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{ I’m not sure of the best title for this, Transportation is pithy but its about staying still as well as moving. Its really more about “location control”, but thats kinda awkward.}
Is the seastead a boat or an island?
If it’s an island, then it should be attached to the ocean floor to prevent it from moving around. Since the ocean floor is typically miles from the ocean surface, this is actually quite challenging. Seamounts and shallower areas present less difficulty, but using them greatly reduces the number of potential locations.
Our preference is to treat the seastead as a boat. For one thing, this means that all of the international law that applies to boats can be applied to a seastead. In addition, the seastead may be able to avoid bad weather (by season at least, even if it’s not nimble enough to dodge individual storms). Also when supplies are low, the seastead can find a port and resupply itself.
Once the first few mobile seasteads have been deployed, they can aggregate by simply rendezvousing at a agreed upon location and lashing together into one bigger sea village. Over time the sea communities will evolve to sea cities. Whenever someone becomes annoyed with the current state of a seastead community, it is possible to just disconnect and take their seastead someplace else.
Mooring equipment is very expensive, especially the lines. Unfortunately the lines limit what depth water one can anchor in. For example, a set of High Molecular Density Poly Ethelyne (HMDPE) lines for anchoring in 2500m of water costs approximately six million dollars - without the attachment hardware or anchors. These and other synthetic lines are the only real acceptable solution for deep water anchorages, as braided steel lines are too heavy and can corrode. In shallower water, however, the lines become proportionally cheaper.
The anchors themselves are fairly simple suction devices, basically a hollow tube with a cap on one end and a pump in /pump out valve. You drop the anchor to the bottom, pump out all the water, and it sucks itself into the sea floor. To retrieve the anchor you pump it full of water and it pops out of the sea floor. The sea floor for the most part is covered with about 50’ of sludge and muck which actually makes for a pretty good hold.
Because of the high cost of lines, potential anchoring locations are limited to areas of relatively shallow water, such as seas and coastal areas. In the deep ocean, seasteads will just have to drift, unless they anchor on a convenient seamount. Still, an anchoring system will be quite useful and is likely to be one method for location control.
An other alternative for station-keeping is to have steerable propellers connected to a GPS (Global Positioning System). The system would push the the seastead to its desired location whenever it starts to drift off location. However, this would continually use fuel, so is most likely to be feasible when drifting forces are quite low.
Newton’s first law of motion tells us that a seastead will happily sit still unless external forces act on it. The main external force moving a seastead is the action of ocean currents. This suggests an additional strategy for keeping still, which is to go someplace where there is not much current. The equatorial doldrums are one such place. Another is the center of the circular current gyres, where millions of tons of trash has accumulated [NaturalHistory2003]. This “do-nothing” strategy has the wonderful advantage of being cheap. However it had best be accompanied by a plan to deal with the possibility of being pushed around by an unexpected storm or current.
The submerged flotation gives seasteads a lot of drag. However, friction from drag is proportional to velocity squared, so as long as we move slowly it’s still manageable. Renewable energy could be used to directly power a propeller. For example, simple vertical-axis wind turbines could be connected directly to propellers, or the up-and-down motion of waves could be converted to rotation. Or we can use our standard methods of electricity generation to power electric trolling motors. These methods will appeal to the environmentally conscious, since they do not require burning fossil fuels, and may even prove to be cost-efficient. However, they are unlikely to generate much speed.
The simplest method is probably for a separate, diesel-fueld tugboat to pull the platform. Used tugs can be had for anywhere from $50K to millions [Tassins Marine Transportation], depending on their age and the power of their motors. One advantage of a tug is that it could be used to lug barges of supplies back and forth when the seastead doesn’t need pulling. Diesel engines could also be built into the structure. A powered seastead could potentially be connected to an unpowered one and used as a tug itself.
Active propulsion will clearly work for small course adjustments, or occasional location changes. It is unclear whether it will be feasible to use continuously. Even though our speed is slow, we are moving a large object, and currents will constantly be pushing us. So relying on active propulsion will add to the operating expenses of a seastead, as well as reducing its self-sufficiency due to the huge energy drain. Under the tourist business model, however, it may be practical. Cruise ships move around constantly, at fairly high speeds, and are profitable while doing so. A more permanent population, however, has less reason to move and more reason to cut daily expenses.
The easiest method of unpowered movement is drifting. This is not so disastrous as you might think, because ocean currents are roughly circular, as can be seen in the currents section. With some fine-tuning, a seastead could be pulled by them forever, circling towards a pole and then back to the equator. Moving radially will change the cycle’s period, which may be desirable to avoid seasonal storms. Active propulsion can be used to transition between current formations. A Deep-Seastead could potentially enjoy endless summer by switching hemispheres twice a year when the current brought it close to the equator. Another option is to go someplace like the equatorial doldrums where there is little current, and drifting basically means staying still.
