What would it take to build a semi-submersible seastead community?
One promising seastead design based in existing technology is the semi-submersible – a very stable floating platform, most often used in the offshore drilling industry. Our engineering team, led by George Petrie, set out to determine the feasibility of this design for an early seastead platform in terms of costs and logistics, while factoring in the necessary amenities to sustain a small residential and commercial community. The study is part of our Floating City Project, but is not the only design under consideration. We are also partnering with Dutch aquatic urban design firm, DeltaSync, to engineer a novel architectural seastead design. We will release the design in the Fall of 2013.
The top-side residential and commercial space was designed by naval architect Lina Suarez, whose full report can be viewed here.
Methodology
In order to produce realistic estimates for the seastead – the semi-submersible hull and deck structure – our director of engineering George Petrie rendered a hull design based on industry standards, and submitted it for bidding to several shipyards. As of May 2013, only one shipyard – located in Texas – returned a bid. While the figure quoted represents the single largest expense for a semi-submersible seastead, there were numerous other costs which needed to be estimated based on educated estimates, previous research, and quotes from maritime professionals in our network. Estimates for the structure and basic systems were based on existing technologies, at current market rates and employing standard installation protocols used in offshore industries.
Simultaneously, Petrie worked with a Naval Architecture intern, Lina Suarez, to produce a novel top-side design for residential and commercial units, which can be rearranged to fit the Institute’s vision of a modular seastead. In turn, the cost of these units was estimated to produce full plans and cost figures for a complete seasteading community. The specifications, estimates and visuals for the platform are one part of our Floating City Project, and are available to anyone looking to actualize this vision through collaboration with the Institute, potential customers, and outside sources of financing.
Results
General Specifications
| Number of units | 180 | Residential square footage | 105,600 | |
| Average residents per unit | 2 | Commercial square footage | 125,200 | |
| Total population | 360 | Common Area: | ||
| Number of decks | 5 | • Roof top area (sq. ft.) | 22,040 | |
| Number of cranes | 2 | • Floating pier (sq. ft.) | 17,500 |
Overall CapEx Estimate
| Component | Cost | Component | Cost | |
| Hull and Deck Structure | $115,492,000 | Corner towers, common areas | $1,250,000 | |
| Transport to Caribbean site | $2,000,000 | Roof top areas | $2,750,000 | |
| Anchor Handling Tugs | $560,000 | Helideck | $1,000,000 | |
| Fuel for Anchor Handling Tugs | $140,000 | Floating Pier | $2,625,000 | |
| Revolving Cranes | $1,500,000 | |||
| Mooring System[1] | $15,000,000 | |||
| Fuel System | $1,000,000 | Sub-Total | $186,597,000 | |
| Ballast System | $1,000,000 | |||
| Fresh Water System | $1,000,000 | Engineering | ||
| Waste Treatment System | $1,000,000 | Pre-FEED | $559,791 | |
| Navigation & Communication | $1,000,000 | FEED | $1,865,970 | |
| Lifeboats & Lifesaving Equipment | $1,000,000 | Construction Support | $5,597,910 | |
| Safety & Firefighting Systems[2] | $1,000,000 | Project Management | $7,463,880 | |
| HVAC System | $1,000,000 | Contingency | $18,659,700 | |
| Residential modules[3] | $17,280,000 | Supply/Transport Boat (optional)[4] | $5,000,000 | |
| Deckhouse structure | $15,000,000 | |||
