We are working on a seastead design.

Above the water there will be a big triangle frame.  The
left and right sides will be 70 feet long and the back part of the triangle will be 35 feet wide.
The point opposite the 35 ft side is the front.
The triangle frame will be a truss structure that is 7 feet high (floor to ceiling).
It will be enclosed and the whole inside the living area.  Lots of glass to see out.

There are 3 legs/floats/foils/wings that provide the buoyancy, so it is a bit like a trimaran but with a very soft ride.
Each leg/wing will 19 feet long and have a NACA 0030 foil shape with 10 foot chord and 3 foot width.
Each of the 3 legs will be attached to the underside of the big triangle near one of the 3 points (but the total top of the
leg will be inside the triangle) and going down so that the lower half is in the water.
This makes for a "small waterline area" similar like a small oil platform but one that can move through the water easier because of the foil shape.
The 3 legs will all be parallel with the blunt or "leading edge of the wing" side facing forward so it is low drag for the seastead to move forward.
Each leg will be 50% under the water (so 0.5 * 19 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.

There will be 6 RIM drive thrusters of 1.5 foot diameter, one on each side of the 3 legs/wings about 3 feet up from the bottom.
These RIM drives will have the flat sides toward the front and back of the seastead.

On top of the roof there will be solar all over.

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 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.
Also behind the back on the left and right of the dinghy will be a deck that is 5 feet wide extending beyond the back of the triangle.

There are 3 stabilizers that look like a little airplanes, one attached near the back of each main seastead leg.  
The little airplane has a 12 foot wing-span, 1.5 foot chord, the body 6 feet long, and the elevator has a 2 foot wing-span and 6 inch chord. 
A small actuator makes the elevator angle up or down so it can adjust the angle of 
attack of the main wing of this stabilizer without needing a large actuator.
This is really the "servo tab" idea.
While the thick part of the leg is 3 feet wide the back where the airplane will attach is very thin.  And to get the airplane's
center of lift to balance on the pivot a notch into the front/center of the wing only has to go about 25% of the chord of the wing.

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.

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.   




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).