Landluber's Guide to Seasteading Feasibility

(Theodore M. Amenta) #61

Spark: We are working at different scales — You are focused on boats. Good. Bravo! I agree. I am not however myself. I am trying to conceptualize a floating city. ---- 300 plus people with work and leisure activity. I am willing to help you. I am actually drawing a single family hexagon notion at this moment — based on Larry G drawings — but this is not my focus. I am trying to create the Seasteading Institute of a self sustaining community — TOUGH ---- They did not yet do it. ted

(Larry G) #62

Partly. I think most villages arise at cross roads. Cities develop from the most useful crossroads. I have seen very few cities, or even towns designed and built in one move. The “ghost cities” in China are an instructive cautionary tale. Developers often build suburbs in one fell swoop, but this relies upon demand from nearby population pressure to justify.

I think if you want to have a village, then you need to start with some way for individual houses to be built there and added later on. You could build a number of houses at one time and try to populate them. Or you can make the design for affordable houses available and point out where you’ll be if people want to join you with their own. Whether they join you with a hexagon or a sailboat. But I don’t think that designing a condominium automatically equates to creating a village, no matter how attractive it is. I think a cluster of individual homes gives more of a village feel to it. But I am curmudgeonly and don’t like neighbors.

This is with all due respect, Ted. I think you’re doing a great job at constructively adding to the conversation. And perhaps an experienced architect such as yourself can sell the idea to a developer of means more easily than a bunch of forum denizens.

Another factor in the hexagon village concept is individual ownership stake. I like the idea of co-operative businesses for seasteading, because it gives structure and ownership equity. If you can put the capital investment within reach of middle class families, then they can figure out the rest.

(Larry G) #63

We got cross-threaded a bit:

In my notion, the hexagon has an internal deck slightly above water level. It has walls that extend above and below this. Height is somewhat irrelevant but for the moment, consider an average height of 20’ overall, with half above deck and half below. The underwater portion has an open bottom. The deck is supported by sealed blocks of Expanded Polystyrene (EPS) foam also known as styrofoam, providing buoyancy. The mid-point deck provides structurally integrity, and the top is covered by a “weather deck” that supports superstructure or living/working space.

Should the water tight integrity of the shell between the lower deck and weather deck be compromised, there is no worry because the EPS positively displaces, unlike a hull enclosing empty space.

The multiple hexagon configuration is merely a means of attracting population with single family residences. By using hexagons in a modular fashion, individual units become affordable and cost-effective at the individual family level and become an asset with ownership equity. Clustering them provides for some off-loading of common functional needs like freshwater storage, waste treatment etc. to dedicated hexes (either publicly funded via “taxes” or by service subscription to a business that owns the hex. Variable configuration within the basic size and shape restriction allows for better fit to purpose as well as aesthetic variance. For example, your hexagon could be taller or shorter than mine (above water or below) and still fit into an overall village design.

  • By using a substantial straight edge, a robust mechanical connection can be achieved (better than corner->corner connections or round shapes).
  • The hexagon shape naturally lends itself to multiple units connecting to each other in repeatable patterns while also achieving considerable trapped or en-trained water space.
  • Hexagons packed densely have good structural strength against wind/wave loading or tow operations (being pushed by a tug).
  • The semi-irregular outside edge of a shape formed by multiple hexagons lends itself to greater linear edge than squares or rectangles of the same area, and better interruption of wave patterns than longer, straight edges.
  • Nature has few straight lines; biomimetic design of artificial ecosystems benefits from transition zones and irregular edges. Shellfish aquaculture and similar activities will benefit for the point above as well.

:slight_smile: On which point(s)? I am willing to be educated as well!

I expect that Cay Sal Bank is not a particularly high wave action storm area, with average depths in the realm of tens of meters or less.

For an example of value of property even close to the water’s surface, check this link. It is designed to show what happens if water levels rise X meters. For our purposes it can show the amount of land within X meters of mean high tide. I have set it to 3 meters, so everything in purple on the map is less than 3 meters above mean high tide.

As it shows, approximately half of Williams Island in the Bahamas is less than 3 meters above water. This 180 acre island was listed for private sale for over 20 million dollars in 2011.

I believe a large part of the population of the Caribbean lives only a few meters above water.

Anyway, earlier in this discussion I threw out a few numbers for a small-ish hexagon simply for comparison purposes. It could easily scale up. I believe the basic design and construction of the hexagon H-shell could probably double or triple without significant additional engineering and fairly linear increase in expense…

Small steps in the right direction
(Bob LLewellyn) #64

Also we can put a wave inhibitor wall around the boat marina which is on the lea side of the island barriers. There are ways to make the wave energy work against itself.

