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Modular-built tethered floating island

Home Forums Archive Structure Designs Modular-built tethered floating island

This topic contains 15 replies, has 8 voices, and was last updated by Profile photo of xns xns 4 years, 11 months ago.

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    Profile photo of darcyj

    I’m new of course – you can see that from the list of newbies on the left. Had an idea some time ago and this seems like the best place to share it.

    (Feel free to direct me to an existing thread if this has been proposed before).

    Firstly, location is important. In order to claim independence from the control of existing nations, a “new” island needs to be more than 200 miles from any coast. Various aspects of maritime law, including Exclusive Economic Zones, serve to put an end to any inshore proposals. This has implications for service and supply of any people living out there, but that is for another debate.

    Given that the structure is to be more than 200 miles from any coastline, it runs into problems of construction and tethering. The latter is not a huge problem, provided you have the means to install anchoring fixtures on the sea bed at a depth of as much as 2000 metres. Having the materials to make the actual tethers is a non-issue; if you are engaged in a construction project like this, then you can make a 2km chain (or to be more precise, twenty of them).

    Construction is therefore the first issue, and it comes down to design. If the entire structure is built on land or inshore, then towing it out to the final location is a massive project in itself. Alternately, building modular pieces allows each one – smaller and lighter in weight – to be taken out to site individually. In fact, a modular design allows the structure to be extended almost indefinitely. Certainly, if one is to build an island large enough to hold a runway, then one-piece construction is never going to be practical.

    How should the modular pieces be designed? Buoyancy is the key, because even though the whole structure will be tethered to the sea floor it will still be floating. Design must take into account the weight that will be carried on the structure, and in my mind a flat featureless platform is no place to live. I want to import a landscape, which will mean thousands of tonnes of soil and rock. Each modular piece is going to share a percentage of this huge weight, so in order to maintain buoyancy the weight-to-volume ratio of the piece itself must be very small.

    I suggest a carbon-fibre material, which is very strong for its weight and which is very resistant to material degradation. The worst thing for carbon-fibre is sunlight – and then only over a period of decades – and if our carbon-fibre construction pieces are mostly submerged and covered on top with landscaping materials or building structures then they will not be exposed to light at all. A carbon-fibre cylinder, closed at both ends, will float and will continue to float even bearing a large weight; make the profile hexagonal and they can be linked together along their vertical length with the hexagonal top ends tesselating to provide a continuous platform.

    Due to the lack of weight being borne by the structure early in its life, a system will be necessary for partly filling the modular pieces with water for ballast and stability. Once there are enough of them joined up that the platform is larger than the height, it will never capsize but the platform will be way above the waves. So the top end of each modular piece should be equipped with access hatches to pump ballast water in, and pump it out again as the surface infrastructure in put in place.

    The first group of modules which are linked up at sea would be all tethered to the sea bed anchoring points; when the last modules are installed on the perimeter, these would also be tethered. The tethering system would ensure that the island stays at its precise longitude and latitude and does not change its orientation. It would be as stationary as a true island.

    Reading another thread, it also occurs to me to mention failure mode, and a modular construction is almost completely failure-proof. Install sensors inside each module to reveal if and when the bottom has been breached, and a repair crew can deal with it, but meanwhile the effects on the stability and integrity of the whole would be insignificant. Only if a majority of the modules were holed underneath, severely impacting the total buoyancy, would there be a problem but such an event would likely be due to sabotage and so your problems at that time would be many.

    Design possibilities for the shape of the island are almost limitless. The island should enclose a harbour, and should be large enough that imported rocks and soil can be used to build a cross-island ridge upwind of the main “town”. It would also be good for an outer perimeter of modules to be deliberately placed below sea level, so that the shoreline of the island behaves like a true shoreline, with waves rolling in over the shallows. You could even build beaches, headlands and other coastal features as the years go by, provided you remember that every addition of weight affects the total floatation. For this reason, a whole-island landscaping design is best done before design of the floatation modules, so that their very size will be known before fabrication begins.


