We are working on a seastead design.

The goal is to design our seastead such that all the parts can pack into a single a High Cube 45 foot container which has:
   width 7.7 ft
   height 8.9 ft
   length 44.6 ft
   max weight:  62,000 lbs  (rated bouyancy at desired waterline is 27,500 lbs and we hope structure is enough under this that humans and their stuff can fit)

Above the water there will be a big equilateral triangle frame, 44.0 feet on a side. 
The triangle frame is also the wall of the living area and will be 7 feet high (floor to ceiling).
It will be enclosed and the whole inside the living area.
Around the whole outside of the wall, except where the dinghy is in the back, will be a 3 foot wide walkway and railing that 
is bolted on and has some diagonal supports from below bracing to the wall (so walkway is 1 food higher than bottom of the wall).
The walkway will have an aluminum grating that would let a wave pass through but you can walk on.
Also two doors on the back side,  one two feet in from left and one two feet in from the right side. 

There are 3 legs/floats/foils/wings/keels that provide the buoyancy, so it is a bit like a trimaran but with a very soft ride.
Each leg/wing will 14.5 feet long and have a NACA 0040 foil shape with 8.5 foot chord except that the last 0.5 feet of
the thinnest part will be cut short, so with foil does not come to a point at the trailing edge and fits within 8.9 feet
hight of container.  But the buoyancy is very close to that of an 8.5 foot chord foil.
Each of the 3 legs will be attached to the underside of the big triangle near one of the 3 points.
The center of the thickest part and going 1.5 feet in all directions from there will be within the area of the triangle,
but within that constraint, each leg will be as close to the point of the triangle as possible.
The legs will go down so that the lower half is in the water.
This makes for a bit of "small waterline area" similar like a small oil platform but one that can move through the water easier because of the foil shape.
It is not an extreme SWATH design as a 1 foot change in water level is about 1/7th of the total buoyancy, so still significant change.
The 3 legs will all be parallel with the blunt or "leading edge of the wing" side facing forward so it is lower drag when moving forward
than a typical cylinder on a semi-submersible platform.  
Each leg will be 50% under the water (so 0.5 * 14.5 feet) and the top 50% out of the water.
On the top half of the front of each leg, so the top half that is out of the water, will be a built in ladder.

The reason for these sizes for the triangle and legs is so they can pack into a container nicely and shipped to 
a shipyard anywhere for assembly.
Imagine the 3 legs end-to-end with thin/trailing-edge of foil up and leading edge down on the right side of the container.
So the right 3.4 feet of the container (width of legs) is used by the 3 legs.
Then the 3 frame/wall sections will be upright (so 7 feet high) next to each other along the left side of the container.  
I am not sure the width of the walls but if they were 10 inches wide then 3 widths is 30 inches and some extra is 3 feet on the left side.
There should still be lots of room in the center of the container for all the other parts.

Connecting the mid points of the walls both at floor and ceiling level will be structural beams that
make another triangle 22 feet on a side.  Then all the remaining spans will be less than 22 feet.
The rest of the floor and ceiling will be small pieces that are bolted in.

On top of the roof there will be solar all over.  With batteries and electric thrusters as the main propulsion system.

There will be 6 RIM drive thrusters of 1.5 foot diameter, one on each side of the 3 legs/wings about 2 feet up from the bottom.
These RIM drives will be all be fixed orientation to provide forward thrust.  It will use differential thrust to turn.
For slow movements in tight areas like harbors it can reverse thrust on one side and forward on the other to turn in place.

There will be a conduit/pipe welded to the back of the trailing edge to take electrical wires down to the thrusters.
There will not be any "through hulls" in the legs.  The legs will also have multiple
airtight compartments each for safety.


Behind the back near the center will be two supports going out and 2 ropes going down to a dinghy.
The dinghy is a 14 foot RIB boat (deflated for shipping) with an electric Yamaha HARMO outboard.  It is sideways against the center of the backside of the living area.
When the seastead is moving forward the dingy is shielded from the wind by the living area.

On the lower part of each leg will be several bolt on heave plates.  These will help dampen the response to waves.

