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In my magical world, for reasons magical, metals such as iron have never gotten used, and even use of bronze is scarce. On the other hand, magic allowed for refinement of wood, similar to the densified wood, although the material produced isn't as strong as the densified wood, but is still a lot stronger than regular treated wood used for 16-18th century ships.

Well, this leads to some problems that I need to address for my naval battle to feel realistic. Let me explain the situation. We have setting of civilizations, whose development outside of magical advantages is similar to 15th-17th century.

A large isolated empire has recently ended their isolation and sends one of their fleets of ships that are quite long (longest being 156 m long flagship, but other large ships being at least 100 m in length and core medium sized ships still being around 70 m long) but somewhat less armoured against a small island country. These ships have been built for battles that focus on archery and short ranged (<200 m range) fire magic. Recently, they've also developed magical cannons.

Most of their ships simply have 2-3 magic cannons in front, and only their flagship actually has almost broadside design with 12 magic cannons (magic cannons are hard to make, so they use 1 front facing cannon and 11 cannons on single side, with addition of forecastle and aftcastle for archers and magic flame throwing weapons).

Small island country they're attacking is behind on magic technology, but way ahead on naval cannon tactics, as they have started using magically-hardened-wooden black powder cannons and have been working on naval cannon ships for some 80 years by now. They have already developed ships of the line, and while their navy is small, with only some twenty large warships and thirty frigates, their ships are built to at least somewhat withstand their own atrillery.

Important advantage of a magical cannons for this scenarion is that it uses magic force transfer, rather than explosion, to propel the cannonball, and thus it can easily fire 38.5 pounds (18.5 kg) cannonballs (which, however, are made of granite[because no iron] and thus are size of the iron balls of 110 pounder), but it only has around 350-375 m/s muzzle velocity.

On the other hand, wooden cannons of the islanders fire 11 and 24 pound (granite) cannonballs (which are the size of 32 and 68 pounder calibre iron cannonballs) with 400-425 m/s muzzle velocity.

While I do have multiple other problems I need to solve for this battle, my current most important question is, how do I make sure whether these guns are good enough to substantially damage enemy ships, or taking in account magically hardened wood, are able to damage the ships at all?

Edit: Reason I didn't assign specific value to the wood hardness is because that is, sort of, what I am looking for. I need a way to decide how hard the wood should be for existence of cannons to still be reasonable. My goal is for hardened wood to be reasonably more resistant than wood, (equal to at least 2-3 times thickness of regularly non-magically treated wood for things like shield). If that is impossible, I might have to adjust cannons calibre to make it possible. I am looking for some general advice on how to approach this problem, or alternatively numbers for real life black powder cannons vs wood penetration, so that I have some framework to work with.

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    $\begingroup$ You could look into history as to what happened when the first metal-reinforced ships made their apparition against wooden ones (there was a transition phase where ships were wooden with only a protective outer shell of metal). $\endgroup$ – Echox Dec 16 '19 at 13:20
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    $\begingroup$ @FailusMaximus: It also points out that there were historical ships that could do this without magic. The U.S. Navy's original six ships were made of a very tough wood that wasn't available in Europe and the first in class U.S.S. Constitution was nicknamed "Old Iron Side" after engaging and sinking the HMS Guerriere, with very few shots from Guerriere hitting the ship and one cannon ball being observed by the crew to simply bounce off of her hull, rather than damage it, as if made of iron rather than wood. She is still commissioned, making her the oldest commissioned ship in the world. $\endgroup$ – hszmv Dec 16 '19 at 18:37
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    $\begingroup$ @FailusMaximus: The battle that earned that earned Constitution her nickname was during the opening days of the War of 1812. The first Ironclad ship was the C.S.S./U.S.S. Merrimack/ C.S.S. Virginia (What the ship should be called is up to who you ask. It was salvaged from the U.S.S. Merrimack but renamed the C.S.S. Virginia though the former name was popularly remembered thanks to her nemesis ship being the alliterative U.S.S. Monitor). $\endgroup$ – hszmv Dec 16 '19 at 18:42
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    $\begingroup$ If you hava a reason to not make the islanders' cannon balls magical as well (perhaps some property of the island, either the rock itself or the way they make the balls, either done on purpose or "accidentally" achieved by the islanders), you could edit it into the question. If you have no reason to not do it, then you have your solution to do exactly as much damage as you want right there: change the cannon ball. Maybe it dispels or supresses the magical hardness of the target it hits, for example. (I can turn this into an answer if you think it's worth it.) $\endgroup$ – hyde Dec 17 '19 at 15:54
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    $\begingroup$ without a knowing the strength of the magic wood the answer is pure opinion. $\endgroup$ – John Dec 17 '19 at 19:05
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There are 2 main ways for cannon shot to damage a ship's hull. The first is to make a hole in it, causing potential flooding as well as sending shrapnel into the interior of the ship.