    Profile photo of thebastidge

    “Certainly, if one is to build an island large enough to hold a runway, then one-piece construction is never going to be practical.”

    Aircraft carriers are not modular. A passenger aircraft along the lines of a 747 is probably never going to land on such a structure, modular or not. Light aircraft, seaplanes), zeppelins, and VTOL/rotary wing aircraft are more likely than jets.

    I agree about creating a landscape- it’s important if the place is ever to be attractive to anyone who hasn’t been floating in a liferaft for 3 weeks. I don’t think that the landscape has to support all one’s needs for space and life support. I think that cubic underneath is important for living space, and housing the machinery necessary to living more than a subsistence lifestyle. The landscaping up top is sustenance for the mind and spirit.

    Having a basic plan for the structure has benefits, but flexibility and modularity can correct for unforeseen issues. Better would be to have principles for construction and growth that new additions can be evaluated with.

    Profile photo of darcyj

    “Aircraft carriers are not modular. A passenger aircraft along the lines of a 747 is probably never going to land on such a structure, modular or not. Light aircraft, seaplanes), zeppelins, and VTOL/rotary wing aircraft are more likely than jets.”

    You may have noticed that aircraft carriers launch their lightweight jet fighters from a catapult, and use arrestor cables to stop them when they land. A somewhat longer runway is needed for any kind of aircraft that is to carry civilian passengers and cargo. To accomodate light passenger aircraft like the DASH-8, CRJ or Fokker 50, a runway of 1900 metres is preferred. And don’t think that tourism would be the least significant money-earner for an artificial island in temperate waters … so you need to be able to offer tourists a comfortable way in and out.

    I do concede that in the early years you are only going to see helicopters and other small aircraft, but that doesn’t mean you ignore the future possibilities when designing the island.

    So, with that in mind, I am designing the island to be around 4 milllion square metres* in surface area above the water, or about 4.5 million square metres of module surface including the submerged coastal fringe. If each module is 25 metres in diameter then that means around 7500 modules – it would have been more but there is no need for a complete coastal fringe, especially in the harbour. Make it 100 meters long, and you have a bit over 19500 square meters of carbon fibre material for each one; plus connection nodes, plus access portals for pumping ballast as described earlier. Each module could support nearly 40000 tonnes floating, so the entire island complete with landscape, buidlings, equipment, inventory and people should not exceed about 250 million tonnes – equivalent to the weight of a 20-metre thick layer of concrete covering the whole island. It is obvious, however, that you would not have 20 metres of concrete in most places, so that gives us the capacity to build a line of hills up the middle maybe 150 metres in height. Piling the majority of weight there also aids with overall stability; the landing of a 20 tonne aircraft on one side would not upset the equililbrium.

    Add to that the cost of towing each one out to the site and the logistical problems of actually joining them, and of course the unquanitifed cost of setting up the sea floor anchoring system. I mentioned a 2km sea depth in my earlier post, but my target site for tethering is actually not that deep – Gascoyne Seamount, a mere 653 metres under the Tasman Sea between Australia and New Zealand and not within the maritime jurisdiction of either.

    Estimated construction time in excess of 20 years and that’s assuming a continuous production of these large modules. I didn’t say it would be cheap, but it is well within technological feasibility and would be quite impressive if ever built.

    John P Darcy

    Profile photo of vincecate

    >So, with that in mind, I am designing the island to be around 4 milllion square metres* …

    Doubtful you can build this for less than $1,000/sq-meter. So you are talking over $4 billion. Any new country plan that has as step 1, “raise $4 billion”, seems bound to fail.

    The hard question is what can you design that is really affordable for a single family or small group of non-billionaires yet comfortable and safe in the open ocean.

    Profile photo of darcyj

    Regarding $4 billion, that’s not very much money from a certain perspective, and if it is $4 billion of today’s money over 20 years – $200 million per year – then we are talking somewhat less than the annual profit of a moderately-profitable Fortune 500 company. Get ten Fortune 500s to sponsor it and formal development would begin tomorrow. (Problem with that is selling your soul to big business, but that’s where you have to be creative in what your side of the contract is offering).

