excellent long term behaviour in the offshore environment, with very limited maintenance.
    After installation in the North Sea in 1995 of the Heidrun Concrete TLP (Ref. l), and the Troll Olje Concrete Semi-Submersible (Ref. 2), the NKossa Barge is the third concrete floater to be installed offshore during this decade.
    This “barge type” structure has been built within an EPC contract following an international call for tender for a steel hull, in which the bidders were allowed to propose a concrete alternative.
    The paper presents first the main features of the NKossa oil production barge, and a brief history of other concrete floaters, then the evolution of the NKossa concept to concrete FPSO’s and the Multifunction Barge is discussed.

    The NKossa concrete barge

    The NKossa Field, in production since June 7, 1996, is located 60 km off the Congo coast in water depths ranging from 150 m on the East side to 300 m on the West side. The field has been developed using two steel drilling/wellhead platforms, a production facility, and two Floating Storage/Offloading vessels for oil and LPG. It was decided to use a Floating Production Unit for the hydrocarbon processing facility and for reasons stated below, to construct it out of concrete rather than steel.
    This unit, which is the largest concrete monohull ever built, has an operating displacement of 110,000 tomes and is designed to carry a deck load of 33,000 tomes.
    The barge houses 80 people, serves as control centre for the other field installations and provides oil treatment, LPG production, gas reinjection, and water injection functions, as well as all utilities (see fig. 1 and table 1).

    Obviously floating offshore structures are divided in BEFORE Nkossa and AFTER Nkossa – my question is why is the engineering blog still stuck in the pre-nkossa era and has still not gone to concrete flat barge float concepts ?

    Is there a (good) reason why we insist in the OLDER and much more expensive elevated platform concepts ? or did we just not yet adsorb the newest developments …

    Profile photo of

    It’s about technique. Nkossa is anchored against buoyancy (anchored then tightened down) to provide solidity. Most of the seasteading ideas are for something much more mobile. Further, most ideas aren’t designed around that sort of cash-flow… It takes a lot, to build one Nkossa-type structure.

    Bear in mind that Nkossa is in relatively sheltered waters, not the open oceans… Different places have different possibilities… NOT that I can’t find something to do, with several acres. It’s already been discussed, elsewhere on here, so searching for it should be easy enough… Cost is the biggest obstacle.



    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.


    60 km off coast of congo is not really sheltered water, and it is a free floating barge on a mooring, not a “tendon concept” as Troll or Heidrun.

    Nkossa free floating on a mooring

    Deepwater tendon concepts achieving stability by tension cables to the ocean floor…

    Maybe we can start in calm water with smaller budgets and go outside EEZ when we have bigger budgets – in any case, floating structures of any of the elevated platform concepts suggested, are BY FAR more expensive than a Nkossa like chambered concrete flat float.

    In fact i have tested the smallest possible scale of chambered concrete floats and it is about 1m diameter. Rafting up 1m modules is a start you can have with very small budgets – when your island reaches 50m diameter, floating 60 km off coast should not be a problem as Nkossa does it already.

    Remember Kon- Tiki – it was a flat float of only 4m width and made it over the pacific. The seaworthyness of flat float concepts is widly underestimated ….

    Nkossa is now a decade in use and perfoming excellent – no maintenance –



    European Submarine Structures AB


    another offshore concrete raft intallation a LNG plant packed on a concrete flat raft and delivered on the ocean…

    Link to the project:

    So the paradigma that only elevated platforms can be used in open ocean conditions seems to be obsolete since 1997 – at least.

    I would suggest to update the general engineering concerns in this point.



    russia is building nuclear power plants mounted on flat raft (barge) structures for arctic conditions and selling (and delivering) those plants over the high seas to indonesia.


    SABmiller is seriously considereing floating breweries… floating data centers has been proposed…etc…

    I think we can consider the basic engineering for putting industrial installations on the ocean as a “solved problem” – the emerging concept is a big concrete flat raft structure – a simple box like structure (chambered) which has a general maintenance free life expectance of 200 years – this is sufficient for most industrial installations (they will be obsolete and dismanteled within a shorter period anyhow).

