Breakwater Design

(Larry G) #1

Chart of breakwater type to wave period and height

US Army Corps of Engineers: Engineering Design Guidance for Detached Breakwaters as Shoreline Stabilization Structures

US Army Corps of Engineers: Functional Design of Breakwaters for Shore Protection: Empirical Methods

US Naval Academy: Wave Interactions with Vertical Wave Barriers

What about focussing on breakwaters?
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(Larry G) #2

The docks on our marina on the Columbia River (draft a few inches, and side-walk width) do a decent job of breakwater for those moored about half-way in, the ones on the outside closer to the channel get waked a lot more. But average wave height there is a few inches.

This would seem to indicate that floating breakwaters won’t be very effective in ocean waters with even small swells. There’s been a lot of discussion here over the year about floating breakwaters, but not much empirical evidence presented on this topic by anyone with a marine engineering background.

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(Matias Volco) #3

@thebastidge Insightful observations both Churchill and the Prince of Monaco should be aware of!

1944: Mulberry harbour, “Marine Cluster” built in less than one year, inevitably discussed throughout less than seven years.

2002: Monaco Floating Breakwater

During times of war morality is inverted and the extraordinary is temporarily permitted by society (usually for worse, more info about it here )
With Ekofisk being floated to location and much later the Monaco pier extension it took between 30 and 70 years for this technology to be applied for civil purposes, but the technology has existed for decades. Let’s hope by 2044 we’ll have mature trees growing in floating gardens of peace sheltered by floating breakwaters perhaps like the ones pictured in this post.

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(Larry G) #4

“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 €.”


Some concrete ships have been used as civilian floating breakwater here and here. I have suggested the recovery of sunken ships, turned upside down, so the bottom of the ships can serve as beaches and deep-draft floating breakwaters in the open ocean.


It should be noted that the moorage fees in Monaco are among the highest in the world. The 30 mega-yacht berths run 1200 Euro per day, about half a million per year. Fees go up for local events. This article mentions that someone paid 15,000 Euro for one night there during the Monaco Gran Prix.

(Larry G) #7

Parameters for the construction of a breakwater


This is a fine example of designing to fight against the ocean forces. Especially for seastead breakwaters, the maintaining an absolute fixed position in the water isn’t required, altho it’s somewhat important to not collide with the seastead, or hit a dock between the breakwater and the seastead. Ergo, allowing the breakwater to be temporarily out of position as a way to shed load off mooring lines, should be investigated by seasteads. There’s numerous ways to do this.

(Larry G) #9

Floating Tire Breakwater

And another one

and another


I think one important thing is to define the purpose of the breakwater.

I know in a harbor, the breakwater’s purpose is to shelter boats from high waves; so the boats don’t crash together or the docks fall apart. In a harbor, buildings are generally not sheltered, because they are on land. This is for waves that are higher than the design capacity of the boats and docks.

A ship at sea, is outside the breakwater, and hopefully encountering waves that are within its design capacity.

So it would seem to me that there’s really two factors here; what is the design capacity of the floating city, and then, what waves might the city encounter that is beyond the capacity, that could be ameliorated using a breakwater.

Once it reaches a certain size, the city itself is a breakwater. As you note, in houseboat communities the outer row mediates the brunt of waves, and inner rows see a much different effect. So a city of 100+ floating buildings might contain an indentation to form a harbor for holding fragile sailboats or motor boats.


I am still thinking to stay out of the wave zone. There’s not a lot of ways to protect a city and some small boats if the waves hitting it are 20ft up and then 10 seconds later are 20ft down.

(Jonas Smith) #12

Since I’m not focusing on a floating seastead model, but rather a fixed gravity base structure model, I’m thinking a fixed breakwater system would be best. Something similar to deep water wind turbine systems, using either monopile (b), gravity base structures, ©, or jacketed base (d-f):

I’d aim for gravity base structures due to their strength and stability, and it has been proven to work fine in depths up to 300m. So you have gravity base supports:

Strung out in a line where your breakwater will be:

And you build your breakwater structure in the interstitial spaces:

The breakwater structure can be simple like this, giving some outside recreation space:

Or it can even integrate wave energy systems:

One major downside for this kind of system is that it doesn’t scale…you need to build your breakwater at the maximum size you will expect for the future. You can’t exactly re-float all the gravity base structures and move them out to increase the breakwater diameter. So that will need to be factored into the build.

(Jonas Smith) #13

Another option when building a breakwater for a fixed seastead structure is to build a floating breakwater system but instead of mooring it to the seafloor you attach it physically to the center fixed structure. Something like this:

If you imagine that center structure being a condeep-like structure and the ring breakwater attached via strong supports to the center structure.

This way you get the modular nature of floating breakwater systems and the rigidity and strength of an attached system. You would need to ensure that the attachment supports are strong enough to handle the stresses involved.


Floating breakwaters are a waste of money.

(Wilfried Ellmer) #15

floating breakwaters do not work as long as the elements are not signifficantly bigger than the wavelength (2-3 times) a oceanic surface floating breakwater needs to have 400m to start to be effective see Monaco Breakwater see Mullberry Harbor. On the other hand even small particles like kelp fields and Mangrove roots DO have an accumulative wave dampening effect.


Here’s the link for Kat.

I’m not sure what your video shows. No boats are damaged. Clearly the breakwater is not sized for the waves being encountered.

I suppose you could try to imply that tiny ring of barrels is supposed to help in the big storm. You would have to know the intent of the builder. So I can’t even think this is a failure of the system. Just a failure of the viewer to think that a little string of barrels is supposed to do something in a big storm. The commentary says this is not the biggest storm to hit the dock, but the dock as stayed intact for nine years.

If anything, this shows that you should size your breakwater appropriately to the waves you intend to counteract, because the breakwater doesn’t work when waves are twice that size.

(Wilfried Ellmer) #17

A row of ramform units will definitly make a great wave protection.

ramform unit family house size capeable to deal with big waves over the bow - living space and breakwater function in a single unit.

What about focussing on breakwaters?


If you know where the last two photos are from, I’d be very interested, to learn more about the conditions those were designed for. Thanks!

(Larry G) #19

Or you build the gravity base structure for dual purpose, and add more to move your breakwater outward while re-purposing the gravity base that is now inside the breakwater.

I’ve thought about this very thing as well, and one of the things that occurred to me is that a gravity base is generally designed currently to support a lateral structure above the wave zone. If you put a lot of horizontal surface “sail area” into the wave zone, you’re increasing the lateral forces tremendously over the waves and currents simply interacting with a relatively narrow cylinder. The gravity base would need to be correspondingly much heavier and wider and perhaps wouldn’t work in the same depth of waters because the leverage pushing on a tall gravity base will overcome the tipping moment of a narrow base.

(Jonas Smith) #20

This design is by a company from Norway called WaveEnergy, called a “Seawave Slot-Cone Generator”. Here are some links:

harvesting the power of the ocean
WaveEnergy - technology

According to the PDF the SSG pilot project was to be built on the “west coast of the island of Kvitsøy in an estimated 15kW/m wave climate”. Not sure how far they got with that.

The second one is a design from Japan. It’s one of the designs picked out by Dr. Philip L.-F. Liu from Cornell University and taught in his coastal engineering courses. Not sure exactly where in Japan, but here is a paper discussing the hydrodynamic characteristics of semi-circular breakwaters.

Here is PDF on Dr. Liu and his work: breaking the waves