Second is to not penetrate but cause enough of an impact that shrapnel gets dislodged on the inside of the hull anyway, and possibly connections between plates and other structural components getting dislodged or weakened.

So even if you get no hull penetration, the impact forces themselves can cause significant damage.

And don't think that the wood splinters are harmless the way those you get from sawing or using a chissel are. These are shards of wood moving at considerable speed and in sea battles between cannon armed ships (both wood and ironclads, and to a degree steel as well though the properties of steel mean there's less of a risk of them) can cause massive damage to equipment and people inside the ship. Many a ship's cannon deck ended up a slaughterhouse of mangled corpses from a few impacts of cannon balls, the crew mowed down at their positions by shards of wood 30-50cm long and moving at great speed, skewering them.

If you make the wood the consistency of iron plating, this can get even worse. Now turn the cannon shot from solid balls into the equivalent of a HESH type anti-tank shell, basically a thin metal shell filled with plastic explosives that gets plastered as a blob against a sheet of metal and explodes, expressly for creating that shrapnel effect and destroying the interior even if the hull isn't penetrated, and you've the perfect weapon for your age just as HESH was the perfect weapon for the 1950s when tank guns were becoming too large to fit tanks in order to be able for their solid shot to penetrate the ever thickening armour plating of other tanks.

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    $\begingroup$ HESH is not possible with the available technology. They used muzzleloaders specifically because they required an open flame/spark source to ignite gunpowder, they didn't have reliable contact fuses. And timed fuses relying on matchcord were notoriously inaccurate. Reliable contact fuses require mid-19th century technology (percussion cap) $\endgroup$ – vsz Dec 17 '19 at 5:43
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    $\begingroup$ @vsz if you have magic anyway, a magical explosive and fuze can no doubt be invented :) $\endgroup$ – jwenting Dec 17 '19 at 6:31
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This is your world.

If you decide that they are able to penetrate the ships armor at certain points of the hull, then they are able to do it.

Nobody but you knows how strong this magic wood is. (Also after a quick scan of the shared article I didn't see any numbers on hardness) Just stay consistent with what you establish.

If your magic wood can withstand a 24 pound cannonball in one chapter and bursts from some musketeer gunfire in the next, then it is a problem but other than that you can have it be as strong or weak as you like.

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  • $\begingroup$ Sorry, but this is not a kind of answer I am looking for, I need something more specific, however I am thankful, since you have helped me realize that my question didn't really make that obvious. I have now added edit to explain why this format of answer isn't what I'm looking for. $\endgroup$ – Failus Maximus Dec 16 '19 at 13:07
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    $\begingroup$ @FailusMaximus it's however the only realistic answer without knowing the exact physical properties of your magical wood. $\endgroup$ – jwenting Dec 17 '19 at 4:45
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Round shot/cannonballs may not be the best option.

If the ships in question are powered by sails, I would focus on bar/chain shot types (i.e. two smaller cannonballs joined together) since they are good at wrecking sails, masts, and rigging. Since most ships lack enough weapons for wide firing arcs, they become significantly compromised once their manoeuvrability is destroyed. It may be possible to design cannons that fire these projectiles more optimally than real life equivalents, helping to close the energy gap.

Alternatively, technology permitting, you could load sharper ammunition for better penetration at similar power (sabots are useful here). Because this results in smaller holes, you may want to heat the needles before firing them so they can set fire to the target (or, in the case of the islanders' ships, the target's gunpowder storage). Using hot ammo may require heavier stone cannons, and the less magically-adept faction may only have furnaces on shore batteries for safety reasons.