    Maybe the age of global mobility for factories has come with the nkossa barge – seasteading is happening – but a little different than TSI imagine. Not the pioneers and the political motivated go first – industry does driven by globalization of the markets and need for optimizing resources.



    European Submarine Structures AB

    Profile photo of Farmer

    Mr. Ellmer,
    I don’t know the extent of your qualifications but I’m pretty sure the rest of us are mostly dilatants and hobbyists.
    You, it appears, are either an actual marine architect or at least a concrete expert and the closest thing we have.
    You have convinced a botanist/facilities manager (me) but I can still think of two (related) arguments for the spar structure.
    1) Showbiz: The spar structure has a weird, cool, futuristic look to it. Investors and the general public like that. Very sexy.
    2) Other people’s ignorance. I’m not a dumb guy but because it is way outside my field it took me some time to come to understand it. Again, think about investors and the general public; they mostly won’t catch on for a while.
    To quote some ancient Greek playwright: “Against stupidity the gods themselves contend in vain.”
    “Give ‘em what they want.” –P. T. Barnum
    Off topic: this is why I support the schisms and infighting in this forum. Spar structure might be right for Clubstead and protecting Thiel’s U$D but not for Wil’s effort to house the Brazilian homeless.

    The showbiz effect is important – any auto firm has “exposition models” that will never make it to mass production (and they know it) but the press loves them and the press gets what they want.

    Airbus will not have a jaccuzi on board of the A380 they will stuff it with a “never seen before number of boring seats for mass transportation” – this is where the money is – but they have a jaccuzi mock up as a “available feature” in a hangar and the press loves it.

    So it is OK to give them the pictures they want. But we should have clear (at least in the engineering and management board) that what we go for is “lowest cost per squaremeter real estate” and the reasons why we go for that is massive implementation.

    If we can not compete with land real estate seasteading stays limited to “high cost does not matter sectors” what means luxury yachts, oil/gas, tourism, – what is exactly the segment that is doing it already.

    Bring the squaremeter cost down is the central task when you want to float out normal people. If we can not create a option that is available for average joe – we do not really progress towards the goal to be society relevant.

    Floating out clubstead is like building a ice hotel – the rich will enjoy the diversion in their high price vacations – but it is little relevant for society and will never be a broad movement.

    I am not sure if Brazilian homeless should be the first target – but the target should probably be somewhere the MIDDLE can afford it.

    PS: as you mention it – what about having “graphic artists” to paint the picture to the press. Do we invest in graphic arts? and do we have graphic arts from a wide variety of concepts we are talking about?


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    I think we need some clarification. You say ‘realestae’ like it doesn’t include a certain amount of open space, or land… In that case, we are actually talking about a mobile structure, whether it is ever moved, or not. The businesses almost everyone talks about, need office space, not realestate. All we’re going to accomplish, is a structure. At the hotel/resort/casino, you only use indoor space and could use the roof for the pool area, aside from that, businesses want office space, not realestate. Rather than compare apples and oranges, make it apples and apples. Pick one of the floating designs and compare the capacity to the capacity of a normal structure, then work-out the costs. Concrete and steel is concrete and steel. Techniques and quantities are different in some areas, but a partition wall is a partition wall, while a structural wall is a structural wall. The difference is between hull and foundation+land…

    How much is it to build a ferrocement silo? There’s your comparison to a spar-buoy of the same volume. Ferrocement is ferrocement is ferrocement is ferrocement. If the silo has to hold however many tons of grain, that should give a good comparison for wall strength. I’m sick and tired of all the over-inflated cost analysis that everyone quotes. Steel has a price, cement has a price, manual labor has a price… For Gods’ sake, quit trying to put a hotel on top of one, without considering the amount of spar to off-set the additional weight.

    Put a home in the top of that silo(silo caps are getting common use for conversion to homes), give the family a way to work and educate the kids, reasonable access to medical care (getting to where 90 minutes is a stretch, in the US).

    What the heck did I just describe? A FLIP! No, I didn’t use 1″ sheet steel, I described a ferrocement silo, then put the thing into the water.

