Who's new
Who's online
There are currently 1 user and 19 guests online.
Online users
Recent user registrations
Registered Users
Low Cost Seastead
Wed, 08/20/2008 - 02:18 — Wayne Gramlich
I just thought I would share my latest thoughts on low cost seasteads . As usual, the raw material is in the wiki so people can fix obvious problems. General discussion, seems to work better on a dedicated forum thread -- hence this post.
It should be no surprise to anybody that I am thinking in terms of a smallish truss-spar design. Read the wiki page for more detail. If anybody who is skilled with 3D modelers wants to try drawing the thing, I would be deeply indebted to you.
I'm guessing the main
I'm guessing the main purpose of these low cost seasteads would be a more direct commercially operated platform for recreational activities, fishing, diving, boating ect. Rather than a long term seastead solution.
I'm no engineer but the theory looks solid. How many people could each one support? And at what length of endurance.
Reason
The purpose of a low cost seastead is to expand the number of people who want to give it a try.
I like it. This should make
I like it. This should make for a lighter structure overall - lighter ballast neccessary, less structure needed underwater - thus making it cheaper. It will probably be more prone to bobbing up and down than a full size (and overall denser) spar, but should be ok with respect to rotational movements. I´m not entirely clear how the wires will function though, and having the ballast function as a air chamber, although clever, and probably useful, could present some problems with complexity and/or rust inspections. I guess you could build a really simple version with the truss made of just welded L-profile steel (like a power pylon) and a stack of square (or whatever shapes are available on the market, this shouldn´t matter all that much) steel plates as the ballast though.
Another benefit of this design is that you get rid of (and don´t have to pay for) all that internal space far below the water surface (in a full length spar) where noone would like to live anyway.
This should also be easier to tow and move, with the hollow truss producing less drag than a spar.
Cable Truss
It is really hard to describe the cable truss...
Please do the following. Take two equilateral triangles. Position one triangle above the other, but rotate it by 60 degrees. Now connect 6 rigid struts between triangle vertices. Now place a few more of equilateral triangles above the ones you have, rotating each equilateral triangle by 60 degrees.
For the cable truss, the equilateral triangles are mounted on the vertical pipe. The rigid trusses above are replaced by 6 stainless steel cables.
I have tried to draw this on a piece of paper and it completely exceeds my ability to draw it.
I saw your sketchup drawing
I saw your sketchup drawing now. That is some pretty funky design. Why do you feel this is better than a regular "truss-like" truss (i.e. like a power line tower)? I am asking because this seems like the most obvious, simplest and cheapest choice to me.
Truss Choice
My cable truss may be too cute. It may be the case that a more normal truss structure is less expensive. Suffice to say, minimizing truss cost is paramount. By minimizing cost, I include both material and labor cost.
Its not really a pivotal
Its not really a pivotal feature of the concept. The space between the hull and the ballast needs to be bridged in a rigid fashion. Hard to tell which way is best without narrowing down on the static and dynamic loads this thing is going to have to deal with.
Seconded...
I like it, too. This will add an entirely new level of people willing to join this movement. A 1500 sq. ft. dwelling that can survive a hurricane is great all by itself. Apart from new governments, I can see something like this being implimented just off shore of major population centers. The benefits of everything. I am really digging this design.
Deep Draft
This structure will have a deep draft due to the truss and ballast/damper. It may not be possible to bring these all too close to shore.
I can imagine a structure where the truss can be raised an lowered, but the complexity of such a design gives me the creeps.
It needn´t be that deep. If
It needn´t be that deep. If the cylinder is half submerged and we assume equal density throughout it should stay upright with the lightest of ballasts, and only a small leverage arm. If the roof is 3m above the sea (the top floor in the air and the bottom floor submerged, total 6m/20feet cylinder height ) I´m sure you could get away with like three times that below the sea as leverage. So, 9m(27feet) draft.
edit: Now I´m somewhat unsure whether my buoyancy logic above holds true... about the average density of the cylinder. It must be less than water anyway, for a number of reasons (like not sinking...).
A buoyancy program that lets you design simple shapes and experiment with CG, density etc would be very useful for these excercises...
Cylinder is mostly air
Just like a boat, the interior is mostly filled with air. Even though concrete is denser than water, the exterior shell is not heavy compared to the amount of water being displaced.
