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I have an empire set in a medieval era tech level. It has to have a powerful navy to defend its shores from pirates (it controls the entire continent) and it has a problem: lack of wood. The wood is hard to get because for thousands of years it has been used to build hovels and now it is in such scarce supply that it is impractical to use. What qualities would a substance have to have that would make it:

  • practical for use in warship construction

  • impractical for use in housing(e.g. Hovel construction)

The pirates are from another continent that is sparsely populated and cold (think a giant Scandinavia) and is unconquerable due to the war-heavy natives. Efforts have been made to establish colonies, but since the 'Vikings' are so good at navigating water ways they have overrun any and all colonies. Also, these 'Vikings' are not interested in trade, only plunder. This makes wood impractical for the Empire due to the cost of sending a large army overseas, supplying this force, and then dealing with unpredictable native kingdoms following a warlike religion. All the while a navy is required from the get-go for this to be a possibility.

To clarify, I am looking for the qualities of such a material, not real world alternatives to wood. I am going to design a new material based off of the qualities given to me by the correct answer.

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  • $\begingroup$ “You wish to sail a ship up stream by lighting a fire under its decks, I have no time for such nonsense.” ― Napoléon Bonaparte. Ironclads will work, but they function best in shallows and on rivers. Are these warships intended for ocean sailing, or is it a relatively shallow waters that they are needed for? $\endgroup$ – Twelfth Feb 27 '15 at 21:38
  • $\begingroup$ @Twelfth Ironclads are iron-clad, which means they're really metal-plated wooden ships. Also, just because america only had ironclad monitors doesn't mean the first-rate navies of the day couldn't do better, viz. HMS Warrior or Gloire. $\endgroup$ – Mike L. Feb 27 '15 at 21:41
  • $\begingroup$ The US also had an ocean going Ironclad ship like the Warrior in the ACW: the New Ironsides. The city class river ships were casemated too. $\endgroup$ – Oldcat Feb 28 '15 at 1:28
  • $\begingroup$ Wood is by definition a renewable resource. Just how does building hovels use up the wood supply? $\endgroup$ – Oldcat Feb 28 '15 at 1:30
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    $\begingroup$ This is silly. All historical empires had lands designated as royal preserves (the word "paradise" comes from the Persian version of the term), some specifically for the type of wood (such as Lebanese Cedar) needed for shipbuilding. $\endgroup$ – Serban Tanasa Feb 28 '15 at 17:07

13 Answers 13

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If you're limited to historically accurate mediaeval tech level and wood is too expensive for even your Empire to afford, you're not going to be building very many ships. The best option for you, if you insist on having a navy, is to bootstrap a navy through alternative means and get your wood in counter-raids from the pirate lands.

Because you tagged this "medieval", I'll be thinking in terms of galleys and combat based primarily on boarding actions. Actually, it turns out that you'll be wanting to do that anyway, because the best seaworthy ships you're likely to get your hands on are the ones used by the pirates.

What you should probably be thinking about are boats rather than ships. Without significant technological advances, you won't even get close to producing the amount of steel you'd need for steel hulls (not to mention binding it all together), but you can use alternative materials to build some boats that probably won't topple over if the weather is favourable.

Material options

Your first option is bamboo, or a similar plant. Though you can technically build a hovel out of it, it's not something you'd want to spend a winter in; on the other hand, larger diameter bamboo trunks will float, so you can use them to make a boat that will accomodate a couple of soldiers. If you have bamboo, it will also make a half-decent mast material (if you cut and bind it right to keep it from flexing too much).

Another option that comes to mind is rubber. Though producing it would require you to have the right kind of trees, you don't need to fell them to make something out of the rubber, and since the original vulcanization process was discovered mostly by trial and error, you don't need to know much chemistry either. Vulcanize some rubber with sulphur and have someone blow into it through a glass tube to get some air bubbles inside; this should get you a batch of rubber foam that should float (for a while). Playing around with molds could again let you make a boat that's good enough for near-shore boarding.

