Current Loads

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With regard to station-keeping of a seastead, it is important to know the magnitude of forces that a seastead may experience due to currents.

This analysis depends on various assumptions.

  • The drag on a body strongly depends on its shape. Unless the seastead design under consideration is essentially a boat, data from boats is not applicable. Here we will consider various blunt bodies, such as cylinders and spheres, which should provide a decent approximation for many seastead designs.
  • The overall scale of the design under consideration is another important factor. It influences both the drag forces, as well as the amount of people to split to fuel bill with. For instance: clubstead carries 200 passengers, in a 20.000st structure, which is a 100st per person. From a different perspective: 50lb/sqft of indoor space is used, where this is about 1/3 of total weight; the rest is structural and ballast. This figure depends on the type of design, but 100ton/person does match some estimates from other designs. For smaller seasteads the ratio is worse however; we will work with 200tons per person.
  • Currents generally do not exceed 5 knots, or 2.5m/s. It is assumed that by choice of geographic location, the type of current encountered can be kept down to a maximum of one knot, or 0.5m/s.

Existing datapoints:

  • This article contains useful data. 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.

This displacement should correspond to 16 people. 0.5 knots is only hald the calculated maximum value, but it might be a good average. If 1 knot is desired continuously, that would imply a fourfold increase in fuel costs. As far as currents alone are concerned, the expenses extrapolated from this data a high but bearable.