DRP #4: Breakwaters
December 15, 2008 at 6:53 pm #771
A free floating breakwater would allow people to float less sea worthy structures on the inside without having to worry about extremely harsh ocean weather. Are large free floating breakwaters economically feasible?
Given the approaching holidays, this topic will be two weeks long.December 15, 2008 at 8:13 pm #4482
Howdy all. I will be moderating the Breakwater discussion, as it is something I am very interested in. A good place to start is to review the breakwater section of the book, which is short.
Let me briefly pitch why I am so excited about breakwaters. Our initial CoastStead design costs about $150 – $200 / square foot. With maintenance costs, this is something like $20/ft^2/year leasing rates. This is cheaper than San Francisco Class A commercial real estate, by a little bit. But it is still quite expensive. The only businesses that we’ll be able to support are those which can afford to pay commercial real estate prices in major metropolitan cities. I think there are enough of these businesses to make such a venture worthwhile, but it will be at a relatively small scale – tens to hundreds of thousands of ft^2 initially. (a few acres).
Breakwaters have the potential to dramatically reduce costs, if the cost of a breakwater scales with it’s length. A circular breakwater has length 2*Pi*R, while the area it protects is Pi*R^2. That means as we increase the size of the circle, the cost per unit area goes down by 1/R. However much a breakwater able to stop ocean waves costs (and it may be quite a bit), we can reduce our costs by a factor of 16 just by quadrupling the radius.
While this may make for enormous initial capital costs, just think about the dramatic difference between opening a business park 20 miles off the coast of San Francisco with office space leased for $24/ft^2/year (so $2000/mo for 1000 ft^2), and opening a circular mile of open ocean with calm water leased for $1.50/ft^2/year ($125/mo for the same 1000 ft^2). In the former case, you get a few high-valued businesses like medical tourism. In the latter case, it’s like you are opening a new land mass for colonization. It is so cheap that people from all over the world can come there and start building a new society. It’s like the difference between getting sovereignty over one office building or a large tract of land.
Designing a cost-effective breakwater that scales with length may not be easy. But that’s the size win we are talking about.December 15, 2008 at 8:38 pm #4483
There are lots of designs out there, and I hope y’all will post them here and investigate and summarize them. I just want to present my own design for feedback. It looks something like this:
- The wedge should be lower in the water
- Slope should be much shallower, as the length is many many times the height
- Rather than being a solid wedge, just imagine the top (slanted) surface as a single sheet
- Rotate the sheet in a circle to form a complete breakwater
- In other words, imagine an annulus, with the outer edge a little lower in the water than the inner edge.
This is based on the same principle as a coastline. As waves approach a gentle slope, they “pile up”, decreasing the wavelength and increasing the wave height, until they break. When they break, they dissipate their energy harmlessly by smashing into themselves, thus we avoid needing to build a breakwater which can take the enormous force of a wave. Features:
- Wave motion goes below the trough of the wave, falls off as square root of distance below wave. We need to start well below the troughs of the biggest waves – say several times the wave height in depth.
- Wave length for open ocean waves can be huge, like a thousand feet. We need to be many times the wave length, so at least a mile, perhaps several miles long. (Hey, I didn’t say this would be easy!)
- Because we are gently nudging the waves along a long length, I think the material can be very thin/week – like a thin sheet of plastic. (reinforced occasionally, perhaps).
- I have a design which requires only stiff elements being 2 rings, for the inner and outer diameter of the slanted annulus. The outer ring has several miles larger radius, and is located hundreds of feet lower in the water than the inner ring. Connecting them is a huge sheet of plastic. The outer ring is weighted. This will keep the breakwater in tension without requiring any stiffeners on the sheet.
- In other words, this is a tensegrity structure. We have 2 compression members (rings), and a huge tension member (plastic sheet).
- The structure is robust to small tears and other damage, because it is a cumulative effect over the entire structure. Each bit only takes small forces, and no piece is essential to the overall effect.
- The rings can be expanded incrementally to increase protected area. The sheet can too, although it is a bit more difficult.
- Inside the breakwater, simple hollow concrete boxes will be used as building foundations.
- The breakwater will create waves that can be surfed!