Then there's the obvious answer: magicbane shot. For self-evident reasons, this would be used exclusively by the islanders in stone or metal cannons. Basalt (the main rock of volcanic islands) includes large amounts of iron, which can be extracted in a bloomery furnace. I know you said iron isn't used much, but a common material that can break through magic defences is simply too good to not be used. (aside: a magic insulator or nullifier would also be extremely useful for putting magitech into practice. Think of our world: everything runs on electricity, but an insulating plastic is almost always the user-facing layer. By making iron antimagic, you are increasing its importance in a magical society, not decreasing it)

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    $\begingroup$ It is an incredibly common trope to use the idea that iron was harmful to witches in someway and also that it is immune to magical affects. For this setting, widespread use of iron without knowledge of metallurgy would actually be a very likely result. If anything, it might make iron a major export for the island nation because it is easily produced for them and nobody else really has any understanding of what it is or how to get it. This totally goes against the premise of the question, but I think it's a valid point to be made. $\endgroup$ – TitaniumTurtle Dec 16 '19 at 17:25
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This question immediatly made me think of the way hardness and solidity is treated in some tabletop rpg. Since you asked for specific values and scales to compare, you could use Pathfinder's tables, with some exemples of special materials, and for your information, a cannon. For exemple :

  • The cannon i've linked does arround 27 damages.
  • Normal wood have 5 Hardness and 10 HitPoints/in. of thickness. That means if the hull is 1 inch of thinckness. An average hit from the canon will do (27-5) 22 points of damage on the 10 hits points hull, destroying it.
  • Now if we pick "Steel, Living" from the special material page linked wich come from trees so i think it's ok, and we do the math again 15 Hardness and 35 HitPoints/in. of thickness : (27-15) = 12 points of damage on the 35 hits points hull. The hull is still standing with 23 HP (and still 15 Hardness), damaged but not to the point of breaking.

Theses rules are not meant to be perfect, for exemple, what size of the hull is damaged ? But I think they are relevant to your question.

That were only exemples, feel free to tweak the numbers of Hardness, Hit points, inch of thickness and damage af you cannons and compare them to existing materials and there description

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  • $\begingroup$ While this isn't what I need right now for this question, it is going to be extremely helpful once I'm actually trying to play out the ship battle. Thank you. $\endgroup$ – Failus Maximus Dec 16 '19 at 21:52
  • $\begingroup$ I'm glad to help, i think it could be useful to you right now, to kind of reverse-engineering your hardened-wood and wooden-cannon. Start with what you want : "make sure whether these guns are good enough to substantially damage enemy ships". And play with the numbers to reach that goal, add special properties maybe (vulnerability to fire or iron as other answers suggested). Compare with given exemples of materials to know how to describe yours. If it's good for your storie, keep it, otherwise continue. $\endgroup$ – some_random_dude Dec 17 '19 at 3:29
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If this information is crucial to your writing, ultimately, nothing we do here can prevent you from having to decide on this particular wood's modulus of rupture - you are going to have to design your wood backwards based on the desired effects of your islander's cannon fire.

That being said, I will offer that you may be overthinking this. Building a wooden ship keel is already a difficult, expensive task for skilled laborers and masters of the craft. In your world it now also involves magic, and the cost of those magics is largely in your hands. If cannon fire is still a valid concern in naval combat, perhaps it's because the hull of the ship is far too expensive to treat in this manner.

I would also remind you that regardless of how many holes you can poke through the hull, unless you can hit below the water line and penetrate, the holes themselves matter relatively little. Classical cannons-at-sea combat favors tearing apart the enemy's rigging and sails, because cannon fire is near useless when the ship cannot be turned.

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  • $\begingroup$ Problem is that magic is weak but widespread (everyone has magic, although there are five diferent kinds of users depending on their talents), and material working magic (called shaping, ability to shape and refine "living" materials) is the most common talent. While refining wood is skill dependant work comparable to metalwork, one of big things is ability to connect wood, as if it was always one piece. This means that shipbuilding isn't harder than in our world and certainly not more expensive. $\endgroup$ – Failus Maximus Dec 16 '19 at 15:40
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    $\begingroup$ @FailusMaximus, then unfortunately you've placed yourself in category 1 - if it really is important, then it's time to do the math. The number you need to engineer is called 'modulus of rupture', and you'll need to generate estimates based on the expected output of those cannons. Frankly, I think you'll find that ironsides-class vessels already wouldn't have much worried about your islander's cannons, and adding magic makes the islander cannons of no consequence. $\endgroup$ – Sean Boddy Dec 16 '19 at 16:00
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Put the numbers down and walk away with your hands up

You've gone too far down the rabbit hole, none of this will really help you.

What's going to help is knowing that they're using magic wood on their hull. With normal wood the cannon become effective when you can make out the uniforms of the officers on board with the naked eye. With magic wood the cannon only become effective when you can also see their ranks.

Don't give fixed numbers, especially not muzzle velocity and material strengths. These require a significant technological base to measure and understand. Give human values, distances at which you can see something, like the whites of their eyes (accurate musket range). Your cannon will work, you define them as working, all you have to do is give the range at which they become effective in an emotive way.

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