The design goals are discussed at http://seastead.ai/ai/seastead.goals.html
DESIGN IDEA
We want some ability to move but maybe like
0.5 to 1 MPH. We really plan to look at which way ocean gyres are and make a route to
take advantage of all the currents and wind. We will have very large propellers.
I think the 3,000 watt 2500 mm submersible mixers from China that are used
for sewage mixing produce and produces 2090 newton thrust could work.
These are sometimes called "banana blade mixers".
I think there are salt water rated versions in the $5,000 to $8,000 price range.
For redundancy, we will probably have one on each leg (so 4 total). Also a spare in storage.
If we have at least one working propeller on port and one working one on starboard we should have reasonable control.
With 4 total we will have close to 2000 lbs thrust at 12 kw.
The propellers will be far off to the sides so differential thrusting should work well.
No need for a rudder.
The living area or "body" will be out of the water. For shipping the corrugated culvert
idea seems good, just bolting together pieces. The "structural aluminum plate" in the
"box culvert" shape seems good. This has a corrugated flat bottom and a corrugated side/top section.
It all bolts together.
Lets do 40 feet long and like 16 feet wide and 9 feet high in the middle (sides will more like 6 feet).
Looking at 2 choices:
1) 2 mm corrugated Duplex Stainless Steel (e.g. 2205 ).
2) 3 mm corrugated marine aluminum
The choice will probably depend on the metal used for the floats/legs.
The corrugated pieces will stack for shipping and be assembled on site (as is common for large corrugated culverts).
The body will have internal support frame that makes a rectangle in the bottom edges.
This is to make 4 "hard points" corners where the legs will attach.
Part of the reason the body is 40 feet long is so that the beams can be single pieces.
The front and back of the body will have lots of glass with glass doors.
The 4 floats/legs will be the buoyancy.
I am looking at 2 choices for these:
1) Duplex Stainless Steel (e.g. 2205) 1/4 inch thick for sides and 1/2 inch for the dished ends
2) Marine aluminum 1/2 inch thick for the sides and 1 inch thick for the dished ends.
Please discuss the weight, cost, and life expectancy of these 2 choices.
Each leg will 24 feet long and halfway in the water, so the water displaced is from 4 cylinders of
3.9 foot diameter and 12 foot each. What is the total displacement?
There will be 4 legs that go down and out like 45 degrees from the 4 corners of the living area.
I am thinking of a modest air pressure inside the floats to make them structurally stronger, maybe 10 psi.
We can also monitor the air pressure so we would get early detection of any leak.
There will also be say 8 air bags inside each leg. These will about fill the leg
before we add the 10 psi but be smaller after that. If pressure is lost they will expand
back so that water can not fill too much of the leg. There will be a bolt down hatch
at the top end of the leg with rubber seals that can be removed to inspect or change the air bags,
after pressure is equalized.
There will be stairs with rails going down the top of each leg. There will also be a
couple seats on each leg so people can sit down and fish.
A saefty ring around the leg like a foot above average water level so someone could grab onto
that if they were in the water.
This is a tensegrity structure, the joints between legs and body are flexible though we don't really expect movement.
The leg itself is a compression member.
Each of the legs will have two cables, one to each of the adjacent corner hard points on the rectangle frame.
The leg will be heading away from the corner it is at and down into the water at 45 degrees.
The buoyancy force will want to lift the leg up but the two cables will hold it down.
We can have an extra backup cable making a loop around the bottom of all the legs. This gives us some redudancy
where if one section of cable someplace breaks we are still ok. This will be jacketed (covered) Dyneema.
If we use duplex stainless for the floats then duplex stainless for the cables makes sense.
If we use marine aluminum them perhaps jacketed Dyneema for the cables is good.
We want lots of extra strength margin on the cables.
What do you recommend?
How often should they be inspected, cleaned, replaced?
The legs and body will sort of have a ball and socket connection with some rubber (like car tire rubber)
in between. It is only a compression joint, no torque. The rubber also helps keep electrical isolation.
The rubber probably helps isolate some wave sound as well.
The 3.9 foot diameter is so we can get 4 into a 40 foot container. We do
not want to increase the diameter or length of the legs. We could increase the length if there are weight problems.
That will be extra cost and drag so we are hoping not to need to.
The 3.9 foot diameter legs make for a small waterline area. Waves will
have little impact so the motion will be gentle on the humans.
The legs in the water will make a lot of drag (we are clearly optimizing for ride comfort
and not speed).
If the top and 3 sides of the body (left, right, back) are covered with solar. In normal weather the solar on
the sides will swing out (about 6 feet out each) so it is level with the roof and be brased to stay there.
For storms these will close down to reduce windage.
Please estimate the total "installed watts".
Note that there will be different strings of solar panels going the length of the body at each angle,
so that all the panels in one string have the same angle to the sun.
Not all will be in the sun at once, estimate the total watt-hours we might per day.
If we wanted to be able to store 2 days worth of energy in LiFePO4 batteries, how heavy
would the batteries be?
If we used a days worth of stored energy evenly over a 24 hour period how many watts would we have?
We will spread the batteries and any tanks or heavy things in the 4 corners since
putting the weight to the corners increases rotational inertia and so reduces motion from waves.
