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 wide columns that are about 20 feet long going out from 
from the 4 corners of living area and down into the water at 45 degrees, which half of
each column under water.   The bottoms of the floats will make a rectangle about 44 feet wide and 68 long.
From the bottom of each column there will be 
2 cables going to the adjacent corners to hold it in place.
There will also be a cable making a rectangle between the bottoms of all the floats so we have some
redundancy in case one cable breaks.
The seastead is about 30,000 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 2.5 meter diameter propellers on two low speed submersible mixers and solar power to move
at around 1 MPH plus any help from using eddies.


When a thruster pushes on water the thrust is proportional to mass of water moved times
the speed the water is given.  It is Newton's equal and opposite reaction for 
the momentum given to the water.  The energy is 1/2 times the mass of water times
the velocity squared.  So looking at static thrust or bollard thrust the
energy needed goes up with the square of the velocity but the thrust just
goes up with the velocity.   So the best static thrust per energy is with
lots of water moving very slowly.

So the low speed submersible mixers with 2.5 meter props turning at low RPM are 
a reasonable idea.

I want to look at another possibility though.

Imagine between the bottom of the back 2 floats we have two cables say 1.5 meters apart.
Then on this we have a wing attached to both cables with maybe 4 wheels or pullies so
it is able to go back and forth along the 2 cables.  The wing will flip back and
forth so that as it moves across it pushes the seastead forward either way.
This can let us push on a lot of different water so it could be very efficient.
If we could get the wheels inside the wing that could help efficiency.
If it goes back and forth staying over on the right half, it could turn the
seastead left, and if it pushed more on the left side it could turn the seastead right.
So one of these could be enough to both push and steer the seastead.
It seems like it might be a good way to propel the seastead.  What do you think?