If we want to create a Very Large Floating Structure, VLFS, in the open ocean, and as commented in the previous blog, we need a type of structure that attenuates the waves. Semisubmersibles are ideal for that, as in the MOB. But other ideas and technologies are also being developed. The very well known Pneumatically Stabilized Platform, PSP, is a very promising structure.
The PSP, designed by Float Incorporated is a type of pneumatic platform composed of a number of cylindrical shaped components packed together in a rectangular pattern to form a module. Each cylinder is sealed at the top, open to the ocean at its base, and contains air slightly above atmospheric pressure. Most conventional floating platforms acquire their floatation forces by directly displacing the water with their hulls. However, the PSP utilizes indirect displacement: the platform rests on trapped air that displaces the water; the primary buoyancy force is provided by air pressure acting on the underside of the deck. The water in each cylinder moves up and down, and the air pressure in the trapped airspace changes. These spaces are connected through pneumatic lines and valves, so that these pressure changes result in air moving between cells. This dampens the waves and distributes their force in order to reduce peak load on the structure. If air turbines are attached to these lines, it becomes a wave-powered electricity generator.
The PSP has some characteristics of a platform (it can support loads) and some of a breakwater (it attenuates waves). It is built out of concrete, very modular and fairly reconfigurable. However, the design for a floating airport off the San Diego coast was rejected in 2003 as too expensive, so it remains an unproven technology.
The original idea came from the Wave Pumps developments thirty years ago. The main advantage towards seasteading designs is that the problems of energy source and wave attenuation can be solve at the same time (if we are in an area where we have enough waves to produce the required energy for the seastead).
A similar idea for attenuating wave movement is developed in anti-heeling and anti-rolling systems with tanks of the active/controlled type, where the water flow between tanks is controlled with automatic valves. This technology is currently used in ships to avoid the roll movements and not for the heave movements as in the PSP. But in any case, it is a recent but proven technology and not very expensive. So perhaps we could expect that in some years, the PSP could be commercially profitable, because the structure itself made of concrete seems not to be the problem.
The main advantage towards seasteading designs is that the problems of energy source and wave attenuation is solve at the same time.
You would need continous waves of a certain size for that. Just like wind power, which cannot be relied on for base load power. Sometimes the wind doesn’t blow, and sometimes the sea is calm. I agree it could probably help the energy situation. But solve it? Remains to be seen.
Also, the drag of such a platform could be more than that of a simple barge (VLFS). This can increase station keeping costs.
And you cannot use a lot of the space inside the structure as real estate, like you can with a VLFS. Again possibly increasing cost per usable space.
I agree the design is worth looking into though.
A simple square flat float of 50m diameter is sufficient stable to allow comfortable living in the high seas – this is not theory – this is happening as we speak.
So what is this never ending quest for elevated platforms and complicated and expensive tech concepts for wave attenuation – those are all concepts that where in discussion BEFORE the Nkossa Barge was implemented 60 km off coast – does anybody ever update the paradigmas according to the newes installations of the offshore industry ?
Or are we stuck with texbook knowledge that was in discussion some 20 years ago? – Is this “lust of overengineering” just a shyness to step into the so much needed practical part and start doing it.
A concrete flat float will do it when it is big enough ! The world knows that already – the industy is applying that already – why is TSI insistantly ignoring that fact ? – trying to solve imaginary problems that have been solved some 20 years ago.
Nkossa Barge flat float, chambered, built in concrete.
width 46m lenght 220m height 16m draft 10m – currently 160 people living there miles offshore – permanently – service life expectance 200 years
Usable volume 27.000 cubic meter – owner Elf Aquitaine
Floating on the ocean since march 1996.
Cost ( French Fr4.7billion)
Does it rely on elaborate anchoring to maintain stability, or would it be just as stable with just a propeller keeping it parked in roughly the same area?
I like the concept but a lot of the big oil industry floats and spars use extensive anchoring systems that aren’t very flexible and probably very expensive.
Carl, Ellmer:
The idea of the blog post is only to show all the possible structures and technolgies that could help to future seasteads, and obtain the feedback of community members, like you are doing. But it does not mean that any structure presented here is the “definitive” solution.
Carl, regarding:
1.- Energy obtained from a PSP, you are right, it can help to solve the problem. I have edited it again.
2.- Drag and keeping positioning: I am assumng that if FPSOs use DP systems, a PSP could also be kept in positioning with DP. Remeber previous discussions about that in this blog post.
Ellmer, regarding Knossa barge, as far as I know, it was permanently anchored in a 170 m water depth in 1996, in the west coast of Congo, in West Africa. That means in calm and shallow waters, that do not suit exactly the requirements of international waters. And I think that there has not been built any other concrete barge of similar dimensions up to the moment. There are some projects/studies for using them as FPSOs and for floating LNG plants, but they are still projects and most of them as moored barges, as far as I know. Also the MOB projects in concrete are insteresting, as introduced in previous blog.
In any case, I am agreed with you that concrete barges could be perfect for a seastead. A solution could be a concrete barge with dynamic positioning.