    For a single family or a small group of non-billionaires, to be comfortable and safe in the open ocean, the word you are looking for is “ship”. They’ve already designed and invented those. My design, although not exactly what Seastead is aiming for, would result in a genuine piece of new land large enough for diversity of usage, population growth, and accrual of external revenue through tourism and port services for deep-sea fishing.

    Profile photo of vincecate

    Ships are designed to move through the water from point A to point B. If you are not trying to get somewhere they are probably not the optimal design. There has not been much market for living space on the ocean so not a lot of effort has really gone into designing for it.

    I think my own design can give a family something much more stable for a given amount of money than a ship.


    If you think you can raise $4 billion, go for it. But don’t be offended if nobody here, or wherever you go, takes your plan seriously. Many projects before also had plans with step #1 of, “raise X billion dollars” and ended up stuck on step #1. Can you name one startup company that raised X billion dollars before they were delivering a real product or service? Such a plan reflects poorly on the planner in an investors eyes. Don’t you think there is some plan that can get started on a smaller budget and grow into a big thing? Wouldn’t that be a better plan for investors? Wouldn’t that plan have a better chance of getting enough money?

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    • Modularity is probably a good approach for getting costs down. But the structure must be suitable for modular construction. For instance the joints between modules must be strong, easily assembled, and not excesssively bulky or heavy. Personally I´m having a hard time decoding what kind of structure you are proposing. A picture would probably do wonders here.
    • Nobody is going to invest billions of dollars in a scheme that hasn´t yet proven some sort of actual success. Start small and prove the concept first. If it works the money will come looking for you.
    • Ships are fine, but they are made for transport, and must avoid severe weather. For me one of the points of seasteading is designing something that doesn´t need to do this, so it´s occupants won´t have to interrupt their lives and/or business operations too much every time there is a storm. I agree that while ships doesn´t advance the core seasteading technology, the structure, other areas might still benefit, so it wouldn´t be completely useless.
    Profile photo of darcyj

    “Personally I´m having a hard time decoding what kind of structure you are proposing. A picture would probably do wonders here.”

    Well, I wish I could draw :(

    The top side of each module is hexagonal, slightly convex for structural rigidity and with ribbing underneath to further reinforce the load-bearing ability. At one edge is a large hatch for access underneath.

    Each module is a hexagonal prism. I used the figures 25 metres and 100 metres in my original post, so that each module encloses 40600 cubic metres of volume – in effect, a float to carry up to 40 tonnes. Individually, such an object would float horizontally, but when joined along their length a group of them would float in the intended orientation, ie, the hexagonal faces top and bottom.

    The inside walls of each module have ladders and ledges for working access, and a hose system to allow pumping of water in or out (for ballast purposes, or in case of unintended holing).

    Joining methods are many, but some can be dismissed – for example, bolts driven through holes would inevitably lead to leaks. The linkage mechanisms need to be on the outside of the module, and need to be numerous because of the potential maximum load carried on any one module.

    So, after ballasting a module it would be manouvred by tugs alongside the existing structure, and pulled/pushed into place. In due course, you would have a surface area large enough to install infrastructure. The ballast in the modules holds the structure down close to sea-level, but as more weight is added on top the ballast needs to be pumped back out to maintain equilibrium.

    Finally, several of the first modules taken out to site, and a whole bunch of those at the centre of balance of the final structure, have anchoring rings on the bottom side from which are strung long chains for anchoring to the sea bed.

    John P Darcy

    Profile photo of Jesrad

    I really like the idea of modular building for its versatility and its easier scaling. Since we’re talking about coupling techniques, I’d like to point out that there are modern materials that join nearly-miraculous flexibility with high rigidity.

    For a quick example picture, if you will, very long composite beams passing through holes in the top of barges’ walls for tieing together three such barges in a line. Toss in a few used truck tires on the sides to protect the walls from colliding. Cross the beams, and you can join any number of barges by filing the beams through one way or the other. As long as this coupling resists having one barge almost entirely out of the water and the other being entirely submerged, it should resist rogue waves (basically, if you can suspend the entire weight or an equivalent amount of buoyancy of one full barge onto the beams of the others).

