Costs of Floating Breakwaters

As introduced in the book by Patri and Wayne, Breakwaters are really important for ocean colonization: they present significant cost benefits which are essential to make an ocean community of a certain size, not just a single fancy hotel or business park. It is also a subject being discussed in the engineering forums.

The advantage of using a breakwater is that it eliminates all the problems caused by waves. Structures become much cheaper, safer, and easier to expand, seaplanes can land, and cargo is easier to offload. But to do this, you must dissipate the tremendous energy found in ocean waves and do it continuously, for years on end, even during severe storms. If the breakwater fails, suddenly your structures must face waves they were not designed for, which may be disastrous. In principle, the floating breakwaters are the most suitable ones, as the artificial ones resting over the sea bottom are limited to a few meters in depth.

The problem as introduced in a previous blog post is the cost. How much would it cost to establish a floating breakwater in the ocean? Here we show some numbers.

According to FDN Engineering, the floating breakwaters can be categorized into 3 types:

T-Block, used only at locations with water depths up to 6 meters or wave heights up to 1.1 meters.
U-Block, recommended for more severe conditions with water depths up to 12 meters or wave heights up to 2.5 meters.
Heavy Duty U-Block, for even more extreme conditions.

They are shown in the graph below:

The table below gives an overview of the design possibilities of these types of floating breakwaters. These numbers are only indications, as the exact numbers depend on the local conditions and the clients’ wishes. The cost estimate is an estimation of the direct costs of the build of a breakwater, including anchorage and installations, excluding VAT. 

Heavy Duty U-Block
up to 20 m
up to 30 m
50+ m
3 – 4 m
4 – 7 m
7 – 18 m
Height (total)
3 – 4 m
4 – 7 m
7 – 18 m
Water depths
up to 6 m
6 – 12 m
> 12 m
Wave heights
up to 1.1 m
1.1 – 2.5 m
> 2.5 m
Cost estimate
3.000 € / meter
€ 5.000 € / meter
10.000 € / meter

In any case, floating breakwaters are still an unsolved the problem for seasteading purposes because the biggest Heavy Duty U-Block was the semi-floating jetty installed in Monaco hinged to the coast, set in water 55 m deep and with a design maximum wave height of 4.9 m. Also, as already mentioned, according this thesis, for water depths over 60 m the cost of the floating breakwater is unknown. We reproduce here the graph from page 15 of that thesis. The line of cost/m finishes precisely in 55 m, the water depth reached in Monaco, with a cost per meter around 75.000 €.

It still seems a sizable engineering challenge to establish a floating breakwater in the middle of the ocean outside of the EEZ. But on the other hand, and as it was suggested in the previous blog post and in the engineering forum, installing them in a seamount in benign waters might be a possibility.




17 thoughts on “Costs of Floating Breakwaters”

  1. I’m sorry, but this doesn’t make any sense.

    1) A floating breakwater will cost the same regardless of whether it’s moored in 10m of water or 1000m.  The costs for materials, labor, etc will not change.  So you need to simply calculate the size of the required breakwater and its design, then come up with a cubic meter volume of concrete needed.  Calculate labor costs and you have the cost of the breakwater.  The only thing that will vary depending on depth is the mooring system.

    2) Why on Earth would it cost €50k to moor in 30m of water and €90k to moor in 40m?  Are you telling me that an extra 10m of line costs €40k?  I find that very hard to believe.

    When calculating the cost of any floating breakwater you need to break it down into two pieces: the cost of the physical breakwater itself and the mooring system.  That is the only way to get a reasonable estimate.

  2. Yes, you are totally right, as FDN Engineering says:

    the cost estimate is an estimation of the direct costs of the build of a breakwater, including anchorage and installations, excluding VAT.

    That is the reason why it depends on water depth: because anchoring/mooring and installation are included. Of course, it would be great to have each of these costs separately!!

  3. I have to agree with

    if not what is the argument for the cost excess.

    (history of deep water anchor handling)

    Anchoring should always be in the range of a few percent of the structure building cost .

    A related discussion is here:  Monaco floating Breakwater

    My general course of action in project management would be to mistrust frontpage cost info until the cost structure can be explained with logic arguments and checked with third party cross reverences.

    This chart looks far to “freehand painted” to be trustworthy – i would not base a business development strategy on this info.

    We should also have clear that the cost development depends very much on the specific charateristics of the anchor rig.

    Although it may be true that handling cost grows with the weight of a kilometer long chain – this is absolutly not true for neutral buoyant anchor lines which are basicly independet of water depth. (reference cousteau deep sea anchor experiments) . Cousteau anchored Calypso with polypropylen line (finger thick) in mid ocean.

