There are 6 different kinds of fundamental motion on a ship, some of these motions, like pitch and roll, or surge and sway, are basically the same but different only because they take place along the x or y axis of the vessel. On a seastead or oil platform there is no difference between the front and the back, so x and y axis are no longer distinct from each other. You can see the 6 different types of motion of a rigid body on water in the video below:
So from this video we can see, that when talking about a single square structure with no difference in shape between the front of the structure and the back, it makes no meaningful difference to talk about anything other than Pitch and Heave. But why do we need to know this information? Why is this important?
Let’s imagine that you were a scientist, and you had a tall beaker filled with sulfuric acid. You were about to conduct an experiment for science, and then the seastead you were on suddenly got hit by a large wave. Let’s imagine what might happen next, if the seastead tipped over 90 degrees on its side then everything in the room might go flying and you would be crushed by a bookshelf, if the seastead tipped only 1 degree, then there would be no noticeable change and everything would proceed as planned. But what if the seastead tipped 8 degrees? Or 12?
Image by Chokniti Khongchum
In his seasteading book, Joe Quirk proposed something called the ‘Wine Glass Test’ where one man would sit on a seastead with a glass of wine on the table, while another man would drive by the seastead on a boat and try to get it to rock around. If the wine glass remained on the table undisturbed, then the seastead design had passed the test and could be considered a success. This test was performed years ago with Ocean Builder’s first design.
Today, when arktide is assessing the stability of a potential new design, we will take both the Pitch and Heave into account. If a seastead pitches (or rolls) in the waves less then 2 degrees, this is considered very stable. If it bobs up and down at less than 1 m/s^2, this is considered acceptably calm. But what about Heave, why does that matter? Well to give an example, Earth’s gravity is about 9.81 m/s^2. The significance of this is that if you had a 200lbs person and they were on a seastead that moved upward in a wave at 9.81 m/s^2 they would temporarily feel like they weighed 400lbs because of their rate of acceleration, and on the way down they would feel weightless. At 1 m/s^2 or less, this person would only change their perceived weight by about 10%, akin to adding 20lbs on the way up and losing 10% on the way down. This might be slightly uncomfortable, but shouldn’t cause injuries even during very rough weather.
So now we know what a safe margin of movement is in rough weather. But what is rough weather exactly? Maybe you have always felt scared of the idea of a floating city because of Tsunamis, storms, or rogue waves. Well to start off, we can say that during either an Earthquake or a Tsunami, the safest place to be is by far on a seastead. They are naturally impervious to both of these natural disasters. An Earthquake has no effect at all, and a Tsunami does not grow to a large wave size until it nears the coast. In fact, most tsunamis are characterized by large wave periods, and low frequencies. That means boats and especially seasteads can simply roll over top of them as if they weren’t even there.
So the time during which a seastead is actually faced with danger is only during storms like hurricanes, or from rogue waves. As we mentioned in THIS blog post, there are many areas of the ocean which do not experience any hurricanes or typhoons, and so these areas are easily habitable. Waves just south of the Philippines only get to a maximum of around 4.25 meters in height each year, closer to the equator waves only get about 3 to 4 meters in max height. Near places like Singapore that are very shallow and coastal, waves can max out at only 2 meters at their annual highest. But waves up near Alaska can sometimes reach as high as 9 meters during their stormiest seasons. It is common that in colder climates where the air is thicker waves can reach larger sizes, and currently no seastead design is capable of handling those environments, though there are some oil rigs that can.
Arktide’s principle is to engineer for the most habitable zones first, and designs for rougher waters can be pursued after the more viable areas are already being colonized. That being the case, we decided to set the standard at 5 meters and try to make sure we could develop designs that would remain stable in those conditions.
So now we have our criteria; we want a seastead that will have less than 2 degrees of pitch and less then 1 m/s^2 of heave. If you remember our Evolution of Design blog posts which you can read HERE and HERE then you will remember that in the early phases, we were quite a long ways off from making those goals. But as time went on we got better, going from 12.5 degrees of pitch and 3.17 heave on our first design, to only 1.93 pitch and 0.347 heave on one of our last designs, the HEX1000. But as we went looking for warehouses to construct this new design in, we found that the dimensions of the structure were far too large to be accommodated by such modest construction locations. As a result, we had to change strategy yet again and developed the Minispar, which had a pitch of only 0.868 but a considerable heave of 0.835. After refining this design further and changing the way that it would connect with neighboring structures we finally developed our true final design, the ArkPad.
The ArkPad is made of smaller pieces like the Minispar, but a minimum of 4 must always be connected together to hold the upper platform separately, which is where the house is placed. Once all 4 sections have been joined you have the end result, the ArkPad, which has a final pitch of 1.66 degrees and heave of 0.611, both well within design parameters. After testing in standard 5 meter wave storm conditions, we decided to up the anti and test the ArkPad in 6 meter waves to see if it would remain structurally sound, and not only did it not take any damage from the waves striking the bottom of the platform, but the ArkPad’s pitch was only 1.73 with a heave of 0.680. A remarkable result, considering it wasn’t engineered to do that. In the coming weeks we will continue to run further tests on the ArkPad in Hurricane conditions, including high winds, and potentially testing Rogue Wave scenarios. Stay tuned for more!