Finnally something I have knowledge of. Dolosse were invent in South Africa many years ago, but they are only one type of concrete block for wave dissipation and protection. Many others exist and some of them are patented and require the payment of royalties to be used. Anyway, in Portugal we do not use dolosse ever. We used it once in Sines deepwater breakwater, which suffered a catastrophic collapse in 1979. The promise of dolosse is that the blocks work together because of their shape and thus the individual block can be lighter and cheaper. This does not work in practice, at least in high energy seas. The ocean is unforgiven. What happens is that if only a few blocks break the whole structure will quickly collapse during a storm. And things can break due to a series of problems and risks. Concrete is only good at resist compression stresses and reinforcement with rebar is almost always a bad idea in ocean conditions, so complex shapes are hard to make and to move without introducing unwanted stresses that reduce the design strength conditions. Other types of blocks rely mostly on their design weight and density, and the shape is just used for increasing energy dissipation and overtopping. For example, tetrapods can be moved with only compression forces on the block.
Fiberglass rebar is comparable in cost, stronger, and not subject to water/salt damage. Rusting steel expands and cracks concrete from the inside, id want to avoid that. I’m actually building a pool right now using it instead of steel.
Interestingly the author shows a photo of a spot in Cape Town where there are two distinct structures in use - close up, in the photo, are actually Tetrapods - as pointed out in other comments, these are an earlier invention from France and also used quite extensively throughout many parts of the world (including... right here where the Dolosse were invented).
Further down that jetty are structures with the actual Dolos geometry. It would be interesting to know if, specifically, those geometries were chosen specifically to be placed in those two parts of the wall as they are for specific properties, or if came down to having certain quantities made on hand and their distributions matched the shape of the wall required, or what.
You can see what I mean, this distinction in the exact location where that photo is taken on google maps, here:
Mathematically, I think they both may be tetrahedons. The Tetrapod models it by 4 lines connecting each of its vertices to its center, the Dolosse by two opposite edges connected by a line through the middle.
I’m saying “may be” because it is possible that the center “arm” of the Dolosse is too large to make a true tetrahedon. That’s a degree of freedom in the design.
> It would be interesting to know if, specifically, those geometries were chosen specifically to be placed in those two parts of the wall
My guess would be that Dolosses interlock better than Tetrapods, allowing for steeper inclines on stacks of them.
That connecting "spine" is there to improve the interlocking of the tetrapods. They can "hook" better to each other. That's the theory at least, I don't know the if it's better in practice.
> One of the earliest designs is the Tetrapod, invented in 1950. Other proprietary designs include the Modified Cube (United States, 1959), the Stabit (United Kingdom, 1961), the Akmon[W] (The Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod [ro] (Romania, 1969),[7] the Seabee (Australia, 1978), the Accropode[W] (France, 1981), the Hollow Cube (Germany, 1991), the A-jack[W] (United States, 1998), the Xbloc[W] (The Netherlands, 2001) and KOLOS[W] (India, 2010) among others.
I have put Ws next to ones with their own Wikipedia page.
In Germany (on the island Sylt) they recently removed all of these structures again after decades of them being a staple on Sylt's beaches. They were found to have no positive effect on protecting their shores.
I'm having a hard time to find a good source to quote but look for: "sylt tetrapoden" if you want to dive deeper.
I find it hard to believe they have not protective effect. You can throw pretty much anything hard with an irregular shape down and it’ll help scatter energy
Well, confusingly, the last picture on the blogpost look (to my untrained eye) to be tetrapods. Those are 'tetrahedral' (ish) shapes.
In contrast, the https://en.wikipedia.org/wiki/Dolos (plural 'Dolosse') are two tapering cylinders at right angles to each other. They have the same symmetry, but a different structure. Does that make any difference to how effective they are? No idea!
edit: When I said the "same symmetry" of course I should have said the dolos has some of the symmetries of the tetrapod (subgroup?).
A bit rude, this doesn't come across as spam but a genuine human sharing something interesting they came across. Peak old internet (2000s) content. The wiki article is very short and doesn't actually have more or better pictures.
Some people here think if it's on Wikipedia it's authoritative. Yours truly has written many Wikipedia articles, some translated into ten or more languages. I've seen how ugly it is behind the scenes there.