Yes, the plastic sheet is enormous, but this structure is really not that expensive! On Amazon, 800 ft^2 of 6mil black plastic is $66, That’s 8.25c/ft^2, or $2.3M per square mile – and that’s retail cost. Here is 4mil for $1.2M/square mile. Suppose we protect a 2 mile radius with a 2 mile annulus. Then our breakwater area is Pi * (4^2 – 2^2) = 38 miles^2 , while we are protecting 12.5 mi^2 of calm water. At $1.2M/mi^2 for black plastic, our 38 mi^2 will cost $46M, but it will be protecting 350 million square feet of open water! That’s 13c per square foot protected. Compare that to the $100/ft^2 cost of protecting buildings by lifting them out of the water on big spars, as oil rigs do, and you can see why I am excited about this idea!
- Wayne believes that the strength of a breakwater may scale as the area protected, and thus the cost. I don’t understand why. The wave energy is proportional to the cross sectional area, which scales linearly with radius.
- We need to somehow connect the breakwater and the floating structures it protects, so they don’t bump into each other. This will require increased structural strength from the inner ring, perhaps some kind of cabling which buildings attach to.
- ? You add your problems here.
Comments / ideas / sketches / 3d models welcome!December 16, 2008 at 2:17 am #4484
Another way to avoid waves would be a blimp.
An article mentions airsteading as “a more flexible version of seasteading” yesterday:
On the cartoon Lazytown the “slightly above average hero” Sporticus lives in a blimp:
Now I think I will be able to afford a seastead many years before I could afford an airstead, but at some point I do think it will be affordable for some. Anyway, I think it is an idea worth mentioning.
If you were not having to follow regulations, you could use hydrogen. Maybe design where the living area could parachute away if the blimp caught on fire, or something. With weather prediction today we should be able to avoid storms. A blimp has plenty of room for solar panels. Easy to have lots of living space. Without helium, the cost need not be too high.
— VinceDecember 16, 2008 at 1:00 pm #4488
Something like this?
How much water can you put on this before the plastic sheet breaks?
How do you repair it when it does? Can you walk on it?December 16, 2008 at 1:13 pm #4489
Waves start getting steeper on a shore when the depth is lower than 1.3 times their height: it is not dependant on the wavelength (except for wavelength being seven times the height in fully developped waves). This means your breakwater concept can be made significantly smaller than what you’re expecting !
On the other hand, the flat section of the breakwater would be subjected to vertical stresses equivalent to the horizontal forces of the waves (mechanical energy being transported in a forward-rolling circle). I do not think simple plastic fabric would resist it. If you use two layers of fabric (one sloped, the other not) that deform under the stress instead of resisting it, however, there is a neat little thing you might try: adjust the width and depth of the breakwater so that it cuts the waves at their half energy depth, then dephases them by a half-wavelength, so that as they passe the breakwater, the top and the bottom halves of the wave would cancel each other.
It might be cheaper to build an emerging wall closer to the seasteads using some raw solid material (fiberglass concrete encasing polyurethane or polystyrene foam) that would simply resist and reflect waves’ energy. This marina in SF has had floating concrete breakwaters survive every storms so far. Empty boxes of concrete (lined for water-tightness ?) may double as storage for fluids or grain, too.
Also: on your two rings + fabric design, the outer ring would be working in compression, but the inner ring would be working in tension and thus would have to be a tensioned cable and not a rigid ring in order for the structure to transmit the efforts tensegrity-like. Il ike this concept, and it sounds modular too as one can probably unconnect it at one point and add elements to scale it up.December 16, 2008 at 4:44 pm #4490
To decrease the risk of Hindenburg-esque disasters when using hydrogen you could instead hang your residence from several hydrogen balloons, separated so that one can burn without igniting the others. Then you just need to inflate a spare balloon before you hit the ground.December 16, 2008 at 5:21 pm #4492
The core of your Dynamic Geography paper as I see it is that more mobility => more freedom.
Spending time designing large breakwaters => better large breakwaters => less mobility because the advantages are only gained if you stay (trapped) inside a large breakwater => “High Cost of Switching” and “High Barrier to Entry” => less freedom.
Wouldn’t it be better if TSI focus solely on a design (spar, waterwalker or something else) that can cope with large waves instead of designing something that tries to remove the waves in a specific location?December 16, 2008 at 5:24 pm #4493
Image is incomplete, needs joints and such, but you get the idea.