A spread sheet would really help out here.
This seems indeed like the
This seems indeed like the most affordable design imaginable, and it seems like it would work well also.
This design is the one most similar to a ship, so lit lends itself well to comparisons with it. The two things that sets it apart from a ship are extra stabilization and a hull aimed at low cost construction, both at a sacrifice of manoevrability and speed. An excellent tradeoff given the different design requirements compared to a ship.
I could do some solidworks modelling, to give a feel of the dimensions and some possible implementations of this concept, but as i explained eariler, no pretty pictures unfortunately. If you are interested, let me know.
Picture
I was able to coax some software into drawing a rough picture of the basic idea. The image is attached to the main wiki page.
If people have better drawing skills than me, I will not be upset if they draw a better picture.
Hey dont go overboard with
Hey dont go overboard with the enthusiasm :)
I made a simple model, ill see if i can add it to the wiki (never tried that before)
Ok, i just added two pictures and a paragraph to the wiki. Feel free to merge it into the rest if you see fit.
Looks Great
Your cable stabilization is simpler that what I propose.
It is probably better to keep the windows above sea level.
Have you ever been to a zoo
Have you ever been to a zoo where they have these underwater tunnels? Its essentially the same situation. Plexiglass is tough stuff, appearently its deemed safe in such applications.
If you do not know what i am talking about: the first result of googling 'underwater tunnel'
http://www.planetware.com/i/photo/valencia-e1272.jpg
Risk/Benefit Ratio
Most boats do not put windows below the waterline unless they have a good reason to do so. The exception is "glass bottom" boats.
Risk of putting a window below the water line is that it will spring a leak. There is not much to see underwater in the middle of the ocean. It is clearly technologically possible, but Is the risk/cost with the benefit?
I still like your basic picture, it is better than mine.
Well, there might not be
Well, there might not be much to see, but i think you can still get a fair amount of light at that depth. A window a few meters above the waterlevel will need to hold up to the same standards, because its going to be effectively under water quite a lot of the time. That line of argument quickly leads to no windows at all, and although personally i dont really care, no natural light is generally frowned upon.
As for leaks: if you mean catastrophic leaks, i think the plexiglass can be made such that the concrete would fail before the glass would. Minor leaks would not be a big problem, and should be very preventable.
Portholes
Here is some related reading.
http://en.wikipedia.org/wiki/Porthole
http://en.wikipedia.org/wiki/Saale_disaster
I hade the idea earlier to have the windows unable to open to decrease risks with flooding. Perhaps not a good idea after all.
I was thinking of steel
I was thinking of steel frames cast into the concrete, with a thick slab of plexiglass clamped and bolted to these steel frames. Thats not going to leak short of a torpedo.
As a result of this disaster it was legislated that portholes had to be big enough for a person of reasonable size to escape.
There are many effective ways to lessen the risk of fire. This doesnt seem like one of them. Either way, a closed window isnt any harder to climb through than no window at all.
Well, I´m not going to set
Well, I´m not going to set foot on any seasteads that have no emergency exits. Fire prevention is all well and good, but you should expect there to be fires anyway, and try to reduce the potential damages with that in mind (within reason). I am quite sure the people who built the Saale thought they had eliminated any chances of a fire.
Besides, if there are laws about the openability and size of portholes we might have to comply with that anyway to stay out of trouble with the law. For the first few seasteads anyway.
I disagree with that for two
I disagree with that for two reasons.
First of all, if you expect seasteading to be a walk in the park, i think you will end up desillusioned. Things like this seem like the smaller of the risks that you will have to take as a pioneer.
Secondly, its simply not rational. A well-built seastead, with modern techniques and materials is probably orders of magnitude safer than your average wooden construction, which many mostly older houses have. Extra fire escapes or not.
First of all, if you expect
First of all, if you expect seasteading to be a walk in the park, i think you will end up desillusioned
What gave you that impression? I just stated that I expect to have to escape a fire through a porthole into the sea. Hardly a walk in the park IMHO.
Granted, your alternative of being burned to a crisp is even less of a walk in the park...
I don´t know if the Saale was made of wood or steel but that doesn´t really matter. All the crap you have inside (furniture, equipment etc) is what burns and produces smoke in a fire.