    A general chart cost versus depth is in itself highly questionable – way to global – what anchor rig type we are talking about ?


    European Submarine Structures AB




  4. the cost estimate is an estimation of the direct costs of the build of a breakwater, including anchorage and installations, excluding VAT.

    I just don’t see the purpose in releasing a mixed cost graph like this.  Obviously FDN Engineering know the estimated individual costs of each component, otherwise they wouldn’t be able to calculate the total cost estimate!

    A floating breakwater needs to be treated as two seperate projects: the physical structure itself and the mooring system.  The benefit of doing it this way is that you can tweak each piece for the given situation.

    For instance you might want to look at multiple anchoring systems like VLAs, suction piles, etc….each which is going to have different installation and maintenance costs.

  5. Also when we are talking about breakwater cost – which one we are talking about?

    Are we talking about “net like” breakwaters – like the tire weave, a solid piece of floating concrete type marina walkway, chain beakwaters like the blue one below, second use breakwaters lik a pelamis field, submerged tunnel breakwaters – or which of the dozends of options for wave atenuation that have been discussed on the forums…

    Or are we talking about breakwaters so big that the breakwater IS the seastead – as performed in the Monaco Breakwater where the Breakwater contains a park house, a shopping mall, several buildings  etc….

    We could probably start with something like the floating marina below – using a single “hard breakwater” in a unidirectional wave ambient. Maybe a triangular configuration? – and end up something the size of palm dubai…




    European Submarine Structures AB

  6. Ellmer, the costs shown are related to real costs of real floating breakwaters already built. I think that the one in Monaco designed by FND Engineering is the biggest one, and it was built attached to the coast, in the benign and shallow waters of Mediterranean Sea.

    Of course, it could be great for seasteading purposes to find examples (and their costs) of other floating breakwaters built in deeper waters, in more harsh enviroments, and not attached to the coast.

  7. The monaco breakwater was built in Algeciras Spain and towed to Monaco – so it did very well floating in the high seas during a 1000 mile voyage. (video building of the breakwater )

    The waters of the mediterranean Sea are anyything less than benign due to the temperature differences of surrounding landmasses that make storms much worse. (video waves in Monaco)

    The rocky coast of Monaco is a quite storm exposed and hazardous place for ships – some of the wildest “storm against coast” videos you can find are from there…

    The general idea that deeper water is equal harsher environments is not acertive – Cape Hoorn is shallow water – that IS what makes the hoorn a dangerous place due to steep breaking waves – hazardous for ships.

    Example of floating breakwater proyect study for LNG tankers

    Building and floating out of the Ekofisk breakwater and tank  in the North Sea designed for 30m wave height.

    Floating moored structures that have breakwater funtions miles out in open sea. (Adriatic LNG, Nkossa)

    Structures of thousands of tons moored in deep water (more than 2000m) in industrial scale.

    I would suggest to step away from the theory that a floating breakwater is a extreme special case never done anywhere – basicly any structure at sea works as breakwater and wave attenuation device.

    Just look at the wave attenuation of ice fields, kelp fields, mangrove roots, even oil spills, etc…

    I think the postulation that a floating breakwater is a “engineering challenge” needs to be “UNPOSTULATED” to make the seasteading proyect move forward.

    The cost of a floating concrete structure of any kind should be in the order of cost of “cubic meter concrete” of a landbased construction site. As the building and forming process is almost identical – especially if the structure is really big.

    The cost of the mooring device should be in a order of a few percent of the structure cost. I would take the ratio structure / mooring cost of the oil industry and reduce it a bit as the position tolerances for seasteads are far less stringent so the anchor rig can be more economic.

    I would also crosscheck cost data with general civil engineering – and avoid situations where single source engineering firm data  get a strategic postulate status for the seasteading movement…

    A structure should not fall out of a general frame of 1200USD per squaremeter floorspace (which is average building cost in europe UK) (equivalent to 2,5 cubic meter of living space at 2,5m room height)

    Having the volume of the structure this cost check should be easy.

    In general the structure cost should not fall out of the frame of 480 USD (367 Euro) per cubic meter.

    We have handled projects at 331 Euro per cubic meter even for concrete hulls capeable to submerge hundreds of meters and with complicated forming in blimp shape curves.