    Maybe this is a rant, maybe it’s just pointing out that there are quotes and then there are quotes… At any rate, a seastead is a structure, not real estate. It’s a purpose-built building, not some permanent scar on the land, that is obsolete in 10 years. Sure, some technology will change, but that happens and people still adapt log homes…



    Never be afraid to try something new…

    Remember, amateurs built the ark, professionals built the Titanic.


    The key problem of seasteading is a real estate problem “create living space at sea at a affordable cost”

    sure, you can build a silo float it out and live in it – but it would be like living in a lighthouse a (endless stairway that eats up all of the living space) – why would you want to distribute the living space long thin and vertical. For a long thin vertical structure to work well as housing unit, you need elevators and horizontal distributed floors similar to a skyscraper. It must be so big that each floor contains a complete living space and how would you get natural light to each floor?

    There are much better ways to distribute living space than a silo.

    We already know from nkossa that a width of 50m for a simple flat raft structure gives enough stability to work well in the high seas 60km offshore . The disc shape below (foot part of the rion-antirion bridge pylon) has a diameter of 70m . It is obvious that it would work well as a seastead in the high seas. It has lots of horizontal living space – fine light conditions – and the engineering is done and tested. It could even be submerged to 70m if needed. (as it is in the bridge as we speak)

    If we can have flat living space in a simple (economic to build) structure that is stable enough in the high seas – why would we go for expensive supended platforms or fliping living space or silo living space at much higher cost.?

    Flat floats on the surface need 50m diameter to be comfortable for permanent living offshore.

    If you build smaller structures like single family seasteads you could do it (part) submerged to avoid the wave movement.

    But i would not distribute the space vertical like a silo but “bulb it out” just below the surface. This works extremly well, i tested it !

    And the light conditions are far better than it would be in a silo …

    The living space is compareable to the living space of a yacht.

    PS : probably my use of the term “real estate” is not correct – as it refers sometimes to open land – lets talk about “living space” as enclosed living space like a apartment or a office.



    European Submarine Structures AB

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    It proves the viability of floating concrete structures.

    I consider concrete habitat as a given for long term, cost-effective seasteading combined with low cost floating plastic membrane structures for agriculture and plastic mesh cages for aquaculture. Steel rusts.

    The question remains as to what form. A segmented, expandable, ringed seawall with integrated habitat, commercial, and agricultural space? A modular semi-submersible array, where the submerged flotation area is underwater habitat, supporting an above water public park or individual private patios connected with public walkways, with retractable mooring facilities and walkways at the waterline? Or a big, floating barges like Nkossa which can tile together, reminiscient of the Atlantis Project.

    The beauty of concrete is it can be cast in molds floating in the water in very large shapes, reinforced with steel or alkali resistant glass fiber to eliminate the labor intensive, rust prone, steel rebar and mesh, foamed to a neutral bouyancy or desired specific gravity, and made ductile with additives to avoid cracking.


    the general idea of a barge is that the form is easier to build than a ship – so what nkossa, the adriatic project, and the russian power plant are doing is to simplyfy the shape to a simple flat raft due to its easy build and therefore lower building cost per ton of displacement. They do so because the finished barge will not move around and therefore it does not really matter how its shape streamlines.

    Your concept includes mobility as a important part of the package – so once you decide that you want to move around streamlined you might want to skip all those edges and optimize to a steamline shape like a ship if you decide your seastead should float high in the water, or you might decide to streamline to a blimp shape for a (semi)submerged hull.

    What shape is also a question of building materials the shape above is fine for easy build with plate material but quite complicated for concrete building. Concrete works best in rounded shell structures or simple plate building. If you check the video of the building of the pylon of the rion-antirion bridge (building a 70m disc shape in drydock float it out, building a tower on top and lower it 70m deep like a spar) ( video: http://www.youtube.com/watch ) you get a quite good picture how a big floating structure must be constructed and handled – i fear the overhanging in your prefered shape is not really easy to build – so when you are obligated to go to “sophisticated forming” anyhow – why not do a much more streamlined shape from the beginning.

    The decision of shape should be taken the other way round – you should decide in what material you build then find out in detail what is easy and what hard to perform and why (by doing tests with the material) – and then optimize for easy build inside the desired mobility needs.