We will have 4 seperate solar/charge-controller/battery/inverter systems so a problem with one
does not leave seastead without power. Can have connections between them with breakers to issolate in case of trouble.
Imagine we are in high winds and turn the seastead to point into the wind. So the
drag is the end of a 20 foot diameter cylinder. What sort of
drag would we have for 30, 40, 50 MPH winds and how many watts would it take for our
propellers to hold the seastead stationary?
For a normal day in the Caribbean estimate the average watts power draw of all electrical components.
How much percent extra solar power do we have?
The seastead will be pushing the leg through the water and the water
and waves can push sideways on the leg. If the two ends of the leg are held, what sort of
sideways water speed would make pressure enough to buckle the leg?
Also discuss if you think it is better to use one type of metal for the
legs and a different for the body or keep all the same.
Imagine we get a company in China to make the body and legs, and probably get other parts from there as well.
Please estimate weight and cost for each of these:
1) legs
2) body
3) tensegrity cables
4) motors and motor controllers
5) propellers
6) solar panels
7) solar charge controllers
8) batteries
9) inverters
10) 2 water makers and water storage
11) air conditioning (AC) - maybe 4 units for 4 rooms but only using 1 or 2 at a time
12) insulation
13) flooring, cabinets, kitchen stuff, furniture, bathrooms, bedroom
14) waste tanks
15) glass and glass doors at ends
16) refrigerator
17) biofouling weight gain in first year
18) safety equipment
19) dingy
20) 2 sea anchors
21) kite for propulsion. Can use as backup, fun, or extra speed - perhaps stack 20 kites of 6 foot each
22) 8 air bags in each leg so 32 total for extra safety in case of leak in leg
23) 2 Starlink - need a backup
24) anything else to finish it out
We want enough foam insulation under the roof that even if we lost one of the legs the body would still
have part out off the water so the people have a good chance to survive either by staying with the
seastead or moving to a life raft. Need to be able to exit from either end.
Also totals for weight and cost.
Try to estimate how much the body would tip in terms of feet higher or lower between front
and back of body section if a typical Caribbean wave of the following heights were to pass:
1) 3 feet
2) 5 feet
3) 7 feet
If the Seastead was sideways to the wind at what windspeed would it capsize?
With 4 legs is there a risk that the wave motion causes the cables for one leg
to go slack and then suddenly get tight and snap? I think this is "impulsive loading". Try to estimate
what sort of waves would make this start, how much shock absorbing the cables can do,
and at what level the cables might break.
If we have the Nylon at the top it can stretch some and we can see how much it is stretching and figure out the load.
I also think of doing 3 legs to reduce the chances that one goes slack, but for now I
think we will see if it is manageable with 4 legs.
What do you think?
The anchors are a bit tricky because of all the cables. The current plan is to have the
2 anchor chains/ropes suspened below the two front floats and the anchor will stay at the bottom of the
float when not in use. This is a bit extra drag but at 1 MPH it won't matter much.
The corrosion on the anchor will be more but I am thinking we probably want duplex on the
anchor and chain too so corrosion should not be too much of an issue.
Also thinking of using 2 sea anchors to do kedging in deep water. These might have to attach
from the floats near the waterline. I have a different prompt where we look at kedging
speed so ignore that here.
What length catamaran would have comparable inside square footage to this seastead?
About how many times the cost would that catamaran be compared to this seastead?
Would you agree that this seastead will pitch and roll less in 7 foot waves than a 100 foot catamaran?
If we rented at $1,000 per day how many weeks of rentals would it take to pay for the seastead?
If we are in a storm (not hurricane) in the Caribbean or Mediterranean and we put out the sea anchor tell
me what are the bad cases to worry about. Like how fast will it drift down wind? How high could the
waves get? Would you expect this seastead to be ok in waves that high? How long could the storm last?
How far could we drift during the storm? With current weather forecasting ability is it safe to assume
we would always have enough warning time to either get out of the way or at least we could position the
seastead to have enough open ocean downwind for drifting before the storm got to the seastead?
I would love to test on in a storm without anyone on-board. Maybe even test in a hurricane to see
how bad things could really get before it was destroyed.
In St Marten the big lagoon will have a lot of yachts during a hurricane. Some will come lose
and these will then bang into others destroying them as well. I suspect that if a fiberglass
boat hits against this seastead the seastead may not get damaged much. What do you think?
Probably we have a small crane on the back to lift up the dingy or submersible mixers. So we could replace
a thruster if it breaks.
FEEDBACK
Also feel free to give any general feedback on:
1) viability of current concept as a profitable business product
2) how concept might be improved
3) how big a market niche this first product could become
4) Conventional wisdom among many boaters is that a fast boat that can keep away from storms is the safest way.
This seastead is not fast. What limits or problems might this cause in practice?
5) Are there single points of failure that you think need to be further addressed or is what we have good?
Summary section.
For a summary at the end please list:
1) estimated total cost for first unit and cost each if we ordered 20
2) average solar produced, average solar used not counting propulsion, average power left for propulsion
4) lbs extra buoyancy for customers and their personal stuff