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Building materials for seasteads

The high seas are (theoretically) open and free, but come with many construction challenges. Waves and winds should be familiar to all of us. I'm going to talk about construction materials options in the presence of the unholy trinity of biofouling, chloride corrosion, and UV.

Aluminium. Lightweight, inexpensive, easily recycled, handles UV well. Moderate difficulty to work and to repair. No particular resistance to biofouling if left in contact with water, but is not vulnerable to burrowing. Is destroyed very quickly by chloride corrosion. Not a practical option unless you are in a low-chloride environment like the Great Lakes of North America.

Cupronickel (including gunmetal, admiralty brass and similar). Moderately easily worked and recycled. Heavy. Invulnerable to UV. Extreme resistance to biofouling (toxic to invertebrates but not mammals or plants). Decent strength in tension compression and shear. Decent creep resistance. Horribly expensive. Resistant but not immune to chloride attack - no crevice corrosion or pitting, but sheds material very slowly across its entire surface. Combined with its cost this is like watching banknotes blow over the side. Can be practical for piping and similar when too small or inaccessible for inspection and maintainence.

Polymers (plastics). Lightweight, inexpensive. Uniquely vulnerable to UV, this can be managed with coatings, free-radical stabilisers and UV-absorbent fillers such as titanium dioxide. Mostly low strength, lower stiffness and no creep resistance unless reinforced with glass fibre, carbon fibre, or metal fibre. Easily recycled... unless you add fillers or reinforcement: you need both. Good resistance to biofouling. Essentially immune to chloride attack (though metal fittings and reinforcement might be vulnerable). Cheap and practical to build, moderately easy to repair, impossible to recycle.

Steel, coated. Very easily worked and repaired, moderately easily recycled. Cheap. Moderately heavy. Immune to UV. Coating can provide good resistance to biofouling. Excellent strength in tension, compression and shear. Excellent creep resistance. Quite vulnerable to chloride corrosion and related sulphate corrosion, can be managed with constant inspection and maintainance. Best option for working boats / infrastructure that expect to be damaged and repaired almost constantly.

Steel, stainless 316. Easily worked and repaired, moderately easily recycled. Expensive. Moderately heavy. Immune to UV, highly resistant to biofouling, more so if coated. Excellent strength in tension, compression and shear. Excellent creep resistance. Resistant to chloride and sulphate corrosion, doubly so if coated. This is not true of the cheaper 304 stainless and similar. Best all-rounder if you can afford it.

Your thoughts? Other options I may have overlooked?

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Discussion

𝔼𝕣𝕪𝕟 𝔹𝕣𝕒𝕔𝕔𝕠 2y ago

I’m not an engineer but I do have thoughts on designs.

Most seastead concepts I’ve seen are some kind of futuristic city. I think liberty is better served by customizable, attachable / detachable crafts capable of supporting a small group like a family.

If you like a community, bring your home over. If things go south, you can head out.

Depending on your particular industries, slip in or create modules for farming, aquaculture, manufacturing, etc. keeping the option to specialize or generalize.

Low Information Voter 2y ago

I think this too. Congregate like fish in particular locations for particular reasons, but keep option of moving on.

mark tyler 2y ago

Maybe they could have connectors that generate electricity from passing waves too.. though solar + storage may more economical than waves + storage.

Low Information Voter 2y ago

Practical Wave power is something of a Holy Grail in alternative energy. Friction, biofouling and corrosion have defeated every champion so far.

But storage is a Hard Problem, too, especially at scale. An old colleague is now working with flywheel storage, which is very exciting, but not something I'd try to use at sea!

Wave power is not locked to daylight hours, even very marginally-economic wave generation could be attractive for a seastead even if nowhere else.

The Beave 2y ago

316 is not great for structural stuff. Skinning? Sure. I would not rant to try to design a while ocean going vessel relying on 316 to withstand the rigors of years of being pounded on. IIRC, it's also going to work harden. If I'm correct about that, you will be chasing cracks that will continually propogate and there's nothing you can do about it except possibly heat treat the entire structure, and that is not practical.

More (exponentially more) expensive but the "best" metal would probably be Ti. But, this would be lighter than steels, more corrosion resistant than most stainless, might be prone to work hardening, but alloying and proper design can mitigate most of that concern.

Low Information Voter 2y ago

316 is used commercially for tanks in ocean-going product tankers, its not THAT bad! But sure, maybe restrict it to skinning.

My other concern with 316 in a seastead is hydrogen embrittlement when around batteries with aqueous electrolytes.

Probably shouldn't have said "best all-rounder" :-p that was asking for trouble.

(But it is! :-p Just not best at everything).

The Beave 2y ago

Tanks inside aren't subject to as much stress as the hull of a ship, since they are usually made to be pressurized or work in tension. With stainless you have to be a lot more careful of temperature gradients placing stress on joints/fastening.

I'm just not a fan of stainless as structural parts. I weld enough stainless used in various safety related systems to just hate it. Customers wonder why the parts come out so funky, when they are requiring at least 5x too much weld on pieces and don't understand that stainless warps way more than carbon steels. I think you could make it work, though, but it would require better engineers than I'm used to working with to pull it off.

Proper venting would reduce/eliminate any hydrogen concerns, especially if you double or triple seal the batteries, or use sealed batteries for a majority of your power storage.

Low Information Voter 2y ago

LOL true, re stainless.

