Cost of building a floating construction facility


I am trying to figure out how to build a cheap, effective floating manufacturing platform.

One idea is to start with 2 120’ long hulls possibly ferro concrete, what ever is the cheapest. Then cover the hulls with 12 60’ long shipping containers making a flat working surface of 120’ x 60’ on top. I bet that much could be put together for around $100k.

Add a covered and enclosed 20’ tall structure on top with lifts on the beams turning them into cranes, add a generator, storage tanks, electrical etc. for another $100k and you have a finished facility with an office and living quarters.

On land in Florida next to the ICW that facility would cost about $1.2M and to rent it would be about $10K a month plus expenses and taxes. That would give the facilities owner about an 8% return on their investment.

Charging $4k a month for the floating facility would generate close to a 20% return on the investment. Anything better than a 12% return on their money will make investors sit up and take notice. Of course we are dealing with a depreciating asset (boat) vs an appreciating asset (land) so that needs to be taken into account.

It would need a calm mooring and access to a dock and few legal restrictions.

I would be willing to pay $5K a month to lease the facility for a couple of years and I know other people who would be very interested in the same thing. It would even be better if 4 of these units were rafted together making group projects easier and faster.

I am also sure that there are even better cheaper design ideas than this.


Former member @katontri has similar ideas at a smaller scale.

Her inventiveness was basically shut down in here by the male chauvinists that poopooed almost everything she said, whether critiquing a poor concept, supplying alternative ideas, presenting her own vision, etc.

Her ideal would be operating such a maker/builder operation, to turn out smaller family-scale Seasteads.


Honest criticism is important in avoiding mistakes, it should be taken for what it is worth.

What this site is sorely lacking is honest criticism especially engineering criticism, anyone else notice the absence of engineering expertise here? No NA is going to have anything to do with this site because it would hurt their reputation.

Always remember though that all big successes are in spite of the critics, the critics are always wrong. The trick is to figure out where the critics are wrong : )

(noboxes) #4


  1. You have already designed it as a catamaran?
  2. I am curious why you want so much deck space first thing. Or is it the weight carrying capacity you need?
  3. I bet no one here who would build it, has the money to build it, or even can build it.

(Wilfried Ellmer) #5

@Talador |

A good starting point is always checking what is “out there already”

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(Wilfried Ellmer) #6

Cost Analysis Floating Structures

My analyis (short version) of cost per square meter of floating structure derived from several dozend real world pilot projects is here:

the range is:

USD 20 / square meter | for the poor man´s floating island methods.

USD 50 - 166 / square meter | for the ultra light freeforming methods | walls of 5 mm are possible | check on “Floating Rock”

USD 150-300 | for medium methods wall thickness 5 cm | dot printing | special cast | and lamination methods | projected concrete | ferrocement |

USD 300-800 | for heavy cast methods | the usual industrial boxy stuff | standard marine concrete engineering form and cast.

All the above prices must be understood as derived from a specific pilot project. They are money input (into the project) / square meter output (at project end) - figures include all costs that are asociated to the project - not only materials and labor .

Singapore Landfill operation come at USD 700 per square meter - so floating real estate is definitly competitive on the existing market.

Real Estate Developer @tamenta would consider USD 500 per square meter (USD 50 per square foot) competitive ground with land based real estate developments.

Here in the Cartagena area we have real estate prices for shoreside real estate that suggest that we can sell a floating real estate square meter at a market price of about 102 times the money it cost our group to build it.
That has "GOOD BUSINESS" and "Investment worthy" written all over the development horizon.

(Wilfried Ellmer) #7

The cheapest is poor man´s floating island

Then comes Floating Rock


Sure but a floating rock isn’t very useful. My suggested floating factory would come in around $15 a square foot or $150 a square meter because you get to count the area inside the containers too.

All of which is a fraction of what building on land costs.

The big difference though is that land is an appreciating asset where boats are a depreciating asset. What that means is that the end of the day an investor can recoup 100% of their real-estate costs and that is why financing is so easy for real-estate.

Also Labor often times benefits from the insurance and taxes that their employers pay depending on the system they are in. Getting talented labor could be a problem.


I think I understand the benefits and pitfalls of concrete. The coefficient of expansion (cracking) seems to be a problem, every concrete structure I have ever seen has expansion joints. . . For loading under compression like a foundation or a road it can’t be beaten for cost and durability. But when it comes to tension it relies solely on the reinforcement, so in a boat which alternates between compression and tension the concrete is mostly useless, it is better to simply use the reinforcement material for the entire structure.


Not entirely true. There are ferrocement hulls still in use from both WW-I and WW-II, unlike other materials. Largely, routine care and quality of manufacture make the biggest difference in durability.


Some of the old Roman roads that used concrete are still in use today too : ) Rocks last a heck of long time.

The problem is length and deflection, something that is 10 feet long and stays in the elastic deformation range is immortal while the same material that is 100 feet long will deform in the plastic range and fall apart. Concrete has an extremely small elastic deformation range consequently limiting its spanning capability.

I don’t know what the length limit is but there are a whole host of materials that are far superior to concrete when it comes to span length and a Hull is nothing but a span or a beam.


We’ve covered this several times. Perhaps you should study things a bit more…
The Powell River Floating Breakwater
Of all the concrete ships built during World War I and II, only 10 are known to still be afloat. These ships form a massive floating breakwater on the Malaspina Strait in the city of Powell River in British Columbia, Canada.

The breakwater was constructed to protect the logging pond of the Powell River Company pulp and paper mill (later purchased by Pacifica Papers).

While nine of these ten ships were built during the Second World War, the tenth ship, the S. S. Peralta, is the last remaining WWI concrete ship afloat.

