The Seasteading Institute

A non-pressurized unit would implode faster than one with equal forces pressing out as in. If the air in a unit is at 15psi, and the water around it is at 36psi… what would happen to the structure if a leak occured?

How much more likely would a leak occur at all in a unit having these added stresses compared to a structure that was pressurized at 36psi to match its surroundings when it bumped into a reef… or a whale?

Where the leak occurs is very important.

The two different structures:

1. A flotation device that displaces the water with the rigidity of the structure, with one atmosphere of air pressure inside (i.e. unpressurized).
2. A flotation device that displaces the water with higher than ambient internal air pressure (i.e. pressurized).

Four scenarios:

• With a deep leak, near the lowest part of the structure, device 1 will not implode, but water will be forced through the leak dur to the pressure difference.
• With a deep leak, device 2 will not implode, and there will only be slow exchange of water and air through the leak.
• With a shallow leak, close to the surface, device 1 will not implode, and take on water only very slowly, depending on the size of the leak.
• With a shallow leak, device 2 will implode because all air will be forced out and the structure will collapse.

So those are the alternatives, as I see it.

Also, I would probably argue that a shallow leak is more likely than a deep one.

In addition to this, the pressurized device cannot be repaired from the inside if there is a leak (because there is nobody there).

Ok, that changes things. I thought you had a vertical container partly out of the water in mind:

http://wiki.seasteading.org/index.php/Image:Implosion.JPG

Your first drawing seems to lack displacement in the water plane. This is necessary (hence my vertical container). Looks very professional otherwise.

I’m also not sure what would prevent an implosion in situation 1, since there is high external pressure and low internal pressure. That is where I’d expect the structure to crush under the sudden strain

A boat does not implode even though the water pressure outside the hull is higher than inside. This is because the structure of the hull is strong enough to withstand these forces. You are trying to replace structural strength with air pressure. This means that if the air pressure goes away, the structure will fail.

But I guess we have been talking about different scenarios.

The container in my last sketch gets stability from a ballast (counterweight of lead or steel) in the bottom. This is generally called a spar buoy. Don´t pay attention to the superstructure, it is way too big . If you used four containers in a square as legs you wouldn´t need a counterweight. That would be a semi-submersible.

Displacement in the water plane – think of a cylindrical spar floating vertically. A narrow spar has low displacement, and a wide spar has high displacement. It is the area that intersects the water surface. If you have very little such area it will be difficult controlling how high in the water your vessel floats. Your design looked to me like all the buoyancy was submerged. The buoyancy would either float to the surface or the top deck would sink down and rest on the water.

I finished updating the drawing. The new design is certainly more complicated, but (hopefully) it manages to take advantage of the best aspects of both systems.

I haven’t shown the hydraulics or shock absorbers in the Sealegs (as I’ve become fond of calling them) yet but I think you can see from the elevation, the intended range of motion.

In short waves, the Sealegs will move up and down with the ocean, yet resist enough to keep the structure an appropriate height above the surface. It is hoped that while some of the buoys are forced upward by a wave, the rest are being allowed to go back down so that the combined average results in a smooth ride. The deep water buoys should also add to the calming effect be resisting vertical motion by its large area in depths where most wave motion is either horizontal or nearly non-existent.

In large swells, all sealegs at once might be forced upward, essentially acting as a raft at the bottom of the structure. The lower deck should most likely be sealable. With water-tight doors and non-operable porthole windows so that the structure won’t take on water and can act as additional buoyancy in extreme emergencies. Larger surface waves generally have longer wavelengths (except, perhaps, for rogue waves) and therefore should church much deeper water, making it so that the deep buoys don’t prevent the structure from rising with the swell as necessary. All the sealegs together should also do a decent job of keeping the craft’s head above water.

If we change the length of the sealegs, we could also hope to go further into shallow water, by raising the whole thing up, given calm enough water. In the current configuration I drew up, putting the sealegs at 90 degrees to the water (instead of the typical 5-45) would be able to raise the draft depth by almost an additional 10 feet from 53′-11″ to 42′-1″. Other configurations might be able to shorten the draft to the 35′-0″ or less required to enter many ports.

One last potential benefit of the sealegs would be in helping prevent collisions with other ships. It may be minimal but the devices could soften impacts from nearby ships in much the same way they soften the impact of waves in the vertical.

Another possibility I thought of was that of building an artificial reef on the deep buoy shelf. Remaining in calm costal waters long enough might allow a coral colony to form and other, smaller fish might conceivably be able to make a home here. A few questions come to mind with this idea. First, how long would it take to build up such a colony and could you simply “collect” members at each port you visit, without needing to remain stationary for too long? Second, could the fish keep up with whatever cruising speed this craft maintains and would the larger waves of the open ocean devastate such a community, or would the depth be sufficient to protect them? Finally, as a vessel with the potential of traveling great distances, would a mobile reef harmfully cross-contaminate species from different oceans or areas of the same ocean? [Zebra mussels in the Great Lakes.] The oceans are all connected, but inability to travel through colder waters around a landmass generally provides a sufficient barrier between ocean habitats. Is it safe to assume that regular ships would have done all the species cross contaminating already, or would this be a real danger to avoid?

