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.   





It seems it might be good to build a prototype seastead that was half size, still with Marine Aluminum.
At half size it is like 1/8th the mass, so it would be too small to live on
but plenty big enough for a few people to ride around on.  It would let us
work out some software and smaller stabilizers.

It would only be ok on days when the waves were below some level, but probably
plenty of days for that.  In particular the west/downwind side of Anguilla 
has a reef protecting from the North and the main island protecting from the
south and east, so there is a lot of sheltered water for testing a smaller size in.


This will not need to cross ocean, just go out for a few hours of fun.
We will probably make it go the same sort of 5 or 6 knots we plan for the full sized (so not really Froude scaling).
So if the stabilizer foil has 1/4th the area and goes at the same speed as full size
but with 1/8th the vessel weight, it sort of has 2 times the power relative to total weight
and so will work better for stabilizing.  This is nice since a smaller boat
sort of needs more help in the waves.   

If we have 50 kwh of batteries, how far do you think this half size version could go at 4 or 5 knots?

Making it 1/8th the weight can be a little tricky because you can't make the aluminum skin 1/8th 
the thickness.   If it is a day sailor we can just have some seats and a net like
on catamarans, so we probably can keep the weight low.  
We don't need fridge, watermaker,  etc.

I think 2 of the Yamaha HARMO RIM drives could work for this.  They are about $5,000 each.
It seems you can remove the actual RIM drive from the normal outboard mount and mount them
down on the legs (Yamaha has shown alternative mounts like this at boat shows).

Imagine a company in China makes the 3 legs, 3 sides of the triangle, frame for solar,
stabilizers, etc., which would all fit
in a 40 foot container, and we just bolt it together in Anguilla (no welding) and install the batteries, RIM drives,
stabilizers, etc.   We can use a much smaller and lighter inflatable dinghy, mabye 7 feet.
There may be suitable marine aluminum truss parts as off the shelf items.  Do you know of any?
What do you think a half size version would cost to build? (assume me and my boys assemble it for free, and 
we really do have a crane to put it in the water ourselves)

Please try to estimate the weight for the legs,
triangle truss, seats, batteries, and net.  How much extra buoyancy is there for people and cargo?

If the prototype waterline is a bit above 50% of the leg/float it is probably still ok.
Also, we can really use the stabilizer as a lifting foil
to carry some of the weight when moving.  It kind of seems like it might be a reasonable and fun day sailor.