A sand bag the size of a cement bag weighs 100 lbs. Any potato chip bag with 100 lbs in it will bust open when a wave pushes it into another one if not before. Vincecate 22:22, 3 June 2008 (UTC)
- Ok, I'm not too sure about real tubes myself. It would still work if the tubes consisted of little bags, though (but the construction would be a bit more expensive). It's not exactly science, but a small child can't open a bag of chips because sealing is quite strong and heavy stuff like cement is sold in much weaker material (like paper) which still holds. And a wave is not a car crashing into the "curtain", it's an extremely powerful but gentle force. This is something that needs experimenting I guess. I'll add your comments, thanks! Joep 23:57, 3 June 2008 (UTC)
Something I have learned from talking to professional offshore engineers is that amateur analysis of hydrodynamics is often wrong. You need to think about things like resonance and vibration which are much more complicated than thinking about what happens when a single wave hits. Much analysis is done in non-time domains (like the frequency domain). Any large massive structure will block the waves, and I don't know why this one is particularly good. Certainly it is best if we can get our large rigid mass as cheaply as possible, but I don't know that sand or mud are that much cheaper than concrete. Concrete is just made of rocks, which are quite cheap per unit weight. Patri 00:04, 4 June 2008 (UTC)
- The idea is that it's a lot easier to make tubes or bags than to create big structures made of concrete and adding flotation to it afterwards. I won't deny being an amateur and I do have ideas that are plain stupid, of course. I'm just wondering if this is one of those. Joep 00:39, 4 June 2008 (UTC)
- It might be both easier and cheaper to build basic floating elements out of concrete and assemble them into a breakwater. "Bags" or tubes of concrete filled with air ? Concrete is very easy to mold into complex shapes, let's take advantage of that. I would guess vertically floating hollow cylinders, with one end slightly ballasted, just like the spar idea but scaled down and only lightly buoyant, would make a fine solution. Embed a ring on the top to tie them together or tow them around. - Jesrad
Some info from Jesrad so it doesn't get buried in the forums.
Wed, 06/04/2008 - 15:25 — Jesrad Abrasion still wins However strong the bag, it will eventually wear out from abrasion because of the sand, which is much harder than plastic, and waves bending the bags continually even if only slightly. And then the mud would dissolve away through the holes. For this reason, using some viscous and buoyant oil might be beneficial if it is cheap enough: it won't wear out the bag from constant wave action, yet provide the same benefit as breakwater. For better wave stopping power you want the most rigidity over the most depth: wave energy travels by being spread over a half-wavelength down from the surface, the more you catch of it the less the wave penetrates.
Another solution would be to pack the sand so it won't move, maybe even making it wet, then tie to those some bags with just air in them for the buoyancy. But then you get a more complicated design with more potential failure points. Also, using few very long tubes is more risky than using more shorter tubes, for any failure in one would be less serious.
Another thing that might weaken the bags, is ultraviolet light from the Sun.
Stacking the tubes horizontally solves the loss of buoyancy with depth, but it makes the tubes harder to stuff in the first place because the air inside would need to be pressurized. Or you may reuse Richie Sowa's cheap pressurization technique for bottles, consisting of adding some carbonic ice inside before submerging them.
Overall, I think it's still a great idea that might be adapted, and maybe eventually be used for land making directly. The bags might be good substitutes for the plastic bottles nets and bamboo platforms of Spiral Island. Maybe covering them with nets, then tieing the inhabitable structure to that net, could be workable and stable enough, if the bags have enough mass.
- What about making two kinds of bags, half of them filled with air and the other with sand, and packing everything together with ropes, so nothing can move? Joep 19:36, 4 June 2008 (UTC)
- Two kinds of bags tied together introduces a failure point at the rope: if it bursts the buoyancy is seperated from the mass. What about the "Habakkuk" method ? Have a hose circle around the seastead, circulate a coolant inside to freeze the water and make a floating breakwater out of ice. By adding dust to the mix, it can be made extremely solid and more resistant to melting. Or make the hose circulate inside a plastic tube of seawater, but then it might burst from expansion when it freezes. Or make the tube out of bubble wrap so it compresses, and helps with thermal isolation so you need less power to maintain the ice ring. - Jesrad