If you have the right kind of volcano on your island, you could find pumice deposits somewhere. Pumice is a highly porous rock that's actually less dense than water, so you could conceivably fashion boats out of it, but they're going to be less than seaworthy. Construction-wise, it's stone, so yes, people could use it in construction, but that goes for any other stone as well, and I'll go ahead and assume your empire is not entirely devoid of that.

Finally, and this starts smelling a bit like fantasy now, you could try developing fiberglass. If you can make glass wool (difficult, but not inconcievable) and if you happen to have some sort of resin that you can either directly use as, or refine into, a coating and binding agent, you can try producing fiberglass that will be brittle, but reasonably watertight and good enough to make small boats out of. Again, this is leaning towards fantasy now and requires some development in "alchemy", but with some author intervention, the ingredients are there.

What do I do with all these bloody boats?

Why, you board and capture attacking pirate ships, of course. Hopefully your soldier's lives are cheaper than wood would be, so you can throw however many you feel like at attacking incoming pirates and just keep their ships for future use (prize warfare - capturing enemy ships for your own use - was a thing well into the 19th century). As long as they keep coming, you're building up a navy (and if they decide to stop coming, you no longer need one anyway).

When your navy is sufficiently built up, you load your ships with troops and lumberjacks, and organize an expedition into the pirate lands. You don't have to stay long, so as not to give the natives too much of an opportunity to attack, just long enough to get a few shiploads of (probably extremely expensive) wood.

You ship this wood home and sell some of it for exorbitant sums to help finance your shipbuilding industry. Congratulations, you have now sucesfully started importing wood, and can continue doing so for as long as you like.

You have a choice of keeping up the raids, or trying to establish more permanent outposts to fell timber. Even given the risks involved, if wood was originally too precious to build ships out of, there will be an extremely powerful economical incentive to establish these; this should help you obtain both financing, and willing mercenaries as guards.

Either way, you should by now have enough of a navy to be able to at least organize convoys to protect the wood shipments, which will be further protected by the fact that their precious cargo is not precious to your pirates at all; after all, why would they risk their lives to steal something that literally grows on trees in their homeland.


EDIT: Well, unfortunately the question changed rather significantly while I was writing my answer (also, it no longer matches its own title). The thing is, any material you can build seagoing ships out of can also be used in housing construction; after all, you can always overturn the hull and live inside. You could get around the problem by using a combination of materials, of which one would be structural and one would float (so that you have no single material that's both load-bearing and insulating); something like the rubber foam or pumice I mentioned above, but like I said, neither of those is something you'd really build a ship out of.

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  • $\begingroup$ Fiberglass is feasible but not steel? Come on man, fiberglass was a 20th century invention. If you've got resin to bind it then just use wool or another natural fiber. Either way, I'll ram you with my steel ships because my blacksmiths figured out have to make plates. $\endgroup$ – Samuel Feb 27 '15 at 22:07
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    $\begingroup$ @Samuel Yeah, fiberglass is a bit out there, though the biggest problem there is the resin, which can just happen to occur naturally if you're lucky. I still maintain that no steel-hulled ships you could make with available technology would stay afloat. $\endgroup$ – Mike L. Feb 27 '15 at 22:12
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You might try ferrocement shipbuilding. If steel is not to be found in your empire yet (remember that steel furnaces as tall as two store buildings already existed in China during medieval times), you might try bamboo as load bearing material.

For ferrocement to work you need a steel mesh core and a cement as stuffing element. Its not much dissimilar to how composites work, but instead using steel as "fiber" (not exactly a fiber) and cement as resin (not exactly a resin either).

Steel resists tensile forces very well, while cement resists compression.

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First, as somebody mentioned you do not need a fleet to defend against raids. If you have no wood to build ships you will not have large fishing fleets or merchant ships to protect. Lack of trade fleets will also limit the growth of large and rich coastal cities that would attract plunderers. Fortify the cities and villages against casual raiding (probably just keeps to protect valuables and for people to evacuate to), build watch towers along the coast and have garrisons of mounted archers at strategic locations for fast response. The pirates will probably focus on raiding each other.