The house im in right now
The house im in right now has no sprinklers, nor alarm system, is full of wood, three high, with only one narrow staircase going down. A fairly typical situation.
Im not saying we should disregard safety, but we should keep the big picture in mind. I doubt making holes in your hull adds more safety than it takes away.
There is a lot of things that can be done, like keeping fuel storage outside the main hull, and a well-sprinkeled ladder in the elevator shaft.
Three floors without a fire
Three floors without a fire escape seems rather unusual to me. Personally I´m no big fan of mandatory building codes but that doesn´t mean you have to disregard all safety. Are you sure your building complies with the relevant regulations, if any? I´m in Sweden by the way, perhaps it´s just our regulations that are extra draconian...
Well, if portholes on ships in general are openable, and the regulations say they should be, that would indicate that the consensus is that this is the safer way to go, on balance.
Even if you flood an entire floor through an open window that shouldn´t spell disaster. There should be bulkheads and waterproof doors between floors, right? And before it comes to this you should have some time to close the port. You could have alarms that go off when there is water on the floor, you could have centrally mounted indicators for open ports, you could have the portholes only openable as an emergency exit, with an alarm that goes off throughout the steastead when opened. Etc.
And in general, having them openable gives you more options. Yes, in some respects it increases the risks. But in other it decreases them. All things equal I´d rather go with the way that gives me more choices when the shit hits the fan, because it will, eventually.
Trade-offs
My attitude is that if we can not design something that is better than a boat for our application, then people will simply buy boats instead. (I know that is what I would do!) The goal is to lower cost with improved comfort and safety with respect to boats.)
Another key concept behind this design is that is meant to be mass produced. The concrete forms for the living structure could be used over and over again. A jig could for the truss/ballast/damper could be easily assembled to make truss/ballast/damper construction really easy. I can imagine a factory that grinds these babies out at a rate of 2 or 3 per week.
_
Nice.
I corrected a mistake i
I corrected a mistake i made:: given the dimensions as they are now, each floor would have 92, not 46 square meters of floor area. Quite a difference.
This "heave plate" thing
This "heave plate" thing could put very large stresses on the truss and bottom of the cylinder. It will effectively be anchored in the water, by means of large water drag. Any waves lifting the cylinder will have to fight against this anchor. Without heave plate the waves will just be accelerating the counterweight which shouldn´t be that much of an increase in stress compared to the whole structure being at rest.
I am not saying it will not work as advertised. It certainly will decrease heaving. But the increase in truss dimensions required to take the increased stresses might be too costly to make it worthwhile.
It seems to me like a heave plate is sort of fighting the ocean, while a truss and counterweight that just floats with the waves is a more "go with the flow" approach, and as such, more efficient.
I could be wrong though, just throwing these thoughts out there.
You could of course also put vertical plates to deal with lateral/rotational movements. Which may or may not suffer from the above mentioned problems.
You are right, a heave plate
You are right, a heave plate could potentially cause quite big dynamic loads on the truss. However big, i think they should basically be on the same order of magnitude as the static loads.
The dynamic loads are due to a fluctuation in flotation. The static loads are pretty much proportional to flotation, since the ballast should be on the same order of magnitude as the weight of the structure itself to have any effect.
Its something to keep in mind, but not a dealbreaker.
What i am worried about is horizontal motion. Waves create quite some horizontal displacement, and i do not see an easy way to counteract that effect.
Then again, horizontal movement of water merely has a drag effect, not a flotation effect. drag << flotation. Probably the structure is simply too heavy to be affected much by fluctuating horizontal forces.
Another potential drawback
Another potential drawback with a heave plate on a buoy like this is that it might increase sideways movements when the cylinder rides up on a wave slope. And it could possibly push the cylinder entirely out of the water if things go really bad.
At least when considering small seasteads. These are small enough to disappear completely below a decent wave and will probably always have a wild ride in a storm. The goal here is survival, not necessarily comfort.
But it´s clear we need to model this in a tank to find out for sure.
Marine Engineering
We need some marine engineering here. We are pretty much at the limit of what I can figure out.
Heave plates are used in the offshore industry, so the real issue is how big and what are the trade-offs. Other than asking a marine engineer or building a model, I do not know how to answer the question.