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When evaluating these designs, there are several issues which come up frequently.
Our main concern with fixed-locations is political insecurity. If some country claims that you don’t have the right to be there, the colony is screwed, as relocating is likely to be very expensive. Colonists may not be willing to move there in the first place because of this risk. A free-floating design can always just move on. When you’re talking about an expensive capital outlay (analagous to a house plus part ownership of the local utility company), the residenst are going to find that level of security invaluable.
One could point out that the same pair of options is true today in normal countries, yet we usually choose to live in buildings rather than RVs because the political inflexibility is worth the extra room. But at sea, the tradeoffs are quite different, because the cost of moving buildings is so low. It is possible to have a house-like amount of space with car-like flexibility. Additionally, the potential dangers are more serious because of the uncertain political position of seasteads. Hence the fixed strategy is much less attractive.
Admittedly, there are advantages to a fixed location. One can discover and exploit local resources. Building costs will be cheaper. The colony can establish trade routes, and lay fiber optic lines. More long-term planning based on weather and local resources becomes possible. Pollution and bad waste practices are less likely. For these reasons, some groups may choose this route. However, we see political freedom as the fundamental motivation for seasteading, and freedom of movement is an important part of getting and keeping political freedom.
Add Vince’s Migration stuff http://seasteading.org/stay-in-touch/blog/3/2008/06/23/migration
Besides the underwater solution, which we find unattractive, there are three basic ways to deal with waves. We can avoid them geographically (doldrums), stop them with breakwaters or rise above them with pillars. We’ll focus here on comparing the latter two methods.
The crucial difference lies in how the two methods scale. A breakwater for ocean waves must be massive, it can’t be built on a small scale. On the other hand, if you think of the breakwater as forming the perimeter of a circle with the colony inside, you can see that as the circle grows, the size of the breakwater grows with r, while the enclosed area grows with r^2. This means that the ratio (how much breakwater is needed per unit area) falls with 1/r, which is a huge economy of scale. In other words, a city 10 times larger will be 100 times cheaper per block. So for large colonies, breakwaters will be cheap, for tiny colonies they’ll be tremendously expensive.
Pillars, on the other hand, have no such economy of scale. If you want to build another unit of area, you need the same amount of pillar as before. However, each individual pillar is fairly small, a small platform only needs one, and their cost is not out of reach of a new project. Thus pillars are well suited to our incremental approach. Still, one of the great things about the ocean is that there is plenty of room. So the high marginal cost of pillars is somewhat unfortunate, in that it makes using this space expensive.
This suggests to us that for small, initial seasteads, the pillar is a much better method. As the communities grow and become city-sized, they will reach a point where breakwaters become cost-effective. So while breakwaters are not suited to the initial stage which we’re focusing on, they will be a crucial way to bring down costs later, and let us expand into all that cheap, unused real estate.
There are several other factors to note. Breakwaters can be used to obtain energy while damping waves. It is easiest to build them in fixed locations, which is problematic as described above. However it is possible to build a floating breakwater with a rigid connection to the colony, so the problem is avoidable.
Another worry is that by fencing off a fixed area, breakwaters may lead to a static geography. That is, if a single government has control of the area, they are a monopoly. Because of the economies of scale, residents can’t just leave and start their own colony cheaply. This is not insoluble, but it is something to be aware of.
The level of modularity in our designs varies greatly. Sailboat fleets, for example, are quite modular. Individual boats can leave or shuffle around as they wish. A big boat, on the other hand, is monolithic. Modularity is important for two reasons.
The first is dynamic geography. In order for DG to function, small groups of residents must be able to move their personal space. We think this is crucially important to making this new way of life better than the old. Hence we are skeptical of fixed-geography designs.
The second reason is to allow for incrementalism. A modular structure is likely to be amenable to an incremental approach where one module at a time is built. We think this approach is vital to actually making a floating city happen. Thus designs which require a large initial capital outlay do not seem promising.
Just like a car buyer, seasteaders must ponder this age-old conundrum: lay out the dough for something new, customized, with a long life ahead of it, or thriftily convert someone else’s throwaway. While we tend towards the new approach, the issue is certainly not clear cut. A new, strange-looking seastead will feel to the world like a different way of life. This helps our political ends, as well as marketing appeal to prospective residents. It can be designed specifically for a permanent, comfortable, settled ocean life - which is not true of any existing structure. On the other hand, there are many large boats and oil platforms which are no longer useful for their original purpose, and can be bought quite cheaply considering the materials which have gone into them. Avoiding design work may lead to an imperfect solution, but at least it gets there sooner.
What tilts the balance for us is the surprisingly low cost of the structural portion of a seastead. (Renewable energy technologies are more expensive, but they would be needed in any design). Because designing and building a seastead is not that expensive, we see less reason to go the cheap route.
When talking about how we’d like to revolutionize the governing industry, we used the metaphor that we’d like government to be more like the internet industry than operating systems. One of the properties of the internet is that it is based on a variety of open standards which allow many diverse programs, companies, machines, and people to interoperate. We’d like seasteads to have this property also.
