Frogger needs help designing a bow

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Frogger5
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Frogger needs help designing a bow

Post by Frogger5 »

hey all! :D

I need help designing a ballista that fires "canonballs" (bear with me). It's for a story that I am considering publishing. The idea is that this ballista would be used for mid to late medieval warfare by a magical race. The race in question has fantastic bow technology and therefore when they decide to confront their enemy by ships, they design a giant bow for firing round projectiles capable of destroying enemy ships. Seeing as these people are completely inexperienced at designing larger than conventional bows, the design needs to be somewhat amateurish, but they have a decent understanding of physics so they know the basics.
Here is what I have so far:

http://www.servimg.com/image_preview.ph ... u=13308535

The thing is, I don't have the amount of understanding of physics and such as these people do, which is where I need help from anyone on this forum who can give it.

The main points are:
• It needs to be practical and simple to use.
• The design needs to be simple and reliable (the people is question are big on reliability).
• It needs to be capable of destroying a ship made of relatively brittle wood.
• I also need to know the ideal characteristics of the metal (or rock) used.
• The wood used can be virtually unsnap-able.

Before you post links for medieval ballista design references, this race is almost completely isolated from Europe.
Last edited by Frogger5 on December 18th, 2010, 7:39 am, edited 1 time in total.
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Velensk
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Re: Frogger needs help designing a ballista

Post by Velensk »

I havn't looked this up recently but I'm pretty sure that the Da Vinci ballista design was supposed to throw cannonballs. Try looking it up.

EDIT: Incidentally, I'm not sure what your problem with links to medieval ballista would be. If you want a large stone throwing device that uses crossbow-esk principles then it will most likely look/work remarkably alike other devices that operate under crossbow-esk principles regardless of who designs it. If it does not throw things with those principles then the device you are looking for is probably not a ballista.
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Frogger5
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

Really? Ok I'l have a look.

Hmmm :hmm: yes I suppose your right. I guess ill simply stick with a ballista and say that the reason they chose a ballista, and not say, a catapult, is because of their outstanding bow technology. I certainly can't use firepower, because they don't even know it exists.
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Re: Frogger needs help designing a ballista

Post by Jetrel »

Shipborne ballistae are not fantasy; they were a mainstay of most ancient naval combat. Egyptians, greeks, romans, and carthaginians regularly fielded them. Hell, the byzantines, during their later years (800-1400, iirc) were famous for having flamethrowers.


Quite a few traditional ballistae shot rocks, instead of shafts. The design is virtually identical; just a larger sling and track to accommodate a larger shot. Same thing happened with crossbows; late crossbows basically shot musket balls or small stones, and were called "stonebows"/"slurbows" (sometimes interchangeable with "arbalest"). They had become so powerful that the projectile didn't need to be pointed to do damage. And remember: anything that shoots rocks can trivially shoot metal balls. You just put a metal ball in instead of a rock. People just tended to use rocks early on (in both tension and gunpowder based weapons), because rocks are cheap, and aerodynamics didn't matter until distant ballistics came into play (also powder-based weapons had a potential to shatter rock projectiles on firing; not a problem if you're shooting grapeshot, but bad if you're intent on a single, powerful slug).


Anyways, if you're looking to damage ships, a cannonball sliced in halves, with both halves connected by a chain, is a great way to slash sails and potentially snap masts. Sinking ships is done with heavier shots (e.g. optimized for penetrating momentum), aimed at the sides of the ship near the waterline. Sinking metal ships is trivial, sinking wooden ships is considerably harder, since they're much more buoyant. If they're well-loaded (which many, many ships were; any ship planning on a long voyage), they'll go down, but if they're not filled with goods in the hold, the raw material of the ship might have enough buoyancy not to sink even if it's full of water. As a result, what a lot of pre-modern naval combat ended with was not sunken ships, but merely "listing" ships that refused to sink.

Gunpowder kinda changed the game, because explosive shells could actually blow a ship -apart-, and/or ignite stuff on the vessel.
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

The ships used, are merchant ships equipped for war. So therefore what you said about buoyancy could work ie: the merchant ships were build to contain large amounts of goods, so that when they are loaded with only four ballistae and rock and metal projectiles, they would float much better and move faster.