I miss blogs. They are omitted from searches now but are among the best internet search content. Threadinburgh is one of the best online resources about Edinburgh by far.
Bizarre hate towards someone's little blog. And it's not even LLM spam, just someone running their own WP site. By your logic I should save myself the Wikipedia verbosity and just ingest LLM output for any query I have forever.
These are cool shaped but they don’t actually work; coastal armoring in general does not work as it does not prevent erosion. Sand replenishment is increasingly the path taken. Australia has an amazing pumping system (a jetty blocked longshore sand transport so they pump it around to the other side).
There's lots of different forms and shapes of wave breakers, like the Tetrapods [1] that you can find over here across pretty much every coast in Europe.
Maybe I'm just not getting it why the Dolosse shape is superior?
Apparently the Dolosse works a lot better for high energy wave environments like coastline of SA etc. They are used here, and I am sure they considered Tetrapods and there was a reason they weren't suitable.
Finnally something I have knowledge of. Dolosse were invent in South Africa many years ago, but they are only one type of concrete block for wave dissipation and protection. Many others exist and some of them are patented and require the payment of royalties to be used. Anyway, in Portugal we do not use dolosse ever. We used it once in Sines deepwater breakwater, which suffered a catastrophic collapse in 1979. The promise of dolosse is that the blocks work together because of their shape and thus the individual block can be lighter and cheaper. This does not work in practice, at least in high energy seas. The ocean is unforgiven. What happens is that if only a few blocks break the whole structure will quickly collapse during a storm. And things can break due to a series of problems and risks. Concrete is only good at resist compression stresses and reinforcement with rebar is almost always a bad idea in ocean conditions, so complex shapes are hard to make and to move without introducing unwanted stresses that reduce the design strength conditions. Other types of blocks rely mostly on their design weight and density, and the shape is just used for increasing energy dissipation and overtopping. For example, tetrapods can be moved with only compression forces on the block.
> reinforcement with rebar is almost always a bad idea in ocean conditions
While a little more costly, 316 stainless steel should work just fine.
Or composite rebar. Basalt fiber is sometimes used. Way cheaper than stainless and just as rust proof
Fiberglass rebar is comparable in cost, stronger, and not subject to water/salt damage. Rusting steel expands and cracks concrete from the inside, id want to avoid that. I’m actually building a pool right now using it instead of steel.
‘a little more costly?’ Lulz.
316 is an order of magnitude more expensive than the crap used in rebar.
In project budgeting the material cost difference may well be relatively insignificant
Sure, but that’s not what was said.
Interestingly the author shows a photo of a spot in Cape Town where there are two distinct structures in use - close up, in the photo, are actually Tetrapods - as pointed out in other comments, these are an earlier invention from France and also used quite extensively throughout many parts of the world (including... right here where the Dolosse were invented).
Further down that jetty are structures with the actual Dolos geometry. It would be interesting to know if, specifically, those geometries were chosen specifically to be placed in those two parts of the wall as they are for specific properties, or if came down to having certain quantities made on hand and their distributions matched the shape of the wall required, or what.
You can see what I mean, this distinction in the exact location where that photo is taken on google maps, here:
https://maps.app.goo.gl/Vn3tGhM81oMqPVpm9
-33.899126, 18.412751 Mouille Point, Cape Town, 8005, South Africa
Mathematically, I think they both may be tetrahedons. The Tetrapod models it by 4 lines connecting each of its vertices to its center, the Dolosse by two opposite edges connected by a line through the middle.
I’m saying “may be” because it is possible that the center “arm” of the Dolosse is too large to make a true tetrahedon. That’s a degree of freedom in the design.
> It would be interesting to know if, specifically, those geometries were chosen specifically to be placed in those two parts of the wall
My guess would be that Dolosses interlock better than Tetrapods, allowing for steeper inclines on stacks of them.
That connecting "spine" is there to improve the interlocking of the tetrapods. They can "hook" better to each other. That's the theory at least, I don't know the if it's better in practice.