For example, the internet has a “protocol suite”. As Wikipedia decribes:
A protocol stack (sometimes communications stack) is a particular software implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them.
Individual protocols within a suite are often designed with a single purpose in mind. This modularization makes design and evaluation easier. Because each protocol module usually communicates with two others, they are commonly imagined as layers in a stack of protocols. The lowest protocol always deals with “low-level”, physical interaction of the hardware. Every higher layer adds more features. User applications usually deal only with the topmost layers (See also OSI model).
The same ideas apply to seasteads - we want to set up standards that various levels of groups of seasteads can follow, and allow individual structures and designers to innovate within that standards. For example, there will be a hardware definition for seastead attachment, specifying how to do structural attachment, how to do infrastructure attachment (network connections, perhaps power/water). We also need social protocols - What rules govern each seastead? What are the default rules? How different can the rules be? How do you know when the ruleset has changed?
Later, in the Infrastructure-Government section, we suggest that all seasteads should have a liberal exit policy, so that we know all societies are freely chosen by their inhabitants. This can be viewed as a very high-level part of the protocol suite - and will require further definition to manage reputation, handle debts and outstanding criminal offenses, and so forth.
A good set of standards will allow both modularity and innovation, and will require a great deal of thought and refinement.
There is an obvious tradeoff in structure size: small structures are more modular, allowing location decisions and upgrades to be made at a small granularity. Larger structures have more economies of scale in manufacturing and operations, and thus will be cheaper per resident. The choice of spar vs. flat seastead will have a strong impact - the spar is a large overhead cost which will be cheaper if shared, whereas the small concrete boxes to support flat structures are likely to be very cheap at any size.
Until we know the cost curve, we can’t determine a structure size, however there is one non-obvious consideration we’d like to mention. Seasteads are not merely structures to be engineered, they are homes to a community of people. And surprisingly, science has something to say about how big a community should be. Robin Dunbar hypothesized that part of the advantage of a big brain is that it allows you to have a larger social group. And he found evidence - within a species (such as primates, birds, reptiles, or fish) there is a very strong correlation between the logarithm of brain size and the logarithm of group size.
Based on human brain size, our optimal group should be about 150 people. And indeed, 100-150 is the size of hunter-gatherer tribes, military units, and the number of names in the average Rolodex of a modern city dweller. This is the largest group that is still small enough to keep track of reputation, favors granted and owed, and to all know each other. Groups at the high end of this scale require significant time devoted to social interaction, so 50-100 may be a more reasonable range. Some more recent evidence from social scientists who examine guilds in online role-playing games (MMORPGs) has confirmed this, see [[Allen200508][refs.html#Allen200508]].
So while individual spar-seasteads may not be economically feasible, we should be careful not to let structures get too large. Our vision is of seastead cities as dynamically-shifting entities composed of modular parts, so it’s important for those parts to be small enough to hold a well-connected community, which can make good decisions about where it wants to fit in. If seasteads need to be larger than 150 people, we should consider subdividing them into 50-150 person sections.
Our preferred material is ferrocement, which is cement reinforced with iron rebar. However, a large number of previous ventures have proposed using an interesting material called seacrete. Our skepticism of this substance bears explaining.
For boats: material summary here.
{ Should we also explain other engr. mat. considerations in the marine environment? ie stainless, coatings, sacrificial anodes, plastics… }
Professor Wolf Hilbertz came up with the fascinating idea to create a material by submerging an electrified wire mesh in seawater. Minerals are drawn out of the water by the current, and a cement-like substance is slowly grown by accretion. Eric Lee [Lee] has done a very complete analysis of the use of seacrete as a marine construction material.
The number of 4.2 lbs / kWhr (1.9 kg/kWhr) cited for seacrete energy requirements in places like [Savage1992], if correct, would make it quite efficient. Unfortunately, this figure has two serious flaws. First, it is based on a single experiment [Hilbertz1979]. Second, it is off by a factor of 42 due to a computation error, as Eric Lee has demonstrated. Rather than integrating power over time to get energy, the power used was taken as the energy. The process took 42 hours, hence the error. In fact, at maximum theoretical efficiency the rate is only 1 kg/kWh, and practical efficiences are much less than this. Hilbertz’s published experiment produced only 0.046 kg/kWhr. At this rate, the energy alone costs well over an order of magnitude more than just buying cement.
There are additional problems. The major power loss is resistive heating of the forming seacrete. This is because the electricity has to get from the mesh through the seacrete to the seawater, and the seacrete is not a very good conductor. So of course the thicker the seacrete gets, the worse these losses will be. If you want to make structural walls for a sea colony, this is a definite problem. You can reduce resistance using a 3d wire mesh, but such meshes drastically increase the cost.