As for the alternate projectile used for slashing sails and taking down masts, I think I could use that, in fact that could be an advantage against the opposition. However instead of using a chain, I'd be inclined to have them use a strong rope, simply because they don't have the time to make chains, and the metal is needed for armor.

The fantasy aspect is that the projectiles are coated in a mixture of say, some tree sap from a magical tree, with symbols of fire carved onto it, so that they could fire flaming projectiles. This would be ideal because the western goblins (that make up the majority of the enemies they will be fighting)
are frightened of bright light and are used to living in the caves and therefore arent used to it, and also because as well as the wood the baddies used to build their ships being brittle (cus their soil sucks) it would also be somewhat flammable.

Rocks would be fine to use. Not only is there a good supply, but they have even more magical qualities of their own, and could produce even brighter and whiter fire. That gives me an idea. Take a bunch of sharp crystals, and put them inside a round blob of flammable and quick burning stuff (such as pitch) and set it on fire so that as it flies through the air the "pitch" burns leaving the sharp crystals to have a shrapnel effect on the enemy sailors.
This is really helping thanks :D
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Re: Frogger needs help designing a ballista

Post by Midnight_Carnival »

:lol2:
Great minds think alike!
I'd be inclined to have them use a strong rope, simply because they don't have the time to make chains, and the metal is needed for armor.
Firing from a balista I'd go for a spiky chain, with a canon they used chain shot thingies as Jetrel said. If you have a magical rope which could act like a carbon monofilament wire, your idea might make sense, but I doubt it would work well with an ordainary rope (no matter how strong).

Good luck writing your story, it's the details that kill.
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

Honestly, strength isn't a problem, making strong rope is child's play for them. It's more of making a rope that wont absorb the force when it hits the mast. Perhaps chains would be all right, as long as they used as few as possible.
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Re: Frogger needs help designing a ballista

Post by Dixie »

Also depends what kinda metals they might get their hands on. For instance, I could imagine lead being a pretty good material for solid, heavy mast-destroying chains, but very poor armor material due to its weigh. Likewise, I would imagine stuff like gold would be poor for both, silver too precious, and iron or steel better used on weapons and armors. Or any magical material of sorts you might have created.
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Frogger5
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

Ok, ill give a run down on the metals i have invented.

• Silvertope: A shiny silvery metal that is light with carbon like strength. Used for armour and swords. Plenty there, but has to be extracted from an ore like iron. Smooth and sharp, but very fine.

• Olsarin: A bright yellow, orange, golden looking substance that is thick, tough, blunt, and heavy. Used for reinforcing swords and armour. takes and enormous amount of heat to melt and therefore requires magical forging methods to be used. A wide range of powerful magical qualities. Considered too precious to waste.

• Unnamed: A black sort of half rock half metal substance, airy, light, harsh surface, slightly brittle, ideal for making clubs. Poisonous.

• Copper: Very rare on the continent, used for making coins.

Unnamed: A light cream colored rock, solid, dense, partially crystalized. Used for castles and such.

The opposition has no access to these materials, only real known metals, iron, silver and such.
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Re: Frogger needs help designing a ballista

Post by Zachron »

If I were the opposition, I'd take abundant copper and buy off the kingdom.
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Re: Frogger needs help designing a ballista

Post by Velensk »

Once you have paid the Dane-geld, you'll never get rid of the Dane.
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Frogger5
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

Zachron wrote:If I were the opposition, I'd take abundant copper and buy off the kingdom.
... nah can't be bothered correcting you.

Frankily I'm out of questions, unless someone else has something useful to say*, I'll be moving on to another topic I need help with.
*Everything helps.
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Re: Frogger needs help designing a ballista

Post by Zachron »

If their women are attractive enough I wouldn't care...