There are some places in the Sal Bank that are over a hundred feet deep but most is as you say around 40 feet or so.

(Larry G) #65


OK, so double the hexagon size to 50’ per edge. Double the size adds perhaps 50%-75% more cost? (Since labor is a good chunk of the cost and materials probably less so.)

Add hexes in stages, starting with an initial build (colored in green) like a “C” shape with the opening leeward. A phase two build (purple) starts adding a tail to improve the enclosed harbor area, trailing leeward as you add. So far, the green and the purple add up to the same shape as above. The dimensions are less important than the ratio as long as the construction technique doesn’t have to vary much.

Once you get to a certain critical point, it makes more sense to add to the outside of the hex ring than to create more “long, skinny” harbor. Thus phase three in brown.

“High Rise” buildings go to windward (for relative meanings of “high”; perhaps 3-5 stories?) Critical infrastructure gets built in Phase one, and probably suffices through phase two, but gets redundant and distributed additions during phase three.

Does it make more sense when it’s more fully fleshed out like this? @tamenta

New hexagon dimensions:
50’ each edge
100’ point to point
86.6’ flat side to flat side
300’ perimeter
6495 sq ft per hex
Phase 1 surface area: 65,950 sq ft
Phase 1 enclosed water area: 58,455 sq ft
Phase 2 surface area: 110,415 sq ft
Phase 2 enclosed water area: 84,435 sq ft
Phase 3 surface area: 175,365-260,000 sq ft

Boat Scale:
Larger ones depicted are approximately 90’
Medium size approximately 65’
Smaller ones approximately 50’

(Larry G) #66

There are significant stretches of shallows where commercial shipping or cruise ships can’t go, less than 20’ in depth. Such that there is serious danger of such vessels grounding during storms or low tide, forget about monster waves.


Actually, waves build going over such things…

(Larry G) #68

I’m saying regardless of whether waves are a problem or not, you have a serious issue of potentially grounding a vessel of any significant draft due to waves or tide, a more significant danger than wave overtopping. Because if you drop 5 feet due to changing buoyancy, but only have 2.5 feet f water under your keel, you are going to hit HARD, and either due damage of even injure people due to the impact.

But otoh waves can not get so big in shallow water without tsunami conditions.


Was reading it as ideal place to avoid larger vessels. I see your point about grounding, though. Sailboats with fixed deep keels might hit anyway… Storm surge and storm tides could be a problem, as well.

(Larry G) #70

In thinking about Cay Sal Bank particularly, I’ve been envisioning some sort of winch-assisted slipways for docking solutions being built into the seastead.

When looking at securing loads, slippage is problematic. You don’t want heavy things to have any play to build momentum and then be abruptly stopped. That causes damage, and often exceeds tensile strength of tie-downs. If you can just prevent the load from moving at all, you’re better off. ‘Beaching’ boats up a slipway above tide and wave surge would be one way of preventing damage during weather. Wind loads can be vicious but simply don’t have the same mass as water and aren’t quite as variable (or at least cyclic), so it takes massively more powerful winds to do the same damage as relatively minor waves can do, pounding on things over and over in a cycle.

You can only tie boats so closely/tightly to a dock. They need a little play because of water movement under the hull due to waves and tides. If you tie too tightly, you put undue stress on cleats and attachment points when water level drops or rises. But conversely, you also get the hull banging against the dock, and pneumatic fenders can only do so much, they sometimes slip out of place up onto the dock instead of staying between dock and hull. Or they can be crushed flat with enough force.

Even for fairly large boats, you could engineer a slipway that tilts to accept a boat, and lifts to store it level, out of the water. I would use some kind of lock and fill system to use water weight for counterbalance instead of hydraulic rams for ease of maintenance and long term lifecycle. Perhaps you could even build in carriages on wheels/rails that accept a boat hull like a boat trailer does for smaller recreational boats. Something like a light-duty railroad car designed specifically for cradling boats.

Also for Cay Sal, I still think a gravity base makes more sense than permanent flotation. The Hex “barge” with open bottom concept lends itself well to semi-submersible. If mobility and flotation is required to get buy-in (both economically and perhaps legally to get permission to operate in the region, and to remove the structures should the effort fail to catch on or continue) then float the things out there, and then ground them in an ecologically sound manner/place by removing some of the flotation. It’s pretty easy to figure ways to pull EPS blocks out from under the thing, and it doesn’t require absolute water tight hull integrity to re-float the hex in 50 years.