Because you are trying to replace such a cheap material (ferrocement), it doesn’t take much to make seament uneconomical. In fact, there are some ways in which the ocean is the worst place to use seament. it’s a place where energy is expensive and transportation is cheap. Using seacrete instead of importing cement is choosing to use energy instead of transportation - a poor tradeoff.
Marc Piolenc has suggested one interesting way of making seament worthwhile. You could set up a structure and some renewable energy scavenger in a remote place, then leave it for years to do its work. Even though the process is inefficent, you can replace efficiency with time if your source of energy is the kind which keeps on producing.
However attractive the idea of turning seawater into cement, seacrete appears to be a poor choice as a construction material. In practice, it is probably easier to use boring concrete and steel to build economical marine structures.
{ how much should we say here? }
Our building material of choice is reinforced concrete, also known as ferrocement. It is a composite of two materials: steel rebar and concrete (which is made from cement and gravel). The steel has a very high tensile strength (it’s hard to break by pulling), and the concrete has very high compressive strength (it’s hard to crush). The combination is a material which is strong under many loads. Since it’s mostly made out of rocks (which are plentiful) it’s extremely cheap.
In the image you can see the framing system used for ferrocement construction. First a rebar mesh is built, then concrete can be troweled on, or forms can be built and the cement poured in. One advantage is that once a set of forms has been built, they can be re-used many times (this is true for fiberglass as well, but not steel). Also, since this is an extremely common building material, there are a huge number of ferrocement books, supplies, consultants, and contractors.
While it is not as popular as steel and fiberglass, ferrocement has a long history of use in the marine environment. It does require some special treatment, however. Over time, structural stresses create small cracks in cement. While this is not a problem on land, in the marine environment saltwater can seep in and corrode the rebar. For this reason, all surfaces will need to be carefully sealed. In our case, this means two layers of sealant. First will be Ashford formula, which makes it very difficult for water to penetrate the concrete. However, pressure over time will cause water to slowly seep through this, so an additional coat of epoxy will be used on the outer surface. Internal surfaces will only be exposed to humidity, not pressure or direct water, so the Ashford formula alone is sufficient.
An alternate possibility is to use a treatment like Xypex, which fills the pores and capillary tracts of concrete with impermeable crystals. Also, fibers can be added to the cement mix to add extra strength against cracking. Whatever system is used, it will be important to check occasionally to ensure that corrosion has not occured. The easiest way to do this is with a commercial device which examines the electrical resistance of the rebar lattice.
[INTEGRATE THIS]: Kurt Horner writes: “I’m a structural engineer in California and sometimes I’ve done concrete construction near the ocean. The typical solution is to put a anti-corrosive additive into the concrete mix and buy epoxy-coated rebar. The coated bars are about twice the price of regular bars, but this is a lot cheaper than coating the whole structure. This is especially true since the forces that will crack your concrete will also tend to crack your outer coating as well, rendering all that work somewhat pointless. That’s not to say there isn’t value in an outer coating, but rather than just papering over a problem, I’d recommend making the structure itself corrosion resistant.
Another way to stave off corrosion is to ensure that the exterior face of the structure is the compression face. This would entail making the exterior of the shaft a series of concave arcs (like a starburst in cross-section) rather than a simple tube. This would substantially reduce cracking on the exterior face.”
For interior, non-load-bearing surfaces, the full strength of ferrocement is not required. There are several alternate concrete formulations which are not suitable for holding up buildings, but feature the same durability and convenience. There are two basic ways of making them.
The first is to bulk up ordinary cement by adding foam. This can greatly reduce the cost per unit volume when strength is not a priority. One method is to add 1-20 pounds of powdered aluminum per ton of concrete to the mix. The alumnimum foams up into gas, and can double the volume of the resulting product [TechTopics2000]. Another technique is to generate foam from soap such as dishwashing liquid. This can be done with a cheap homemade device and an air compressor, and the result also has about half the density of ordinary cement. Plans for such a device can be found at [Pelagic], and a picture of Wavyhill’s experiments is shown at right.
The second method is to substitute a weaker, lighter, cheaper material for the gravel constituent of concrete. One example is “papercrete”, which is a form of concrete using paper instead of gravel. The paper is mixed with sand, cement, and water to form a material which can withstand 300 psi and has an insulation value up to R-2. While papercrete holds its shape and is reasonably strong even when wet, it is not suitable for very wet environments (like exteriors or bathrooms) as it soaks up water quickly and dries slowly. When free paper trash is available, papercrete is even cheaper than ordinary unreinforced cement [MotherEarth2000].
While concrete is normally poured into forms, it can also be sprayed into place using a mixture known as shotcrete. This can make construction much easier. For example, it is a key part of the construction technique used to build monolithic domes like the Eye Of The Storm mentioned earlier. These structures are cleverly made by inflating a large plastic form, building a rebar lattice, and then spraying on shotcrete. This avoids the need to build house-sized forms, since the inflated plastic provides the shape. As we’ll describe later, similar techniques may help us build seasteads without a shipyard.
{ Should we describe MDI process in more detail here? What should we say? }