A circular cross section is tough, so you can minimize material use.
Water entrapment inside adds mass, but costs nothing.
Simple, modular construction. Make a cylindrical hole in the ground and you practically have a finished mould.
Easily repairable. Just disconnect broken tubes and add new ones.
How to get correct buoyancy (add styrofoam pieces in mould perhaps?). Or use another material than concrete?
How to join them cheaply and securely, and with some kind of bumper so they won´t destroy each other. Ideally when connected the tubes should strive to become a straight line. Then they will work to keep a nice circular shape when connected in a circle.
Maybe not feasible for ocean sized waves…December 16, 2008 at 11:15 pm #4494
How about combining wave breaking with power generation?
Or another idea:
Of course placment of turbines could be changed to make service easier.
And the connection might need a pivot point in the center.December 17, 2008 at 2:01 am #4495
The 9 foot marina model I made could open up and so move like a 30 foot snake very easily through the water. Video of tests at wiki page below.
A marina lets small boats that would not be comfortable/safe in the deep ocean be safe and comfortable. When the weather is nice they can go outside the marina or leave altogether.
A marina also makes it easy to move between boats. Both people and cargo, Trade now becomes easy.
I think if we had like 50 families with boats that a floating marina could be very reasonable. But I don’t think it is the easiest way to get started. I still think single-family-seasteads will be the starting place.
Might be nice to have a special boat designed so that the back of the boat could attach to the inside of the breakwater/marina wall.
I am confident that a 200 foot diameter marina could float up and down with the major swell and stop the small waves. This would let smaller boats, say 50 feet long and 15 feet wide, have the motion and comfort of a 200 foot wide marina. So I don’t think there is any real need for the breakwater to stop all the waves, just enough to make things comfortable. You just want the boats inside the marina to move together and not bang into each other.
If the idea is “floating marina” then I think it can be done. If the idea is a breakwater that stops all the waves, then I think that is not going to happen anytime soon. Some waves go down hundreds of feet. So I think it is better to think in terms of “floating marina” than “breakwater”.December 17, 2008 at 1:23 pm #4497
Funnily, I came to seasteading because my original dream of airsteading was too “extreme”
A slow-moving blimp with distant, long-tethered gas bags is also ideal for harnessing atmospheric electric power. And dihydrogen can be produced while in the air with a condenser and an electrolyzer.December 17, 2008 at 2:16 pm #4498
Yes, making up for hydrogen losses from water in the air is a fun idea. I don’t know about harnesing lightning in a hydrogen balloon, might be something wrong with that idea.
Imagine a long beam with 10 balloons tied to it and the living area suspended from the beam. If we loose one baloon the living area could move front/back so that it was still below the center of lift. To make up for the lost lift we could:
1) Inflate the other 9 balloons more
2) Drop some water ballast that we had for just such an emergency
3) Turn propellers so they pushed down and made up for the missing lift
4) Inflate another balloon
5) Go down at moderate speed while working on 1-4
If the 10 balloons were in a line at the same height they could sort of draft each other as we moved forward. So while not nearly as good as a blimp with a single cover, drag might not be too bad, at least at a slow enough speed. As in a seastead we are willing to sacrifice speed for other things.
Being on the ground, landing, and taking off are probably the most dangrous times for a blimp. A blimp hanger would be expensive and tie you to a certain location. So it would be fun if it never landed. But then there is the question of how people/cargo come and go. This might be with a small blimp or even a bi-plane. But this is added cost and complexity either way.
Again, seasteads first and blimpsteads later. But fun to think about.
— VinceDecember 17, 2008 at 2:45 pm #4499
Tether the blimp to a buoy in the ocean. Then send people and goods up on a lift on the cable.December 17, 2008 at 11:01 pm #4500
Wouldn’t a http://en.wikipedia.org/wiki/Kelp_forest be a very cheap possibility to dampen waves a little?
If it grows (i haven’t done much research) on ropes that are attached to the bottom or top of the Seastead, it could also stabilize the Seastead directly if the forest is deep enough not to be moved by the waves, or the forest is bigger than a few wave lengths of the biggest waves.
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