About 25% of the displacement will be for LiPo4 batteries which will be put low in the 3 legs.
Each leg will have its own charge controller and inverter so there is triple redundant power on the seastead.
Also, the thrusters for a leg will get power from that leg's inverter or batteries.  So
the 3 pairs of thrusters will have independent failure modes as far as power.

When the seastead is going to be staying in one place for awhile, we can put down 3 helical mooring screws and give the seastead tension legs 
so it becomes nearly stationary when parked.  Near each corner there will be a pair of helical mooring screws with a motor unit between them.
We only plan to do this in the Caribbean where tides are very small and in protected places where the saves are small,
so pulling down 3 feet will be sufficient to never go slack.


Two seasteads will be able to connect together with a walkway, one behind the other, so that while underway 
people can move between seasteads, enabling a real community.  The two computers for the two seastead will both work thrusters
to minimize the movement of the walkway, particularly when warned that someone will be on it.




Here I want you to look at other backup ways of moving the seastead
if there is a problem with the main method.   

1) We are using differential thrust so we need at least 1 working thruster on each side for normal operation.
So we will have some redundancy in the primary propulsion since we will have 2 thursters on each side.  


2)
I would like to look at the efficiency of kedging a seastead with sea anchors.
Imagine we have 2 sea anchors attached to 2 winches on the seastead with long ropes
and another long rope that goes through a pulley on the dingy and to the center of each sea anchor.
This is not for storm conditions, just nice conditions.
The seastead will pull on one parachute and so when the dingy goes forward it will not be
able to pull on that one it will pull on the other sea anchor.  After it is far ahead
and the other sea anchor is getting close to the seastead the seastead will switch to pulling
on the other sea anchor and let the line out on the first one.
So it is kedging but with sea anchors instead of bottom anchors.

It seems that a large sea anchor will pull on a huge mass of water, so the water will
not move very much, so it seems it could be reasonably efficient. 

For simplicity for now, lets ignore the energy of the dingy and try to estimate
how fast the seastead could move if it was always using 2000 watts pulling on one
sea anchor at a time (well during switch it will start pulling on new sea anchor and only
after it has inflated and pulling back will it stop pulling on the previous one, so there
can be a tiny overlap but we can ignore that for now).  
Lets say 10 meter diameter sea anchors (though let me know
if you think this is a good size).  What would such sea anchors cost and weigh?


j)
Next please look at how fast kedging with regular anchors in shallow water would be with 2000 watts.


4)
Next imagine we have a small boat (big 14 ft dingy) with the seastead that we use to go to shore
after parking the seastead in deep water with one Yamaha HARMO electric motor (RIM drive).
In an emergency we will have two other HARMO drives we can also put on the dingy so it has
some ability to pull the seastead.   Each motor has 227 lbs thrust so 3 together is 681 lbs thrust.
This can pull the seastead somewhat.   We can run a power cord from one of the seastead battery
banks down to the dingy so it has plenty of power.

5) 
There is no dagger-board or rudder on the seastead so under kite power it goes the direction the kite is pulling.
We will have a 2 string kite where really a single string comes down one side, goes through a couple pullies,
and goes up to the other side of the kite.  This is so a human (or maybe robot/computer)
can control the kites and fly figure 8 motion in the sky at a good angle to optimize the amount of pull.   
Imagine we have a stack of 20 kites each 6 feet wide by 2 feet front-back.  
If we are in the Caribbean and have 20 mph wind what sort of speed can we get for these angles:
    1) directly downwind
    2) 30 degrees off of downwind

If this is more than 2 MPH, how many of these 6 feet wide kites would be enough to go 2 MPH?

6) 
If a friend with a second seastead is nearby they could tow the seastead with problems, though slowly.
In another location we look at having a rope bridge to go between 2 seasteads and the one
behind giving power to the one in front so it can have more power for thrusters.  If we are
able to use power from two sets of solar panels and batteries then it can run the thrusters
at a higher power level and go faster.

7) 
If only one thruster is working (or only 2 on the same side) it should be possible to keep the body at some angle relative to the
wind such that the seastead moves downwind, and off to the side some if desired, to move in a 
useful direction (closer to a rescue ship or port).