    Making a shape out of nowhere on your computer and declare it THE solution is probably not the best way to come up with a good shape, there is a risk that you end up sitting between two chairs hard to perform in forming and little streamlined at the same time. If you find yourself with a shape that nobody else is taking into account (no engineering design, no design of mother nature) – there are probably good reasons for that – but it may also be that just nobody has thought of it yet…



    European Submarine Structures AB

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    I did presented a design long time ago. It has mobility, modularity and scalability, as a concrete “barge like” structure.


    Later on, I did improved the original “kite module” to this.

    I added the midship section (highlighted in red), for extra space/surface area and to increase the stability of the whole structure.

    Profile photo of OCEANOPOLIS

    But since you brought it up, now I will:) The kitefloat design IS much better than anything on the table now. It will outperform by far the Nkossa, Club Stead, a hexagonal, round or square, or whatever shaped module, any spar, or submarine, or any ship or barge, etc., in terms of ALL the seasteading needs. The edges are ok, since it will have low cruising speed (under 10 kn). How high in the water its just a matter of increasing the freeboard (if this is what you meant- a bit unclear there). Also, the construction will be far less labor intensive due to the “straightness” of the design-simple plate, compared to any “curved” design.

    The biggest risk is not taking a risk and whatever other people are taking into account, or not, its really irrelevant to me because I am not looking to win a popularity or a design contest. Nor I am here to sell this design to anybody. All I am saying is that this design is good enough for MY seasteading needs, with the outmost priority on mobility and modularity and I am sharing it with the community. If somebody else has a better design/solution, even made out of nowhere on their computer, they should post it, or pattent it (if they think it’s so “valuable”) and then post it, so we all can take a look.


    ocean, once you have considered all this stuff and you are still convinced that you are on the right track – there is no way around – you MUST build it. Maybe in smaller size to keep the risk low – but at the end discussing things is not enough – you must do it.

    We will not decide the standard design of seasteading on a discussion forum. Nor a engineering team will bring it up in a contest. The best design will surge automaticly because more and more seasteaders will adopt it – build it – buy it – for good reasons they want most BANG for the BUG.

    Possibly that depends of the seasteader segment and view angle – so i doubt that the final concept will be a concept that needs a strikt tiling to form part of the seasteading community – i would bet for concepts that can integrate big and small rafts of any shape and size, normal boats, yachts, houseboats etc to participate in a seasteading community so i would bet on a “floating marina concept” instead of a “closed tiling concept” – but i may be mistaken – who knows? the future will show…

    In any case everybody who is convinced of his concept should build it and present it to the market. Those nkossa barge guys already did, so did the russians with their floating power plants, and the rion-antirion guys – those are the already presented concepts for the high road…

    Some lowroaders have also presented – we have seen hexagons, cubes, bottles, veggi floats, balsa logs, barrils …

    I would like to have some kite floats in the seasteading market race – so go for it !


    Profile photo of OCEANOPOLIS

    Of course, @ a smaller scale, as you well said. I also do agree w/you that “Possibly that depends of the seasteader segment and view angle – so i doubt that the final concept will be a concept that needs a strikt tiling to form part of the seasteading community” when it comes to my design.

    But, as a sailor, I do consider myself as part of the mariners family. The fact that mobility is paramount to me is because I have seen to many of my bretheren perish on stationary instalations, mostly oil rigs.. http://www.oilrigdisasters.co.uk/ All those fatalities happend in most of the cases when those rigs sank after being hit by a major hurricane. And no vessel could physically go thru that storm to save them, nor any captain in the right mind would risk his vessel and crew to come to their rescue. And on top of the loss of life we are talking about huge $ loss. If only this rigs could have just pack and go a week in advance,…

    If we relate this to seasteading, I can almost guarantee to anybody that 2 subjects will be the most important topic on the table when the time will come to talk investments: the safety of the people and the safety of that financial investment. The answer to this two topics will solely dictate the choice of design. To consider a design, based by any other rational other then this two would be illogical and in the long run catastrophic.

    So, to me, purely stationary seasteads are a myth, unless, of course, they are solidly embedded on the sea bottom, as a whole structure. But what are the chances for that to happen 200 nm offshore (engineering wise) and still keep on the “good side” of UNCLOS and the Internatianal Seabed Authority? Very slim,…

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