    Building large enough individual pieces so they survive the ocean’s direst perils might not be feasible, especially at the start. Building low enough or light enough or flexible enough could, though.

    I’d advise against hexagonal, and in favor of triangular or square shapes instead for prism modules, but that’s just personal preference.

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    So this is like a giant floating hexagonal M&M? How about storms and rogue waves? It sounds like something like this would be tossed around quite a bit in rough water, as well as completely washed over with water quite frequently. This would make the top deck unavailable for anything but temporary or expendable things, and everything inside would need to be nailed down. Unless I´m missing something.

    Profile photo of darcyj

    Stability is ensured in three ways:

    1. Depth in the water. The modules are 100 metres from top to bottom, so when the top side is encumbered with infrastructure and landscaping, and ballast is added to achieve the desired floatation level, the whole thing is 95% submerged. Like a boat, the heavier and deeper the keel the more resistant to being tossed around it will be.

    2. Sheer mass. It would take the storm of storms to trouble something weighing 250 million tonnes.

    3. Tethering. The thing will be tied to the sea floor by a number of cables, primarily to ensure that it does not move and that it maintains orientation; but these cables will also prevent tilting.

    The large size and mass also stops the whole thing behaving like a see-saw when a person steps on one side and a helicopter takes off from the other side.

    As for being washed-over by waves, you are assuming that the platform is going to be one metere above wave level across its entire surface. This is not what I envisage. A preferred design is for the modules to be connected in such a way that those in the middle of the island are higher than those at the coast. Further, the landscaping part of the project is intended to give the island the gross characteristics of a real island. Waves will crash against the shore and run up the beach or bounce off the rocks.

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    • Ok, we´re talking megaprojects here :-). I agree something that big probably could endure most things nature could throw at it. Basing the seaworthiness mostly on sheer size and mass it doesn´t really lend itself to incremental design though so I guess it´s an option for when seasteading matures and starts attracting the really big bucks.
    • What dimensions are you talking about? A hexagon 100m high and what, 500m across?
    • You mentioned carbon fiber but I´d have to say that something like this would work just fine with reinforced concrete. When you depend on a high mass for stability there is no point in spending a fortune on expensive light-weight materials.
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    Modular construction is pretty much the only game in town.

    Carbon Fiber is a great material, but it is quite expensive. Most current maritime construction uses steel, aluminum, fiberglass, and concrete. The aluminum and fiberglass is used in the lighter structures and the steel and concrete is used for the heaver structures.

    The maritime law around EEZ’s is evolving. Many countries are using the EEZ concept to basically land grab continental shelf and incorporate it to their country borders. There is plenty of room to disagree with me on this opinion, but I ultimately think countries will successfully land grab all of the continental shelf area.

    Deep sea mooring is pretty challenging and expensive. Once you get off the continental shelves, there is no real reason to moor anything. Just free float.

    The Seasteading Institute is focused on smaller and more economical platforms. Raising billions of dollars for a project that does not have much of return on investment is pretty hard.

    Profile photo of thebastidge

    Not to mention, what happens to the sea under such a massively wide construction? How is photosynthesis accomplished for algae? What happens to the marine life? How does it affect the localized weather and sea conditions?

    Profile photo of GulfRealm

    http://pelagic.wavyhill.xsmail.com/index.html has pictures and design possibilities for hexagonal ferrocement floating platforms 50′ (fifty feet) in diameter, 10′ (10 feet) thick. Their calculations indicate that said platform would support 380 tons. Their concept is to live inside the platform. I think it could be built similarly but used to support a habitat while completely filled with foam to make a sink proof platform. Similar to Richart Sowa’s Floating Island (sans 2 litre bottles). The unloaded platform floats about 7′ out of the water. Multiple platforms would increase size (30 would give 1 acre of surface). Wave accentuators could be attached and do double duty as small boat moorage.

    Brother Glenn

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