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A long time ago I heard about a Medieval Irish pirate that used a Trebuchet mounted on his ship (no I am not sure what he was or where I heard it). The idea of a ship acting like a double pendulum when firing has always intrigued me and made me laugh. I am assuming that to prevent fouling with rigging it would have to be limited to broadsides with minimal adjustment. I envision it sitting between 2 masts midship.

What sort of design choices would an Age of Exploration Era European Vessel (capable of Atlantic crossing) make to avoid capsizing? Wider, deeper? I am pretty sure a long thin vessel would have an issue with capsizing.

What is a good rough counterbalance weight to ship weight ratio, and ship to ammunition ratio?

Traditionally trebuchets have longer range than mangonel or ballista, what sort ranges would a ship born trebuchet have? Similar to land based of comparable counterweight?

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    $\begingroup$ Naval artillery in general is firing lighter ammo than those needed in siege operations to break stone. If you are sending flammable balls of pitch you wouldn't need a large device to get some range. $\endgroup$ – Oldcat Dec 6 '14 at 0:53
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I'm not sure how safe it is to put a trebuchet on a ship. The main problem is probably the counter weight because it is so heavy. As you said, considering the size of a trebuchet (the mast is around 10m long)it's hard to conceive that someone would consider making frontal attack with this. Unless the ship is really long, they would break the mast or something. It might work with sideways attacks but you still need something to stabilize the ship. To improve stability, you could have a ship design multiple hulls, 2 or 3, next to one another.

My other concern is with accuracy. A normal trebuchet on land can fire maybe 3 or 4 times per hour with a well trained crew. On sea, the lack of space and movement of the waves make things more complicated. Not only it take a long time to fire but it's also not very accurate. It require ballistic calculation and a bit of luck. Humidity is a big factor influencing the projectile trajectory as it makes the wood and the ropes less rigid. And don't forget that you are on the water. The boat is always swinging especially when firing. Considering all of this, I have no idea of the range the ship would have but if you can fire it should be about the same. But if your enemy has some trireme (or a similar kind of boat), you won't even be able to fire once.

I am aware that the Romans did put catapults on their ships to attack Cartage but they lost the fleet in a storm and the ships where not really useful in combat anyway. Still, the catapult have the advantage that they do not require a counter weight. They are more compact and less likely to sink the boat.

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  • $\begingroup$ 3~4 times per hour? Wikipedia has the siege of Lisbon (1147) with a stone every 15 seconds alternating between 2 engines. And I have read that a benefit of trebuchets of mangonels (roman style) was their faster rate of fire. $\endgroup$ – Tyson of the Northwest Dec 6 '14 at 2:14
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    $\begingroup$ Also, I am talking about a trebuchet (used counterweight), possibly one with the split counterweights, not some form of tension based launcher. Also, most of the vessels of that period had a 60-80 ton displacement. a .5 ton or even a one ton counterweight would not over burden such a vessel. $\endgroup$ – Tyson of the Northwest Dec 6 '14 at 2:19
  • $\begingroup$ @TysonoftheNorthwest 3-4 is about the maximum speed with idea conditions. I don't know what you mean by 2 engines but the Wikipedia page has no link of reference. If such trebuchet exist, I would like to see it. $\endgroup$ – Vincent Dec 6 '14 at 2:50
  • $\begingroup$ @TysonoftheNorthwest the catapult only use torsion but the trebuchet use counter weight and torsion in the mast. Pulling the mast toward the ground generate a lot of tension. As for the weight, the french Wikipedia page state that it's between 10 to 18 tons for a standard trebuchet but again, there is no reference. $\endgroup$ – Vincent Dec 6 '14 at 2:59
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A trebuchet on a ship is entirely possible. The key benefit is that since trebuchet is a counterweight engine, it can be built to be powerful without shaking the ship apart when it is fired. The downside is that since it is a counterweight engine, it introduces large moving masses to something already unstable. Trebuchets also need to be relatively large to make sense.

The most realistic use would be as a siege weapon. The ship would sail to target, anchor itself securely, remove masts and rigging, assemble the trebuchet on deck and start firing. The ammunitions and the counterweight would double as ballast. The main structure for the trebuchet would also serve as base for the main mast. If the ship only had a single mast, it would be possible to use the arm of the trebuchet as the main mast, but it is probably better not to, as the stresses are different.

The trebuchet would fire lengthwise to avoid capsizing from sifting masses, and the deck would have a lengthwise opening to make space for the arm and counterweight to swing. Basically the arm would swing down enough that loading the trebuchet from the ammunition in the ballast would be easy. The opening would be coverable for sailing. The visible difference would be that since the counterweight needs to swing freely below the point of attachment to avoid breaking the ship, the mast attachment would look unusual.

Also the ship would be rather large since building small trebuchets is not really sensible. Probably a modified merchantman. Large, slow, carries lots of ammunition, has good stability, and is easy to acquire.

A trebuchetship could actually be useful for naval engagements. Many famous naval victories were gained by tricking the enemy into waters where their maneuvers were restricted and they were unable to use their numbers. Large number of ships congested into a small area would make a pretty good target for a trebuchet. Hitting anything would be pure luck, and the rate of fire would be slow, but a ship unlucky enough to be hit by a trebuchet would notice it. But that would be incidental, the intended use would be as a mobile siege weapon for raiding fortified coastal targets.

Also floating trebuchets would be used against the seaside defenses of cities, but those would probably be rafts or barges built on site, not trebuchetships.

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With a little Google, I found a research paper dealing with trebuchets, and it speaks of their use on ships. It only mentions ship-based usage against land-based targets, specifically cities, which makes much, much more sense than using them against other ships--you have no need to maneuvre, and you have a much larger target to aim at. Obviously they made that work somehow. I only skimmed the extract; you might be able to get more detail out of it.

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