Sails are an interesting propulsion option. They could be deployed in the space below the platform and above the waves, with the spar itself acting as a mast. A keel would of course be necessary, perhaps by making the submerged flotation oblong in shape. Because water is much denser than air, it takes a high ratio of sail area to wetted area to propel a boat. Seasteads have a lot of wetted area, so they’d need a lot of sail. Large sails are quite expensive, movement would be slow, and a square-rigged seastead would be unable to head much into the wind. The fact that the wind is a powerful sustainable energy source may turn out to compensate for these disadvantages, or it may prove to be an impractical option.
An even more interesting and difficult idea, suggested by Corwyn, is to use a submerged wing to “sail” the ocean currents. Wings work by converting the flow of a fluid into sideways motion via Bernoulli’s principle. Sails are one example of this, using air as the fluid. Water is also a fluid, and hydrofoils use this to lift their hulls out of the water with force from submerged wings.
Because fluid must flow past the wing, one uniform current would not be enough. The seastead would drift with it, and the water would appear still. In order to sail, we need a varying current, so that we can use the differences to generate motion in other directions. Fortunately, it is not uncommon for the currents at the very surface of the ocean to be different than deeper currents. The thermocline, a region of rapid temperature change, is usually 10-200m down, and it seperates the surface “mixed layer” from deeper waters. Currents are often different above and below the thermocline.
There are substantial problems with this method, of course. Current differences are likely to be small and variable, thus imparting little speed and requiring re-adjustment of the angle of the wing. Transmitting the forces along masts long enough to reach into regions of varying current is difficult as well. It may not be feasible. However, there is a certain elegance to this method of propulsion, and it would be truly magnificent for a seastead to sail, not drift, in the ocean’s currents.
Reader Edward T. Felton suggests a variation on this, with an underwater kite instead of an underwater sail. That is, suspend a structure with large cross-section from the seastead, reaching down to the desired current region. It will then pull the structure in the direction of that current. While this allows for less flexibility in direction of movement, it also poses less engineering challenges.
Besides moving around the entire seastead, we’ll need various methods of bringing people and goods there and back again. Obviously the size of this cargo stream depends on how much the seastead is importing (its self-sufficiency), how much it is exporting to the world, and the size of its tourist industry. If the seastead is functioning as a resort, it is crucial to have good ways of getting passengers there and back again. The closer to land, of course, the cheaper this transportation will be. There are two basic methods of moving over water:
The slowest and cheapest method is floating, whether on a sailboat, rowboat, motorboat, or experimental rocket-powered hydrofoil. Boats typically have speeds of around 10-30 knots. Thus a seastead just outside the 12 or 24 n.m. territorial water limit could be reached in 0.5 - 2 hours. Getting to a seastead outside the 200 n.m. EEZ would take around 10 hours. More distant seasteads would require days of travel.
For the renewable energy advocates, there is an appropriate boat propulsion technology which is extremely mature, namely sails. The backup diesel motor can be replaced with an electrical motor. Several manufacturers already make electric boats, though they tend to be small, and it is not difficult to convert existing boats [ElectricBoats]. Still, the juice has to come from somewhere, and it does take a fair amount of energy to travel long distances.
Boats have a number of advantages. They are relatively inexpensive to operate, and reasonably quick for short distances. They can take many people or a large amount of cargo. However, riding in them becomes rather unpleasant when the weather is bad, and sometimes even dangerous. For long distances, they are a bit slow. Boats are the clear choice for cargo, and for transporting passengers over short distances. In good weather, for passengers who don’t mind a slow trip, they are suitable for longer distances as well.
As we mention when discussing the dock, transferring cargo between a ship and seastead may be a dicey proposition. Solving this problem will be a big factor in whether we can ship goods to a seastead, which is a big factor in how much it costs to import and export goods.
More distant seasteads may wish to fly people in and out using planes or helicopters. A several hundred mile trip would only take an hour or two of flight time, and even a seastead in the middle of the ocean should be reachable in half a day or less. While this method is much quicker, it’s also more expensive and requires more infrastructure. Seaplanes can land on the ocean, but only in very calm or protected waters. Regular planes require a long runway. Helicopters only need a small landing deck, however they are more expensive and dangerous than airplanes.
There are special STOL (Short Takeoff and Landing) airplanes which need less runway length (as short as a couple hundred feet). Our initial Seastead Lite design is large enough for one of these. However, STOL planes tend to have relatively low cruising speeds (120mph) and low passenger capacity (a few people). This makes it difficult to use these planes to transport resort visitors, unless the distance is short enough to allow many trips per day. Helicopters may be superior to STOL aircraft for this reason - the same amount of area as an STOL runway could be used to land many helicopters.
Groups of multiple seasteads make longer runways possible, at which point planes are an excellent option. Groups large enough to have a breakwater can have seaplanes land in their harbor, or have long runways. Before then, either helicopters or STOL aircraft can serve to transport passengers willing to pay extra for a quick ride, as well as for medical emergencies. Seasteads with protected waters can be serviced by seaplanes. Individual seasteads, far from land, without protected waters, will have to use expensive helicopters if they want to move many people.
Early, smaller steads will probably be towed into place and anchored, as that is the cheapest and simplest technology. Deepseasteads will likely use a combination of these methods, spending some time at anchor, some time drifting, and occasionally using active propulsion. They may also try being set adrift in the doldrums.