Further any structural material that can be used to build a boat can be used to make a house. One structure that keeps the weather and water out is pretty much like another. Barring magic the requirements are simply too similar.

There are practical alternatives to wood though.

Leather. The Celts built leather boats capable of crossing the Atlantic. Treating the leather with lanolin (wool oil) makes it water resistant apparently. You'll still need some structural supports but the amount of wood needed would be vastly reduced. There might be animals with bones suitable for structural members. This is suitable for cultures that have lots of sheep or cows.

Reeds. Reed boats are also provably capable of crossing oceans. Suitable for cultures centered around rivers and lakes.

Stone. People do build ships and boats out of concrete and there are types of rock that float. Making a boat out of stone would be quite difficult and I don't think anyone has actually bothered, but there is no particular reason you couldn't. Other than the cost required for the expert masons that can fit the stones together well enough to be waterproof when treated with asphalt. Maybe a double hull with the space in between filled with asphalt mixed with something?

Cloth. Textile fibers could be treated to be water proof enough and even used to make "fake wood" for structures. It is hard to imagine a scenario where this would be cheaper than using wood. If you have no trees, you can always plant some and then tell some big men with pointy bits of metal to kill anyone who tries to steal your precious wood.

Probably ships would be build from a combination of those alternatives. Say, stone for rigid structures, bone for flexible structures, treated leather for the hull, cloth fibers to bind it all together and with asphalt to prevent leaks.

Actual concrete, glass, ceramics, or metal would pretty much require industrial production. And if your empire has no large forests or coal deposits they would have issues with the processes needed.

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Metal.

You can make warships out of metal plate if you don't have any wood. As long as it's water tight and displaces a volume of water equal to its own mass without water spilling over the top, it'll float. This makes it a well defended warship too. The main issue with metals will be corrosion, it'll need to be treated for long term use.

A Mississippi-class battleship uses a steel hull.

enter image description here

If it's too difficult to produce steel, cast-iron can be used. If the pirates don't have cannons then cast-iron will be ok, it's main disadvantage is it's brittle and vulnerable to direct shot. Concrete has the same disadvantage, but it also has poor flexural and tensile strength, so it would need additional reinforcement.

Obviously metal plates could also be used for home construction, but it's impracticality for hovels lies in the expense and expertise required to produce it. The king could also produce cheap homes from concrete, then use the wood for ship construction.


EDIT: You've now changed the question. You're asking for the properties of a replacement material and not a material. Perhaps your question title should not say "alternate materials". You might also include information like "we have almost no coal" and "there is no gunpowder for these warships" in your question description.

To make a ship to need a rigid material that can make watertight seals. Ideally it would be buoyant and fireproof. To satisfy the requirement of "impractical for use in housing" make it a poor insulator.