    So building what is a simple concrete box with breakwater function in that cost frame should not be a big deal. Although it may be enourmous in size like the existing floating structures below. (Nkossa, Adriatic LNG, Rion, Glomar Beaufort, etc…)



    European Submarine Structures AB


  8. AUV gliders demonstrate that active station keeping does not have to be an energy expensive process.


    A breakwater composed of spar seasteads with variable buoyancy could easily use solar collectors to passively generate energy, and when their location has drifted too far, flood their ballast tanks until they reach operating depth before purging their ballast tanks and modifying their center of balance/control surfaces/geometry in order to “cork” back to the surface at their intended destination.

    To manage such a swarm at depth, it may be advantageous to reel in the lines lashing them together and pack them together like pencils in a rubber band.

    If their leading edge surface area geometry were ring/torus shaped then that seems like the ideal pressure housing geometry to stabalize their “flight”, and offering the flexibility to make a “pack formation”.

    Tensairity would be one means by which such a swarm could be held in a relatively stable formation, with the desired shock absorbant  qualities which would be necessary.

    We could call it “Endor.”

    I guess my point is that if anchor lines are the single largest expense in deep water floating break waters, cut the anchor and resort to station keeping.

    The geometry of these breakwaters seems to be simple enough and any shape which is strong enough to withstand tidal forces will have a dampening impact. 


  9. The question of whether a breakwater structure should be moored or use dynamic positioning (DP) is mostly a matter of cost.  (No final numbers so no final verdict.)

    The advantage of dynamic positioning is that you have flexibility of moving the structure anywhere you want while the disadvantage, as you have eloquently pointed out, is that mooring costs are essentially a one time cost.

    I agree with you that positioning costs look like they will be much higher than mooring if done using diesel/electric DP but if most DP can be handled by many small hard sails then the equation might tip back toward DP.

    I have done a “Reverse Cost Analysis” on the cost effectiveness of a breakwater structure by lineal ft.  The breakwater structure I had in mind was a pneumatic concrete structure that is 30’x15’x18′ for each unit.  It should handle most waves and it would be 30 lineal ft on sea side with a minimum of 40 units making a small breakwater square.

    I made a number of assumptions including how much space each seastead should take inside the breakwater and the arbitrary number of $100,000 per seascape in capital costs.

    When talking cost per seastead, I am only refering to the breakwater cost, not the seastead cost itself.

    PDF Analysis

    Here are some of my conclusions:

    • If cost is $100,000 per stead then cost per lineal ft of breakwater with 15 steads would be ~$1,000 per lineal ft
    • if cost is $1,500 per lineal ft then 32 steads would have to participate at $100,000 each
    • If cost is $2,000 per lineal ft then 50 steads would have to participate at $100,000 each
    • At $3,000 per lineal ft 50 steads would have to participate at $150,000 each instead of $100,000 (not shown) 
    # Steads Investment Cost/Ft
    12 150,000 2,000
    20 115,000 2,000
    25 100,000 2,000
    • The cost per lineal ft of breakwater is critical to the feasibility of building it
    • The number of people who have to participate and the likelyhood of it being feasible are inversely proportional
    • This is a backward cost analysis. I don’t know if an adequate breakwater can be made for $1,000 or even $3,000 per lineal ft

    David Clark

  10. Constructing breakwaters that offer proper protection in particular at the high seas will be challenging to say the least – technically as well as economically.

    My question is why bother trying to control the ocean?  Who would want to invest or live on board a structure whose (only? main?) safeguard is a floating breakwater? In particular when we already have access to floating structure that can resist any weather at any ocean location?

    Would it not be worth considering to accept a somewhat larger range of motion and opt to base an offshore structure on the shape of a normal large comercial vessel. For large vessels the motions are largely decided by the shape and the degree of stability.

    A structure of the dimensions of a VLCC of say 250.000TDW could remain stable and livable throughout all weather conditions, and probably be significantly cheaper to construct and maintain than the platform consytructions based on the offshore industry standards. In particular if built of concrete rather than steel.



  11. Hi Anders, the rationale for a breakwater is that it reduces the wave-handling requirements of structures located within it.  And the area inside is a square of the linear dimensions whereas the breakwater itself is linear.   Therefore it offers a potential reduction in cost.  However as noted, if the breakwater fails for example during a large storm, the less capable structures inside may risk sinking.

    Regarding mooering (anchoring), the cost of mooring in deep water is probably a much greater proportion of system cost than anchoring a much smaller structure in relatively shallow, protected waters near shore.  Miguel has some research about this already:

    seems to show that the cost of dynamic positioning, i.e., lots of fuel burn, is lower than the cost of mooring.

