We are working on a seastead design that will have a 40 by 16 foot living area above the water.
There will be 4 foot diameter legs/floats/columns that are about 24 feet long going out from 
from the 4 corners of living area and down into the water at 45 degrees, with half of
each column under water.   The legs/floats/columns will probably be made from 1/4 inch
thick duplex stainless steel on the sides and 1/2 inch thick on the dished ends.
They will have some modest pressure like 10 psi inside.

The bottoms of the floats will make a rectangle about 50 feet wide and 74 long.
From the bottom of each leg there will be 2 cables going to the adjacent corners.
The boyancy force is lifting up and the leg pushing against the platform leaves an outward
force that the 2 cables pulling in counter, so the leg ends up staying in place.
There will also be a cable making a rectangle between the bottoms of all the legs so we have some
redundancy in case one cable breaks.
The seastead is about 36,000 lbs I think but this is NOT a normal boat hull shape,
it is more like a tiny oil platform as far as drag.

We expect to use 4 low speed submersible mixers with 2.5 meter diameter propellers as 
thrusters, one on each leg/float.  There will be lots of solar and battery.
This should move at around 0.5 to 1 MPH plus any help from careful use of eddies and currents.




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).