More on topic: I would picture a ballista of such massive size to be very simplistic indeed. Perhaps consist of 2 parallel springs, with the two strings intersecting at the basked where the ball is positioned. (Two bows, two strings. One string attached to the right end of the upper bow, and the left end of the lower bow, the other sting attached to the left end of the lower bow and the right end of the upper bow.) I picture the bows themselves being much like massive metal truck springs(If they have good bow technology, and metallurgy they probably use the bow spring for suspension on their larger wagons), about 30 meters across(length of the secant line between the two ends of a given bow not the actual linear lengths of the curved bars) about 1.5 meters tall, and about 6 centimeters thick. The strings would be high tensile strength lines splitting off three ways in a "Ψ" shape about 1.5 meters from each end, connecting to eyelets bolted through the top, middle, and bottom of each end of each bar. In the back of the bucket, where the lines all meet, a massive tow line pulls it back by a wince, which would require an ungodly amount of torque operate. (or perhaps a godly quantity thereof.) The tow line would be connected to the basket and the intersection point of the lines by a hinge pin, that is ever slightly conical, that it holds fast, but it pulls out with ease releasing the full fury of the weapon.

We're quite possibly talking tension forces on the order of Mega-Newtons here, which could send a ball of 20 kilos flying off at 500+ meters per second assuming the apparatus had a motion transfer efficiency of only 1%. Surely something within the realm of what a magical kingdom with it's exotic materials could accomplish. I'm assuming the metal bar would be composed of that "silvertrope" material you've described. The cables, the rings where the cables split and join, and the bolts which join the cables to the metal bar, would be made of that "Olsarin" material... not many of these great ballistae would exist.

A smaller version, made of wood, with more common metals forming the cables, would be more portable and thus more readily deployed in and offensive role. Picture it scaling down to 2 meters across, 5 meters across, 10 meters across, and 15 meters across being the largest ones aside from the great ballistae.

The properties of the stone balls largely irrelevant. All that is necessary is that the balls be dense, and thus be heavy. It would also help if they were inelastic(not prone to bounce off struff). Granite, is a good stone to use.

"Unnamed: A light cream colored rock, solid, dense, partially crystalized. Used for castles and such." <<--- What you describe there could be either marble, or white granite. Both are very strong stones. Granite is stronger and stouter, but marble keeps more of its strength when thinned down and is more elastic. As long as it's solid, and not bearing the infamous cracks that often move along it, marble is a good material to make fortresses with, but the expense of such would be massive. If the properties of pale granite and marble were combined in some sort of stone, some sort of "stout marble" it would be literally the ultimate fortress material, short of concrete. It would be a brittle material, although it does warrant notice that most all rocks(other than diamonds) are brittle.
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Frogger5
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Re: Frogger needs help designing a ballista

Post by Frogger5 »

To big. way too big. This is supposed to fit on the lower decks of ship. 2 meters across max. Not very big, but even still, I doubt it would be an issue seeing as the opposition's firepower is also relatively short range as well as their ships being made of low quality wood.

As for the projectile traveling speed, well, I can't quite figure that out just yet, but I'll probably get around to it.
Now in terms of actually drawing the thing. Well, its a tough wood with a lot of firepower. A body weight powered winch could work with a heavy duty ratchet. :hmm: My original idea was a hook that could be pulled by two people, but they'd probably do their backs.
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Re: Frogger needs help designing a ballista

Post by Zachron »

I guess you didn't read what I said about it could be scaled down to as small as 2 meters across. It could really be scaled down infinitely. Just Google search double crossbow. Also, A shipboard ballista could be 5 meters across, or even 10 if the ship was wide enough. The super ballista I described would have been tower bound.

As for projectile speed, there would be the average force over time, multiplied by the time the projectile is accelerated by the crossbow, divided by the mass of the projectile...or I could look at it in terms of energy. I gave a very rough estimate based on the assertion that relatively little energy is transferred to the ball itself. Mostly because my own knowledge of physics is limited, and I have not worked out a way to calculate precisely... Suffice it to say, projectile speeds are usually pretty fast. I merely delved into the bare minimum amount of physics to make it seem believable. Needless to say, God has killed many cat-girls on my behalf. 100 meters per second is more or less the average projectile speed leaving a long bow. 100-250 m/s for crossbows and ballistae, as far as I know. These yeilds are from wooden pieces. Search "truck spring crossbow" some time. (I would suggest searching bowflex ballista, but apparently the sort of people who actually buy bowflexes are devoid of creativity.)
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