  12. It’s impossible to talk seriously about the cost of breakwaters without first laying out the requirements that the breakwater is intended to address.  Depth of water, worst-case sea conditions the breakwater must withstand, and — above all — worst acceptable wave conditions that must be be guaranteed in the shelter of the breakwater.

    Depth of water does matter a lot, even for floating breakwaters.  It’s not just because it affects the cost of mooring, but because it affects the character of the seas that the breakwater will be expected to block.  In the deep waters of the open ocean, there may be long-period swells a quarter mile or more between crests with periods of 15 to 30 seconds.  If the breakwater is required to block such swells — well, good luck.  

    If the swells have a maximum height of 30 meters from trough to crest — not impossible in a sustained gale — a floating breakwater able to block them completely would need a cross section of around 100 meters high by 400 meters wide.  25 meters of its height would be freeboard, and 75 meters draft.  The 400 meter width is needed to prevent wave-induced movement of water under the breakwater from regenerating the swells on the sheltered side, and to provide sufficient inertial mass and lateral rigidity to serve as an “immovable object” to the swells.

    A floating breakwater of that class would not be simply a breakwater; it’s a linear city!  Its cost would probably work out to something on the order of a $1 million per meter.  But is it necessary to block long-period deep ocean swells entirely?  Of course not, if all you’re looking for is a sheltered place to moor houseboats.  But if you want to have rigid rafts with large surface areas and minimal cost per area, then maybe it is.  Any long-period swells incompletely blocked would break such rafts like a child snapping a slab of peanut brittle.  OTOH, if you go with hundreds of flexibly connected smaller rafts, you can have all the cheap surface area you want, and they’ll simply ride over the long-period swells.  But you have to define the sea environment you’re prepared to tolerate.

  13. I remember a long time ago there was an experiement using subsurface buoys to break up the waves.  The buoys were arranged in a grid pattern underwater tethered to the bottom.  The theory behind it was the round shape of the buoy below the water’s surface would break up the harmonic wave pattern. 

    As you know, a wave is not necessarily a body of water moving along the surface but an harmonic wave pattern that moves the water up and down in place like a Tsunami.  While wind and tides generate waves, what is actually happening is the wind is impressing a harmonic energy signature upon the water’s surface where this energy transfer causes the surface of the water to vibrate at a harmonic frequency of sorts.  Placing a buoy below the surface interrupts that harmonic frequency.  This concept might be a lot cheaper than solid floating breakwaters plus allow shipping to pass through with minimal obstruction.

  14. I’m no expert, but I do have a few outside the box ideas now and then. Reading about breakwaters this morning got me thinking. Breakwaters are a new concept for me, so I hope you’ll excuse me if my ideas seem naive or aren’t viable.

    I have some experience in construction, and have wondered a long time about the possibilities of using various plastics such as closed cell foams to form structural members instead of the traditional concrete/stone, steel or wood. I think plastics could be the ideal material for building breakwaters because of their flexibility, resistance to corrosion, relative strength and light weight . The initial costs may be higher than the costs of traditional building materials, but could be offset by lower maintenance costs, longer expected useful life, transportability, etc. The biggest disadvantage I can see besides cost is vulnerability to fire.

    I have a vision of a breakwater made of a plastic shell topped with translucent materials and filled with soil. Essentially a series of floating terreriums used to grow whatever crops might be in greatest demand, whether that would be fresh foods, flowers, medicinal or culinary herbs, landscape plants, a botanical garden for tourism, or a research lab. The surface could be used for any number of activities as long as sunlight remains relatively unobstructed.

    Alternately, I wonder if a series of turbines or other mechanical devices used to power generators could act as a breakwater and if this could be cost effective.




  15. There’s a lot of energy in waves. Perhaps wave energy converters would soak up some of that energy before it hits the breakwater, and also provide electrical power?

    I think that a traditional breakwater in the deep ocean is the best way to go for political reasons. Anything you can do to mitigate the chances of a nearby country claiming your seastead (a-la Minervia). It’s more expensive, but you may be able to balance that against the cost of living in a first-world country.

  16.  In the deep waters of the open ocean, there may be long-period swells a quarter mile or more between crests with periods of 15 to 30 seconds.

    It seems to me that long period swells wouldn’t pose any danger at all to a seastead (since they aren’t cresting, and since the entire community is lifted basically at the same time).  Its the short-period and tall waves that pose a danger.


  17. There’s a lot of energy in waves. Perhaps wave energy converters would soak up some of that energy before it hits the breakwater, and also provide electrical power?

    I imagine if someone built a deep sea community, there would be a strong need for independant electricity.  So, I’d think some sort of wave power plant or solar power plant would be built pretty quickly.

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