Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Dolosse – a South African invention used over the world

thisbugslife.com

Post reply on HN
Print view View original

31–40 of 43 posts

Re: Dolosse – a South African invention used over the world

#31

Post by conductr »

markdown wrote: post #17
nusq wrote: post #15

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 pr…

> reinforcement with rebar is almost always a bad idea in ocean conditions While a little more costly, 316 stainless steel should work just fine.

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.

Re: Dolosse – a South African invention used over the world

#32

Post by aaroninsf »

lazide wrote: post #25
markdown wrote: post #17

Earlier quoted context omitted.

> reinforcement with rebar is almost always a bad idea in ocean conditions While a little more costly, 316 stainless steel should work just fine.

‘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

Re: Dolosse – a South African invention used over the world

#34

Post by aaroninsf »

sgt wrote: post #26
cookiengineer wrote: post #16

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.

Re: Dolosse – a South African invention used over the world

#35

Post by lazide »

aaroninsf wrote: post #32
lazide wrote: post #25

Earlier quoted context omitted.

‘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.

Re: Dolosse – a South African invention used over the world

#37

Post by sgt »

aaroninsf wrote: post #34
sgt wrote: post #26

Earlier quoted context omitted.

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.

Another thing is that you need a lot fewer of them to stack to get the same effect. So cost saving.

Re: Dolosse – a South African invention used over the world

#39

Post by silves89 »

nusq wrote: post #15

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 pr…

Thanks for this background! I encountered dolosse or something dolosse-like at Praia da Ilha de Tavira, in the Algarve, here: https://www.google.com/maps/place/Farol+de+Tavira+Molhe+Oest...

Re: Dolosse – a South African invention used over the world

#40

Post by RetroTechie »

bix6 wrote: post #29

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…

> coastal armoring in general does not work as it does not prevent erosion.

Not that simple. Example: east of Lauwersoog (north shore of the Netherlands) there's a dyke reinforcement project underway. Roughly 2/3 of the dyke's seaside is covered with regular rows of interlocking concrete blocks (~25 x 25 cm top view). At the base of the dyke, there's stone rubble to dissipate wave energy. These are heavy stones: 100s of kg each on average. But loose - some even wobble if you step on them! There's probably some other things in there like layer(s) of geotextile & such.

I'm pretty sure if those rubble stones weren't there, waves would 'eat' some rows of the smaller blocks, wash away a few metres of sand, then rows above would collapse, expose more sand, etc.

So it's not like those stones aren't doing anything.

In other places on the Dutch coast, it's more common to pump sand onto the beach every X year to replace what the sea eroded. 'Must read' in this context:

https://en.wikipedia.org/wiki/Sand_engine

TLDR; wave patterns, coastlines & what's behind them are different. So are strategies to protect them.

Post reply on HN