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  • $\begingroup$ Would a steel plate ship be practical for a Medieval ship? The world lacks almost any coal and no one has discovered gunpowder yet anyway, so how would one sink this ship? A few of these and they effectively not only protect their cities, but control the world seas and world trade. $\endgroup$ – JDSweetBeat Feb 27 '15 at 20:30
  • $\begingroup$ The metallurgy required to fashion steel (heck, any metal) plates for warship construction is 500+ years ahead of medieval technology. An empire that could churn out quality steel in such quantities could at the same time produce swords and armour that everyone else would call black magic. $\endgroup$ – Mike L. Feb 27 '15 at 20:40
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    $\begingroup$ @Samuel I'm not saying it's impossible to make steel, I'm saying it's impossible to make consistent-quality steel in such humongous quantities. With the crucible process you can make a steel ingot that you can make a sword out of, and if you judged everything right and have good ore, maybe it won't break. Making entire steel plates (and enough of those to build a warship) is a different world entirely. $\endgroup$ – Mike L. Feb 27 '15 at 20:44
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    $\begingroup$ @Samuel, steel production may have been going on for 4000 years, but the volume of production has been very low. The total steel production of Europe from prehistory through 1700 would not be sufficient to build the battleship Iowa. You'd be hard-pressed to find enough good-quality steel to build the Monitor, for that matter. $\endgroup$ – Mark Feb 28 '15 at 1:11
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    $\begingroup$ In fact, my main objection is not related to steel quantities but for the techniquest to work with it, specially for welding (as I stated in my previous post) that could resist even the weight of the ship. The bigger an object, the more strong the forces it has to stand, so the technologies that were enough for welding iron tools would not have been enough for welding a ship. $\endgroup$ – SJuan76 Feb 28 '15 at 16:52
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The tricky part of your question is that the material needs to be unsuitable for building structures on land. Well, I have a perfect material for you. It can be used to build a boat, it will be easy to come by for your Empire, and it is entirely unsuitable for the construction of dwellings on land. I'm going to suggest this material despite your question asking only for properties because it is so perfect. The answer is Pykrete! Pykrete is a mixture of water and wood pulp that when frozen becomes as strong as concrete and melts much slower than plain ice. It was invented during Workd War II and originally intended for ship construction! The Allies wanted to build an unsinkable aircraft carrier out of ice, but the project was scrapped. Despite its late invention it couldn't be more low tech! It doesn't even need wood pulp as the original formula calls for. Any plant fiber such as cotton or hemp will work. All your Empire would have to do is make the mixture and let it freeze. They could craft a mold, or chop it into blocks and construct the ship piece by piece, refreezing the blocks in place.

Of course, your ships would slowly melt. How long they would last would depend on the water temperature and thickness of the hull. They also likely won't be fast as the ships will need to be large and sail power isn't the strongest. Even with those caveats I think Pykrete represents the best (and certainly most interesting) option for your Empire's ship building endeavors.

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The big problem here is something you can build a ship out of but not a house. Dan Smolinske suggested something that has to remain wet--a working answer but we don't have such a material.

Thus, instead, I suggest combining two of the answers above.

Pumice floats but it's not strong enough for shipbuilding. Rubber won't make a house because it can't stand up. Rubber bubbles were suggested but they're prone to popping. Ok, lets make the basis of our "ship" be a big raft made out of a sheet of rubber full of pumice chunks. (Line a mold with rubber sheets. Fill it with pumice chunks, pour rubber in. Since it's full they have no place to float, they stay mixed in.)

Such a ship can't support a conventional mast but you could sail by means of kites. Since this is basically a raft it can't handle rough seas without waves continually breaking across the surface--it's not going to be a pleasant ride!

It does have one advantage for pirate-hunting, though--it's very low profile means that if you can get in front of a pirate you spread seaweed across the ship and they aren't going to notice you until they're almost on top of you and maybe not even then.

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What're the pirates using? I'm going to assume wood.

Capture (by money or force) one of their vessels, set sail (with bayonet at their throats) to the wooded isle, and bring back more wood / set up a naval base there.

Otherwise (at low tech, like your other questions are) you're looking at concrete. You'll still need wood for your masts.

An Empire can totally afford wood. You just set it off in a special preserve. That's what armies to guard it from thieving peasants are for. And peasants to provide the tax income to make it feasible to pay the guards.

If your Empire can't afford to have special forests for its naval construction (like Britain), it's not much of an Empire.

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    $\begingroup$ The pirates are from another continent that is sparsely populated and cold (think a giant Scandinavia) and is unconquerable due to the war-heavy natives. Efforts have been made to establish colonies, but since the 'Vikings' are so good at navigating water ways they have overrun any and all colonies. $\endgroup$ – JDSweetBeat Feb 27 '15 at 20:18
  • $\begingroup$ Probably should have mentioned in the question :) $\endgroup$ – JDSweetBeat Feb 27 '15 at 20:23
  • $\begingroup$ So, you go there to steal wood. Build ships, re-iterate. If it's sparsely populated they can't mount a coastal defense. You don't need their best wood, just some wood until you can grow your own. $\endgroup$ – user3082 Feb 27 '15 at 21:19
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The most obvious answer is that portions of it have to remain wet at all times.