Casino barges in Biloxi Mississippi are floated in literally inches of water depth, to get around legal rules requiring gambling operations to be contained on boats. They are permanently moored to buildings with an internal connection between the barge and the hotel building, often on multiple stories of the hotel, that the average person never even notices when they walk over it. For serious storm conditions, they temporarily scuttle the barge (flood the buoyancy tanks) to rest on the bottom, close down gambling for the duration, and re-float it with buoyancy tank pump-out after.

Another alternative is the spud barge or jack-up barge concept. Anchoring a numbers of hexagons with spuds and attaching them one to another is a much better solution that multiple anchor lines. Not all of them even need to be on spuds, just enough to provide solid, stable connections for the rest of them.

I think once it’s in place, it will become such an accepted feature of the region that there will never be much call to remove it, that it will improve the environment by promoting fish habitat, providing vertical relief that shelters new spawning grounds, etc. I would bet that you’ll grow so much new reef around it that no one will be willing to force it to move because that new reef would be damaged if they did.

(Bob LLewellyn) #71

The drag on the anchoring system may become too much because of the wave action over time. So it might be that our sea homes would have to be built more like a catamaran. It would give the smooth comfort on most seas but if a big one is on the way, you would drop the building to the point where it is floating on the water and batten everything down. The wave goes over and the building is re-floated. This only puts stress on the anchoring system when a big wave is going through. It would give the village more of a boardwalk feel than the floating city feel. Floating walkways can join individual structures together so there would be no need to physically tie the barges together firmly. A barge with cat legs is the way to go for comfort and safety.

(Larry G) #72

Any anchoring system other than gravity based or tension is going to take a larger footprint than the vessel itself, which will always be problematic when trying to cluster them close together.

Either of these types of anchoring system (being straight up and down) can eliminate vertical acceleration, but has the disadvantage of not bearing side loads as well (wind and wave). The vast majority of wave force is up and down due to compression/decompression cycles, but it’s still a significant point-source of lateral load.

For the gravity-based spud barge, side loads depend largely on high high you jack up. I don’t envision an entirely hull-out-of-water scenario because there is the added difficulty of ready access to the water and increased wind loading, and a high center of gravity if you do reach the tipping moment. I would expect to jack up to the point that the legs are resting firmly on the body, with a percentage of total weight on them that can be determined stable in prevailing and extreme conditions. Since you’re talking hundreds of tons, it should be possible to calculate a decent margin of safety per side area, weight, height, and expected lateral loads that is still not even close to the full weight of the platform. One could reduce buoyancy to this point and then lock the leg height. The nice this about a hex form is it has symmetrical stability in all six points. You don’t have to worry about lateral load from one direction having more effect than the same load from another direction.


Suction anchors don’t have to be tension anchors. Often, they hold catenary lines…

(Theodore M. Amenta) #74

Landlubber’s! ---- Spark / Forexbob / JL_Frusha / Larry G ---- Can I ask you all to refocus for a moment on my specific topic. I seriously appreciate all your are teaching me by reading you postings — but: my mission is to create a sea stead that meets the TSI stated socio-economic- political objectives. I am confident they have not been able to produce a “feasible” prototype. I believe I have. The only uncertainty I have is in the naval engineering of the stability of the platforms. I expect you can help me in this. Please focus on this for me. Then go crazy about individual hexagons and single family floating seasteads ---- Please help me for a moment. My objective is to conceptualize a 300-resident seated (I do not actually agree with the politics). This new community will provide primary jobs for 150 information technology staff. This may be freelance digital nomads or co-work or venture capital start-up. — What is the cost of a platform (barge)? Do I fill the body of the platform (barge) with wage storage form a catchment system? Can I occupy the the body of the barge with humans? — I need 10% glass for sunlight (code minimum). One final thought — I have several prototypes for Polynesia, the conference starts in three days ---- Should I post? — Ted PS: This is a simple drawing of A $50 million project in Polynesia. I have done the market and financial feasibility. I have identified the hotel operator and wind energy investors ----- I GET ZERO INTEREST FROM TSI -----!!!

(Larry G) #75

Please help me for a moment. My objective is to conceptualize a 300-resident seated (I do not actually agree with the politics). This new community will provide primary jobs for 150 information technology staff. This may be freelance digital nomads or co-work or venture capital start-up. — What is the cost of a platform (barge)? Do I fill the body of the platform (barge) with wage storage form a catchment system? Can I occupy the the body of the barge with humans? — I need 10% glass for sunlight (code minimum). One final thought — I have several prototypes for Polynesia, the conference starts in three days ---- Should I post? — Ted PS: This is a simple drawing of A $50 million project in Polynesia. I have done the market and financial feasibility. I have identified the hotel operator and wind energy investors ----- I GET ZERO INTEREST FROM TSI -----!!!