The Wikipedia article:
> A dolos ... is a type of tetrapod
but also, the Wikipedia article for tetrapod:
> One of the earliest designs is the Tetrapod, invented in 1950. Other proprietary designs include the Modified Cube (United States, 1959), the Stabit (United Kingdom, 1961), the Akmon[W] (The Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod [ro] (Romania, 1969),[7] the Seabee (Australia, 1978), the Accropode[W] (France, 1981), the Hollow Cube (Germany, 1991), the A-jack[W] (United States, 1998), the Xbloc[W] (The Netherlands, 2001) and KOLOS[W] (India, 2010) among others.
I have put Ws next to ones with their own Wikipedia page.
Neat didn't know that's what they're called you see em in Japan too "over the world" yeah
In Germany (on the island Sylt) they recently removed all of these structures again after decades of them being a staple on Sylt's beaches. They were found to have no positive effect on protecting their shores.
I'm having a hard time to find a good source to quote but look for: "sylt tetrapoden" if you want to dive deeper.
I find it hard to believe they have not protective effect. You can throw pretty much anything hard with an irregular shape down and it’ll help scatter energy
They don’t prevent erosion though which is the primary issue
Ok I stand corrected these are NOT tetrapods. Sorry for the confusion
Well, confusingly, the last picture on the blogpost look (to my untrained eye) to be tetrapods. Those are 'tetrahedral' (ish) shapes.
In contrast, the https://en.wikipedia.org/wiki/Dolos (plural 'Dolosse') are two tapering cylinders at right angles to each other. They have the same symmetry, but a different structure. Does that make any difference to how effective they are? No idea!
edit: When I said the "same symmetry" of course I should have said the dolos has some of the symmetries of the tetrapod (subgroup?).
Maybe the form variations were just for patent circumvention.
Interesting. Been to South Africa a bunch but never clocked that they were different from the more common antecedent, the tetrapod[1].
1: https://en.wikipedia.org/wiki/Tetrapod_(structure)
“Hast thou considered the tetrapod?” can finally be answered positively on HackerNews. Hail Satan.
Save yourself the blogspam, go directly to https://en.wikipedia.org/wiki/Wave-dissipating_concrete_bloc... and enjoy the whole collection !
A bit rude, this doesn't come across as spam but a genuine human sharing something interesting they came across. Peak old internet (2000s) content. The wiki article is very short and doesn't actually have more or better pictures.
Some people here think if it's on Wikipedia it's authoritative. Yours truly has written many Wikipedia articles, some translated into ten or more languages. I've seen how ugly it is behind the scenes there.
I miss blogs. They are omitted from searches now but are among the best internet search content. Threadinburgh is one of the best online resources about Edinburgh by far.
> They are omitted from searches now but are among the best internet search content
I use google search with &udm=14 to remove all AI elements in the results presentation.
Searching for "dolosse", the HN item is the 3rd link, and TFA is the 4th. They are preceded by Wikipedia, and a dolosse-manufacturer's page.
Not sure why you think "blogs are omitted from searches now".
Bizarre hate towards someone's little blog. And it's not even LLM spam, just someone running their own WP site. By your logic I should save myself the Wikipedia verbosity and just ingest LLM output for any query I have forever.
These are cool shaped but they don’t actually work; coastal armoring in general does not work as it does not prevent erosion. Sand replenishment is increasingly the path taken. Australia has an amazing pumping system (a jetty blocked longshore sand transport so they pump it around to the other side).
We could just stop building so close to shore…
Invented by Eric Mowbray Merrifield and his team, which included Piet Grobbelaar and Jack Badham-Thornhill.
The article is embarassing. Basically it says nothing but links to wikipedia. I’m saving you a click: https://en.wikipedia.org/wiki/Dolos
The blog article mentions 80 tons while the wiki article mentions 8 tons. Are they using the same definition of a ton ?
Not sure why Dolosse are so special?
There's lots of different forms and shapes of wave breakers, like the Tetrapods [1] that you can find over here across pretty much every coast in Europe.
Maybe I'm just not getting it why the Dolosse shape is superior?
[1] https://en.wikipedia.org/wiki/Tetrapod_(structure)
Apparently the Dolosse works a lot better for high energy wave environments like coastline of SA etc. They are used here, and I am sure they considered Tetrapods and there was a reason they weren't suitable.
ITT the consensus is they don't actually work better, but, were royalty free.
No idea about either, myself.