In December of 2000, the mill was downsized as the result of a corporate merger between Pacifica Papers and NorskeCanada. The mill no longer processes raw materials, so they were planning to remove a few ships from the breakwater. The company changed its mine and decided to keep all ten ships, but rearranged them.
The Peralta is still afloat as part of a breakwater for a pulp and paper mill in Powell River in British Columbia, Canada. She is the last ship of the World War I fleet still afloat. At 420 feet, she is also the largest concrete ship afloat.

In December of 2000, the mill was downsized as the result of a corporate merger between Pacifica Papers and NorskeCanada. The mill no longer processes raw materials, so they were planning to remove a few ships from the breakwater. There was discussion of sinking the Peralta as an artifical reef; however, the company changed its mind and decided to keep all ten breakwater ships. The Peralta is safe for now.


I was trying to be kind, there seems to be a lot of effort invested in FerroCement construction here and I have been looking at it with new eyes.

Let me turn the question around. They started building Ferrocement ships during the war because of a steel shortage. After the War they immediately quit building them.

Why? If concrete was equal to Steel, and it is obviously cheaper, why aren’t all the ships in the world built out of ferrocement? I can list 3 or 4 very obvious show stoppers and never see them mentioned, why is that?

Is it possible no one here knows why concrete is not an ideal material for boat or barge building?

(Wilfried Ellmer) #14

Don´t shoot so fast my friend … floating rock can be formed to any kind of building you can imagine…check on the range of feasible structures at Matias Volco´s site…

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Of course you can also make a extreme light, fast, and big CATAMARAN out of it…and build it directly on the watersurface - no landbased shipyard required. | You don´t need to protect the material from rain nor seawater - at any point of the construction (Plywood and vac infusion are much more delicate …)

We should talk about that… @Talador

@Elwar | Is a Live Aboard Catamaran still on your interest horizon - we might have a project… now that you retired and bitcoin soars…

(noboxes) #15

Personally, if i went that near route, it would be with geopoly and basalt reinforcement. That said, perhaps your question should be turned around, perhaps the large boat or barge is not the ideal form to be making with concrete? This does not obviate making other forms from the material of choice. You said a boat hull is a structurally span, perhaps if you launched a steel span with appropriate cement floatation forms under it, you’d have something to consider?

Also, you said in regards to the WW2 ships, “If concrete was equal to Steel, and it is obviously cheaper” , i don’t think it was equal or cheaper. If you look at those ships prior to the forms going up, there’s so much rebar that you cannot see thru it. There was more than one reason those ships were built, and a few of the variables was the rebar factories went idle during the war while plate steel factories initially were not cranking out steel fast enough, rebar was made of cheaper recycled unknown strength steel, and generally unskilled labor could be used to place the rebar vs equipment and skilled labor to place conventional ship parts. The downside to the concrete ships was they crack when bumped and are virtually unrepairable (cement isn’t geopoly), the steel rebar rusts (it isn’t basalt), and they drink more fuel because they are heavier (displace more water). I’d hate to see what one would look like after 10 years of full commercial service with a couple big diesels pounding away inside one.

(Chad Elwartowski) #16

Not for now. Right now my focus is on a seastead in Tahiti.

Living on a boat was always my backup plan if no seastead tech gets built.

(Wilfried Ellmer) #17

@Elwar |
Good luck on that - keep me informed how it develops…

Best wishes,



I am not adverse to the concrete hull idea especially for a displacement hull which I prefer

Yep that is extremely interesting to me.


Sure, but velocity for a displacement hull is largely dependent on waterline length, the longer the hull the better. A couple of floatation points is exactly the opposite of what you want for a boat. It would be much better to shape the Steel reinforcement into a hull : )

Actually the problem is elongation or the difference in elongation between basalt rebar and concrete concrete. The reason epoxy and fiberglass or carbon works so well is because epoxy can stretch more than the fiberglass, any failure will be from the glass which is stronger than steel.

Even with a polymer concrete the steel or basalt elongates more than the concrete. That means even vibrations like waves over time will separate the concrete from the reinforcement. It is simply a matter of ‘when’ not ‘if’ the separation is going to occur.

Yeah you can engineer it to minimize the problem, but it is hard and adds weight and cost, etc.

Always remember the structure is generally only about 10% of the total cost. Perceived value is also very important and concrete is low in that regard.

The business to be in is where the costs are low and the perceived value of the product is high. Software anyone?


The expansion rates of the Basalt Composite Rebar seem note inline with the characteristics of Cement. Notice, I said cement… A Ferrocement hull is plastered with a cement mixture, not ‘concrete’. In addition, the originals were vastly overbuilt, thus heavier than necessary, as well. Do the research, before making ng your comparisons, don’t just base it on comparing a slab of concrete to a slab of steel (of which steel has the higher density for equal volume).

One big drawback of Ferrocement’ has been the ferro portion… It corrodes, can have electrolytic corrosion, even buried in concrete, or cement, leading to spalling and structural failure.

Another is the difficulty of bonding OPC products, for patching, which never gains the same strength as the original structure before damage and patching. Geopolymer has different properties, bonds readily to itself, has a very Basic chemistry, reducing and preventing corrosion, while composite rebar eliminates corrosion, has far lower density than steel, exhibits more of the desirable characteristics for elasticity, tensile strength, etc., w/o work hardening in a flexural situation.

There are many reasons, well expounded on in this forum, for the material choices of composite rebar and geopolymer.

I’ve personally experimented at producing some. Given time and lab access, I could potentially produce a geopolymer formulation that cuts the price of OPC by 1/3-1/2, as well.

In addition, Geopolymer has the potential to last hundreds, even thousands of years…