Realistically that makes it unusable for housing, although it could be used on rivers or near the sea. Maybe a type of seawater plant with a rigid structure that you make the ship out of - keeping it alive - but when it dies and dries out, it crumbles and becomes useless?

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If you don't have resources to build a navy ships, you don't build them.

Instead, you build defense from pirate raids. Defend your river deltas with fortresses. Defend your beaches with walls, with pikes and build network of roads and observation points to quickly move your armies where needed.

And if pirates try to establish settlements on your land, attack them and take over their ships.

Whole point of war is not to fight strong point of your enemy by using your weak weapons, but to attack enemy weakness using your strength, or force him to fight where you have advantage.

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Your empire can always do what England and France did on several occasions: hire Pirates to defend your Empire from Pirates. It worked out OK for France with the Normans (they became troublesome when they were French), not so well for the English with the Saxons and Danes.

The issue for England at that time was that they didn't have any sort of land army either - so the protectors could turn invader with impunity.

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I don't know if it's available in your version of medieval tech*, but concrete works as a shipbuilding material. The US built concrete ships in WWI and WW2 (the remains of one can be seen here: http://www.parks.ca.gov/?page_id=543 ) You'd probably have to use an alternate reinforcing material, though. Also, many US universities participate in the Concrete Canoe competition: http://www.asce.org/concrete_canoe/

*The Romans had concrete. A good many of their concrete structures are still standing today.

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  • $\begingroup$ Late to the party :) $\endgroup$ – user3082 Feb 28 '15 at 8:35
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It should be worth mentioning Pykrete as a viable building material as well that would be easily manufacturer with that level of technology.

Basically, for those of you who don't know what Pykrete is, it's ice. Ice mixed with wood pulp. It was considered for real projects back in WWII and was even confirmed by Mythbusters (which makes it true :P)

Although it would still require the use of some wood, it would not be nearly as much as an all wood construction.

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  • $\begingroup$ The Mythbusters built and tested a pycrete boat in Alaska. This is medieval tech we're talking about, so unless the Empire posesses sub-polar territories, they'll only have a navy in wintertime. $\endgroup$ – Mike L. Feb 28 '15 at 15:59
  • $\begingroup$ One of the advantages of pykrete over just ice was that it was actually a slower melting substance as well. So yes, still temporary in terms of tech, but yes, if there were "Northerners" who could quickly and cheply build a rather large ship and then.. abandon in? like an aircraft carrier for smaller ships for the longer part of the journey. Just a thought $\endgroup$ – Get-HomeByFiveOClock Feb 28 '15 at 16:07
  • $\begingroup$ For a pykrete ship to last it needs a freezer on board. That's going to be hard to provide with midieval tech. $\endgroup$ – Loren Pechtel Feb 28 '15 at 18:44
  • $\begingroup$ It doesn't have to last, make them temporary. It's not like they cost very much and you can cannibalize all the non-ice materials like masts and sails. $\endgroup$ – Mike Nichols Mar 1 '15 at 0:50
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Assuming there is some genius who understands displacement, it is quite [possible to build ships out of concrete. (This is a pastime that some university engineering students indulge in).

A concrete ship wold be relatively inexpensive, certainly immune to most medieval weapons like bows and small catapults (large catapults on shore might be a different matter, but they would have to hit the ship first), and could be built with a board beam to make it a relatively stable boarding platform (the may many sea battles were fought in the Middle Ages).

I'm not clear why the material should not be used to build housing, but if the local rulers are keen to make a navy out of concrete boats, then the demand for concrete will be quite high and therefore the cost should also make concrete unaffordable for most other purposes (especially with medieval levels of technology to produce concrete). Shipyards will probably have plenty of concrete structures poured from the leftover batches of concrete mixed for ship production, with concrete being a rare and expensive material farther inland (maybe the local Duke builds his castle out of concrete, but no one else in the province).

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  • $\begingroup$ Late to the party :) $\endgroup$ – user3082 Mar 1 '15 at 10:52

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