  • Cost of platform barge
  • Water storage
  • Occupy with human living space
  • 10% daylighting

The barge would have to be steel with the dimensions you’re positing, or specially engineered concrete. Steel has several decades of potential use wth significant periodic dry dock maintenance. Concrete has potentially many decades to centuries with little maintenance especially if you use geoploymer concrete with basalt fiber in place of structural steel. Your local code may need a variance for this as it is not yet standard and well known. Your cost estimate of 100/sf for construction of this barge is as good as mine.

Water storage: seawtaer is about 3% heavier/denser than fresh water. So you can’t fill the majority of your platform and stay buoyant, but you don’t need to. N Americans use far too much water daily, most of it washing down a drain without ever touching human skin much less passing through a human. But health and welfare does require significant water available. You needs tens of gallons per person per day at a minimum. You don’t want to have too much of a “just in time” strategy for water production. You need to store enough to cover periods of time when the systems for producing water are under maintenance or otherwise unavailable. Redundant systems are also good, even if the capacity of each is not up to the task of full production.

Storing water low in the superstructure or lower in the hull is good for stability. Then you have to actively pump it to where it’s needed. Storing it higher allows for efficiency in pumping and then using gravity feed to assist distribution.

I recommend combinations of catchments,and seawater reclamation including active reverse osmotic systems and “dewvaporators” (low temp distillation methods.)

Combining the displacement area of the hull with human usage absolutely makes sense. Human living accommodations are mostly empty space. Might as well get double duty out of your buoyant displacement. Could be living or working space, but not storage for dense materials. For multiple reasons on this last point including work flow of materials movement.

I see no problem with your daylighting requirement. Mechanisms for securing water tight hatches and ports are well-understood.

As for posting to be in time for the conference in FP, nobody “in charge” appears to monitor this forum in real time. I think there is email and possibly phone contact info on the main website somewhere. They are probably involved in conference logistic to an extent they will not be checking in here for several days.

Are you in a position to attend the conference @tamenta ? Can @Elwar help out? Since I believe your are attending, Chad?

(Larry G) #76

In which case they still exceed the footprint of the platform.

@tamenta, you still need an anchoring system. FP is not going to be jazzed about anybody dragging massive chains and hooks across their precious, delicate coral reefs.

Tension anchoring has some kind of positive lock on the seabed, and holds the platform lower in the water than buoyancy would naturally float it. Thus, “tension anchoring”. The buoyancy and the bottom connection are in opposition and there is tension on the line between them. It can be more vertical than drag anchors and more importantly it stays put in a very specific spot, no dragging, and the precise spot can be found to have minimal Eco impact.

It also keeps your platform from vertical acceleration rolling, rocking, etc due to tides or waves. Sometime it will sit lower in the water, sometimes higher just like a natural island.

(Theodore M. Amenta) #77

Larry G — Thank you for all this and your previous input. Here are several thoughts:
1.) Cost / SF of platform barge is directly affected by draft: $100/SF for say 15 feet and $50/SF for 7.5 feet (rounding) The height of the buildings on the barge are also directed to building weight. Say 150 lbs/SF per floor. I need 4 plus to raise the platform “value” to $100/SF. or 2 plus to exceed the $50/SF cost — thus I need less displacement.
2.) Water — I agree 100% and am planning for both catchment (72" / year in Polynesia) backed up with desalinization. I will store low for ballast as the upper levels are valuable for human activity. I am designing like a ship with 85% platform coverage and most pubic space on the roof.
3.) Human occupancy is based on US building codes plus I am reading the naval conventions.
4.) 10% of floor area of sunlight ---- is US code minimum. I am well above this. I think you know I am an architect licensed in the US.
5.) Energy — There is insufficient area to be fully provided by solar. I find a bout 40%. The rest is provided by commercial scale wind turbines — of in an alternate scheme the sea stead is part of a ocean-basedd wind farm. This is located off the coast of Maine. I read that Polynesia has low wind availability — So I backing all this up with fuel-based generators.
Thank you for all your i put an effort. If there are architecture or urban design oriented questions I might answer just ask. Ted

(Theodore M. Amenta) #78

I can not be in Polynesia. I am in Miami for two weeks working on a land-based marina and hotel development. Part of my interest in testing my “prototype” in FL is that I have colleagues there. Ted

(Theodore M. Amenta) #79

I understand the need for tensioning anchoring. Thank you. I am approaching the need for a naval architect to begin the engineering of the platforms. Ted


It’s hard to envision ANY floating stationary seastead which is anchor (or moored) without a BOW.