Mobility

Seasteads can be classified by three levels of mobility:

Fixed

Seasteads which are built on a fixed foundation (sealand), or anchored is a way that is part of the design (Tension Leg Platform). In general, these types of designs are considered neither practical (depth) nor desirable (Dynamic Geography)

Floating

Global position is kept either by virtue of geograpical location (gyre), or by means of anchoring. In case relocation is desired, specialized equipment (tugboats) are hired. Position relative to neighbors is best kept by means of connections between individual seasteads.

Propulsed

The seastead has its own propulsion systems. They should be at least powerful enough to maintain a time-averaged position, and powerful enough to avoid collisions with nearby seasteads.

Economies of scale

It should be noted that mobility on the water is subject to strong economies of scale (Fuel consumption as function of size) For large seasteads, the cost of fuel is likely to be small compared to other expenses (see: flotel data). For seasteads on the small side of the scale, these figures are probably very different, especially if the design under consideration does not optimize for weight and hull shape, the way boats do. At present, little information is known on the subject; existing data generally does not deal with the hull shapes and low speeds we are interested in; getting good estimates is the subject of present research.

Economic Estimates

Slow moving blunt object: experimental

To get a rough estimate, the figures in this article are useful. A 3250m³ blunt object is dragged at an estimated speed of 0.5 knots, requiring 12.4HP or ~10kW of electricity input, or 36MJ/h. If said electricity was generated by a diesel generator, that would amount to 3L of diesel an hour at 1/3 efficiency, or two tons of diesel fuel a month.

The displaced volume is in the same range as some of the designs under consideration, which intend to house several families. 0.5 knots might not be enough; finding a place with currents limited to that speed should be possible, but that does not include wind-induced loads, which are likely to be dominant under most circumstances.

Clubstead

Overall, it is not certain that continuously propulsed small seasteads will be economically viable, especially given the uncertainty in future fuel prices.

Comparison

The costs of the various options strongly depend on a variety of factors. In shallow coastal waters, anchoring is cheapest by far, and there is relatively little room to drift.

In the open ocean, anchoring may be prohibitively expensive, and in many locations, a low-powered system might suffice to maintain a position within some region.

A seastead continuously operating at cruise speed is certainly not economically viable on the small scale, and probably expensive even for large scale shipsteads. Besides the fuel costs, continuous mobility around the globe might not be as good as it sounds at first. While nice for vacationing or retired people, most jobs are dependent on being tied into existing economic and social networks. It is assumed that a good measure of stability in geographic location is necessary for economic viability.

There are various speculative options with regard to mobility.

• Strike a deal with the host nation, not to regard anchored seasteads as permanent installations; or establish a precedent to that effect.
• The seasteads are self propulsed, to avoid being classified as a permanant installation. It is not clear if this is a possibility.
• Find locations, bordering the EEZ and continental shelf, where anchoring is affordable. For legal reasons, anchoring within these zones dramatically extends the claims the host nation can lay on the seastead under international law.

None of these have guaranteed succes though. The safest route is thus:

• When operating within the EEZ, anchors are used, and these legal compromises are accepted as a necessary transitionary stage
• When moving out of the EEZ to international waters, there is more choice of calm locations, and plenty of room to drift around.