Re batteries, you are correct, but sadly a seastead isn't subject to military or even commercial discipline. Some bored teenager or suburban dad is going to remove / disable the fan or barrier features, and embrittlement is nontrivial to pick up. We need not just idiot proof but owner-proof

The Beave 2y ago

Oh. You're talking about building stuff for other people. Eff that. I'm a pretty seriously competent idiot, but I know they make industrisl trade idiots that put me to shame. I would not want to try to design and build something so complicated as a seastead and then let other people try to not break it.

If they sign a contract and end up with a cracked hull because they didn't do the thing they were supposed to do, that is not your fault.

Low Information Voter 2y ago

ROFL

In a seastead, they're probably moored to my vessel and several more. And while I'd like to cut them loose and let them sink, Murphy's Law says the guy who does this will be the nephew of the Secretary of the Navy and the only reason we've not been blown up yet as a "hazard to navigation" :-D

The Beave 2y ago

Meeeeh. Fine.

Use as many passively redundant systems as possible, coupled with stupidly redundant fail over monitoring. My brain hurts thinking about the wiring system just for that alone. I'd rather build a car from scratch... LOL

Low Information Voter 2y ago

Ti would be best, even if scary-expensive, but AFAIK its nontrivial to work with. My old boss once dated a Russian academic who had worked on processing Ti for their submarines. I never learned any of the secrets, but apparently the forces involved in pressing it were very hard to reproduce without billions in budget

The Beave 2y ago

Eh, yes, but, no?

The Ti forgings for the SR-71 required building the world's most powerful presses. Two were made. Only one still kind of exists, IIRC.

If you're trying to do that kind of thing, yes, you need boatloads (literally) of Fiat. However, you're not building a pressure vessel. You are building a floating structure. You can do most of the work with formed sheet metal. Welding Ti is totally achievable with fairly standard practices, just with more shielding with either trailing cups and backing or various other methods used in aerospace. It's hard, but 100% doable, if you can get the material. China is pumping out millions of cheap Ti goods formed to a very precise degree. (I have a Ti flask that is comically light.) The tech is there, and achievable.

Low Information Voter 2y ago

I'm sold

We're going to need more Zaps :-p

The Beave 2y ago

And yet, you don't have a wallet set up... WTF?!

Low Information Voter 2y ago

I'm a monster... I was going to setup my own LN node, but got called away and haven't gone back to it.

Okay, where would you recommend for hosted wallets?

The Beave 2y ago

Pfft. I'm a newb. WoS works, and I'm not planning to use the sats I'm zapped for anything but zapping, so I don't care about phone nodes or others.

Luke 2y ago

I just use an Alby wallet here on my desktop. Works great.

Stacking Functions 2y ago

I’m not seeing the Kon Tiki option lol. I do appreciate this write up though

Luke 2y ago

I've heard that Titanium is still too expensive at our scale, but a particular grade of aluminum is what a lot of oil rig pontoons are made of. Oddly, when I look around online now, industry standards say 316 Steel everywhere I look.

Either way, do you know if the thermal spray coatings they do with molten zinc or zinc/aluminium alloys work on both steel & aluminum? Sounds like those are needed for longevity in both cases.

Low Information Voter 2y ago

Molten zinc spray will melt our aluminium, I expect. Maybe not literally, but enough to make it sag and creep under load. Steel would be fine, but need it sandblasted and perfectly dry for adhesion. So while this may be possible in manufacturing on land, its not maintainable "in the field".

There are a lot of different paints and coatings we could use. I wouldn't attempt to choose just one, but its a mature industry with huge economies of scale and many niches.

Luke 2y ago

I can't think of any spar & framework material that is maintainable in the field except concrete. (Which has pro-reef properties underwater) Maybe the goal should be to use whatever metal framework is cheapest on the inside and cover it up completely in concrete? That way it could be patched in the field, and seastead platforms could last centuries.

I've also had the idea to make each spar completely detachable so that if it had a problem we could simply pull a pin and drop that one, depending on dozens or hundreds of other spars underneath the entire structure to absorb the load while a new one is being made/shipped out.

Low Information Voter 2y ago

With a caisson, anything that is weldable is field-maintainable these days. At least, carbon steel is, I have on good authority.

Concrete I am deeply conflicted about. Wire-reinforced concrete is the traditional material for oversized, under-capitalised "heartbreaker" projects that end marriages but never leave the building yard (except eventually to a landfill) :-p

Concrete has very good compressive strength and creep resistance. But is hopeless in tension and shear. The steel wire mesh upgrades "hopeless" to merely "poor". Until it rusts into powder and bursts the surrounding concrete as well. And it will - high pH concrete doesn't protect against chloride for long. Instead of steel reinforcement you might think to try using glass. But the high pH makes glass hydrolyse into gel. You can use stabilised glass with a high % of non-silica glasses, but there's no real advantage (cost or otherwise) over glass reinforced plastic then.

What concrete CAN do is something unique, and Luke I think you alluded to it with your "reef friendly" comment.

Biorock. Aka Seacrete.

If fully submerged in seawater, and if the reinforcing mesh is electrically conductive (metal or carbon fibre), and if a current is impressed on it (with the mesh as the negatively charged terminal), the concrete "grows" and "self-heals" with minerals from the seawater (mostly Brucite). Hard-shelled marine invertebrates colonise the surface and grow at amazing rates, using the electrical current to fix shell-building minerals more efficiently than they can in nature.

At least, that is what the patents and many articles tell us.

I plan on doing some experiments myself, starting this weekend.

For a permanently submerged module (or entire seastead), concrete could be amazing. I planned to do a proper writeup with links, but for now:

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

mark tyler 2y ago

Love this. We should commission a design for mass production and have ten thousand made