Certainly, a seastead that intentionally builds a reef might be willing to remain in the same ocean to prevent this. It might also likely be true that a seastead without an intentional reef attached would only carry as many aquatic “passengers” as a similar sized ship might. Even so, it is an important question to consider before such a feature is added. In place of a reef, it might be logical to grow and harvest seaweed from the deep buoys, since it might be more directly beneficial to the seastead (rather than as a fish aggregating device). Another option would be to enclose the top and bottom of the deep buoys with metal grating or net for an open aquarium design. The current design would provide 4 such spaces at 8,900ft³ each.

Well, I know that building artificial reefs, though not very effective in the past, is quite successful in some applications. I was thinking more along the lines of Reef Balls, which I first learned about while watching ‘dirty jobs’, I think. However, this biorock idea is also quite interesting. Rather than simply piling reef balls on top of the deep buoys, it would be possible to run current through the metal structure long enough for a natural coating of minerals to cover the structure. I’m not entirely sure about that possibility, though, since it seems like even with a coating of minerals, the metal would then be more subject to corrosion than if they had an industrial grade protective coating on it. As a primary floatation device, it would probably be best not to risk it. However, forming metal mesh into a hydrodynamic and more natural looking form around the deep buoys and using this process could have some positive influences on cruising speed, impact protection, and fish aggregation. The Reef Balls would make great ballast material, though. With a range between 5,000lbs and 0.5 lbs, you could plan the ballast weight and location pretty precisely, as long as you keep in mind the potential for natural growth. [You might even need to put some removable ballast so you can drop artificial weight over the years without losing carrying capacity as the reef begins to grow)

My main problems/questions about the artificial reefs were if cross contamination of species between regions was of major environmental concern and how long an artificial reef would take to build. In other words, how long would we have to 'park' in shallow water for the reef to mature enough for open water travel and should we even create such thing?

I did a quick comparisson of 40' shipping containers to 1000 gallon propane tanks. Since propane tanks are rated for 250psi, they would already be designed for more pressure resistance than we would need for this application. They also usually have legs welded on that we could attach (bolt/weld) to if they were inverted underwater. Unfortunately, this comes at a premium. I did some calculations to compare their buoyancy lift and price, by calculating price per pound of lift for both. Even when I double the shipping container cost ($7,000 -- $3,500 is already conservative with most new containers costing only $3000) and use the lowest price I could find for propane tanks ($2,200 for a 1000 gal. model -- one manufacturer charges $4,013) the difference is vast. Propane tanks rate at $0.36/lb while shipping containers come in at $0.05/lb. On top of that, the rounded tanks might need additional support structure to keep them in place. I guess the question is whether we could get sufficient strength for a good safety factor within the $7,000 budget for extra layers of interior reinforcing/metal sheeting/industrial coatings. Of course, to match the propane tank in price, we could spend up to $92,000 each... though that much extra metal would reduce the efficiency and the price point comes down much more quickly. So, with that unpredictable curve (not enough info), I'd still guess that a shipping container would beat propane tanks. The question remaining is, how much will it cost to get to upgrade to an appropriate safety factor and if pressurization plus minor reinforcing and puncture protection is good enough to achieve the desired results.

[Again, I like numbers too much sometimes and shouldn't have bothered going into so much detail on limited information, but what's done is done.]

In the design above, I’ve begun thinking about space planning. Normally, a 14,400 sq.ft. (3 floors) house is a mansion and even 4,800 sq.ft. is 2-3 times the average… but you’ve gotta remember that this place isn’t just a home anymore, it’s also partial infrastructrue from an entire town. So, I’m thinking that a large portion of the lower deck would need to be reserved for storage, large fresh water storage tanks, important machines and equipment for various aspects of life support. The central deck would be the main living space. It might need to give up some room to any equipment that requires more than 9′ of height to function, but it would still leave quite a comfortable area (so far in the design) for living. The top floor, since I didn’t label it in high detail on the drawing for you, would be a greenhouse.

You might ask why one would need a greenhouse in tropical climates, where most seasteads might hope to stay in. The answer is high wind and sea spray. If you’re going to grow anything that isn’t salt resistant, it would probably be a good idea to protect it from the massive amounts of salt all around. If you use crop rotation and stagger plantings year-round, you might hope to have a constant supply of fresh vegetables all year, even if you can’t eat some at every meal. If you plant once per month, twelve times per year, you might also hope to harvest each crop once per month. A quick calculation using the suggested seed spacing for sweet corn can give us a small idea of what this might look like:

average seed spacing of 22 inches between rows and 10 inces between plants, gives 1.53sq.ft. per plant. Assuming 50% crop loss: 24 cobs of corn (12 edible) per month times 12 months equals 288 cornstalks. At 1.53sq.ft. that’s 440.64 – - > about 450 square feet for corn production. With 25% of the greehouse (unfortunately) devoted to walking and working room, that leaves 3,600sq.ft. of plantable area. A year supply of corn would take up 12.5% of the arrable land on board. If other crops are equally land-efficient (I doubt it) then you could plant 8 crops for year-round consumption. Now, a natural season doesn’t take a full year, so crop rotation could utilize that land 1-3 more times within a year, increasing your crop output substantially. This doesn’t sound like such a sacrifice… if my numbers aren’t horribly miscalculated.