BreakwaterBay

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Description

Use a circular breakwater to shelter a disc-shaped bay from the waves.

Detail

Because this affects so many of our requirements, sometimes in conflicting ways, we'll discuss the tradeoffs here:

• Comfort - By eliminating waves, interior structures should be very comfortable
• Safety - By having a single tough structure to eliminate waves, we keep the whole community safe. However, this means that if it fails, everyone may be screwed.
• Cost - If breakwater cost scales proportionally to its length, while it protects a space proportional to its area, then there is an economy of scale of 1/r. This means that it will get cheaper to protect each new unit of area as the community gets larger. However, a breakwater is a huge structure, and the initial cost is quite high, so it may not be possible to start small.
• Modular - Within the bay, floating land can easily be rearranged. However, because of economies of scale, there will tend to be few breakwaters, and so it decreases the modularity between communities. To compete with an existing breakwater, you must build a large enough breakwater to be price-competitive. This reduces dynamic geography, especially in combination with the positive network effects of concentrations of people.
• Cargo - By creating a sheltered bay, this becomes very easy. (There needs to be a way in, of course).
• Scalable - While a breakwater doesn't scale to tiny very well, it scales easily from medium to large to huge, by inserting new segments into the ring.
• Mobile - A free-floating breakwater is mobile.

When analyzing a breakwater, Jesrad warns: "According to what I recently learned on breakwaters and wave mechanics, such a low scale is not accurate: attenuation of waves depends on wavelength and the location and height of the breakwater: the energy of a wave is spread on a height of water equal to half its wavelength, so obstacles in this zone are hit by the moving water and brake the wave. In your case a lot of the energy was simply moving below the model because the wavelength is too big relative to the height of the waves and height of the model." You can learn a bit about breakwater geometry and analysis at http://www.artificialreefs.org/ScientificReports/Wave%20reduction.htm

Variants

There are many ways to build a breakwater. We need to find a cheap, rugged, reliable one.

Vince Cate's Tensioned Ring

• Vince's page links to videos of tests: http://www.floatingislands.com/wavebreak/ninefoot

Patri's Aikido Design

• This is just a submerged, angled plate, or to surround an area, a submerged annulus with the outside circle deeper than the inside circle.
• It simulates the continental shelf - as waves approach it, wavelength decreases and wave height increases, until the wave breaks.
• Making the wave break, instead of hitting something, means the dissipated energy is absorbed by the wave itself, not our structure.
• My intuition is that this sort of aikido-like design will get you the biggest effect for the least materials