| Gensets (two @ 1000-kW each) | $1,000,000 | Total | $225,744,251 | |
| Cooling System (FW & SW) | $1,000,000 | |||
| Batteries | $1,000,000 | |||
| Power Distribution and Control | $1,000,000 | Per Sq. Ft. of interior space | $978 |
[1] From Parametric Study p. 28
[2] Eight (8) 120-person enclosed lifeboats, $125,000 each, from Alibaba.com
[3] 180 duplex modules at $96,000 each
[4] Capacity ~ 20 people, speed ~ 30 knots, docked at platform
Overall OpEx Estimate
| Item | Capital Cost | Annual % Maintenance Cost | Annual $ Maintenance Cost | Service Life (yrs) | Sinking Fund | Interest Rate | Override Default Rate | Annualized Cost |
| Maintenance & Inspection | ||||||||
| Hull and Deck Structure | $100,000,000 | 1% | $1,000,000 | 40 | $386,016 | 8% | 8% | $1,386,016 |
| Mooring system | $15,000,000 | 1% | $150,000 | 20 | $453,639 | 5% | $603,639 | |
| Fuel System | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| Ballast System | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| Fresh Water System | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| Waste Treatment System | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| Navigation & Communication | $1,000,000 | 1% | $10,000 | 20 | $30,243 | 5% | $40,243 | |
| Lifeboats & Lifesaving Equipment | $1,000,000 | 1% | $10,000 | 20 | $30,243 | 5% | $40,243 | |
| Safety & Firefighting Systems | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| HVAC System | $1,000,000 | 3% | $30,000 | 20 | $30,243 | 5% | $60,243 | |
| Residential modules | $17,280,000 | 3% | $518,400 | 40 | $143,047 | 5% | $661,447 | |
| Deckhouse structure | $15,000,000 | 1% | $150,000 | 40 | $124,172 | 5% | $274,172 | |
| Gensets (two @ 1000-kW each) | $1,000,000 | 5% | $50,000 | 20 | $30,243 | 5% | $80,243 | |
| Cooling System (FW & SW) | $1,000,000 | 3% | $30,000 | 40 | $8,278 | 5% | $38,278 | |
| Batteries | $1,000,000 | 5% | $50,000 | 10 | $79,505 | 5% | $129,505 | |
| Power Distribution and Control | $1,000,000 | 1% | $10,000 | 40 | $8,278 | 5% | $18,278 | |
| Corner towers, common areas | $1,250,000 | 1% | $12,500 | 40 | $10,348 | 5% | $22,848 | |
| Roof top areas | $2,750,000 | 1% | $27,500 | 40 | $22,765 | 5% | $50,265 | |
| Helideck | $1,000,000 | 1% | $10,000 | 40 | $8,278 | 5% | $18,278 | |
| Floating Pier | $2,625,000 | 5% | $131,250 | 20 | $79,387 | 5% | $210,637 | |
| Revolving cranes | $1,500,000 | 1% | $15,000 | 40 | $12,417 | 5% | $27,417 | |
| Supply/Transport Boat (optional) | $5,000,000 | 5% | $250,000 | 20 | $151,213 | 5% | $401,213 | |
| Recurring Costs | ||||||||
| Insurance | 1% of total construction | $186,597,000 | $1,865,970 | |||||
| Licensed officers – 1st Officer | 2 | $48,000 | salary | $96,000 | ||||
| Non-licensed crew – Bosun | 2 | $24,000 | salary | $48,000 | ||||
| Non-licensed crew – Seaman | 4 | $18,000 | salary | $72,000 | ||||
| Supply Boat – Charter -Trips per year => | 26 | $6,000 | cost/day | 1 | day/trip | $156,000 | ||
| Fuel Costs | ||||||||
| Diesel Generators – Avg power, kW => | 500 | 0.072 | gal/kW-hr | 8,760 | hours/year | $4.00 | per gallon | $1,261,440 |
| Supply Boat – Charter -Trips per year => | 26 | 3,000 | gal/day | 1 | day/trip | $3.00 | per gallon | $234,000 |
| Supply/Transport Boat (optional) | 104 | 120 | gal/hour | 6 | hours/trip | $3.50 | per gallon | $262,080 |
Total square footage: 230,800
Annual maintenance per square foot: $36.22
Average apartment size: 640 sq. ft.
Monthly maintenance per unit: $1,932
Annual maintenance per unit: $23,181
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Recruiting Collaborators
If you believe you can help The Seasteading Institute actualize these plans, or provide us with a lower bid on any of the semi-submersible components, we would love to hear from you.
