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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 Maintenance $8,359,666

 

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

 

Photo Gallery:

 


Top view

Outside close-up

Outside wide view

Courtyard/restaurant view

Double unit – bird’s eye view 

Single residential unit – side view

 

 

 

 

 

 

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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.

 

 

 

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