”... mechanical artillery, however well developed, never quite acquired the power to bring down entire walls in the manner subsequently made possible by gunpowder and cannon ...”
That is a sentiment I intend to embrace with all my heart and mind. My world has long operated on the principle that the existence of magic has belayed or caused disinterest in the development of gunpowder as a terror weapon – in fact, the employment of a single cantrip (dampen, change, ravel) could be used with alacrity by an ordinary mage’s apprentice spy to cause a cannon to blow itself up. This logic allows me to keep beautiful castles for my Renaissance Era campaign without seriously disturbing the milieu’s credibility ... and here Rod nicely adds an additional argument.
So apart from shooting at people on walls and dropping dung, plague victims and human heads over a castle’s wall, the chief problem becomes what can be done by siege weapons against wooden targets – like other siege weapons and ships.
Well, to begin with, yesterday I pointed out that the density of wood was about half that of a human being. We can add to that the inflexibility of wooden structures compared to human beings, and we thus establish reasonably that the amount of damage which a siege weapon might do against a wooden structure would be equal to 2d6, or 1d12, per newton. (I hope you’re following here, because I’m not going over it all again – note the last four posts).
That’s twice as much as against a human target, which makes it easy and convenient for comparison and for evaluating damage. One of the annoyances in the DMG is that, on p. 110, there is no effort whatsoever to equivocate the ‘defensive point values’ listed to hit points. Of course, it probably never occurred to anyone that it would need to be ... except that I’ve found that constructions often don’t happen to exactly duplicate things that appear in the DMG, and that calculating new fortifications is a huge headache. Wouldn’t it be convenient if there was one single list that incorporated the amount of damage done by a charging knight on horseback to a human being and the amount of damage done by same said knight against a palisade fence? Believe me, in many years of playing, these things have come up.
How many defensive point value points of damage are done by a herd of animal controlled charging rhinos? Oh wait, the inventors of the game never thought to include that on the list of ‘Siege Attack Values’ on p. 109.
All right. Now people can argue as long as they like about the accuracy of this number, but I have listed on my equipment list that a ‘large ballista’ weighs 4,793 lbs. And I have argued previously on this blog that the body mass of an adult male human being (175 lbs.) would be worth 1d8 hit points (in addition to those hit points gained from skill & luck).
From these two numbers we can postulate that the number of hit points possessed by a large ballista is equal to 4,793/175 x 4.5 (average of a d8), which equals 123 hp. Taking the previously establish damage measurement from recent blog posts, I can suggest that the amount of damage done against the ballista by a 1-second shot (within the range of the missile travelling less than one second) would be equal to 20 newtons, or 20d12 (remember, twice the damage as against a living creature) ... the average of which would be 130. Now, isn’t that just bloody sweet?
I didn’t plan it out that way. I’ve been pretty much working out this system as I’ve gone along these last few days, and this is the first time I’ve calculated these figures. Just lucky, I guess.
There will be those out there who will argue that half damage or three quarter damage against the ballista would be enough to render it useless. But I would remind those voices that half damage or three quarter damage against your character does not reduce their chance to hit or do damage in any way. The 123 hp of the ballista is the amount of damage necessary to stop it from being a ballista.
Of course, it could be healed. And by my stunning rules, the ballista, if it suffered up to one quarter of it’s hp per round, it couldn’t fire (it would have to be re-adjusted and even partly reloaded).
Off hand, I’d estimate that any force applied against the ballista that would be less than 1 newton could be disregarded as non-effective, according to the arguments I made on my last post. That would exempt a swing with a dagger, but not necessarily an arrow ... which seems problematic to me. However, the arrow would have to be fired within 23.5 m of the ballista, a circumstance which wouldn’t likely come up that often. But some rule would have to be made regarding the original mass of the instrument being used to do damage.
This brings us to the question of actually hitting the target. I think I would use the DMG here, and say that the stationary target would allow a +3 to hit, and then additional plusses for subsequent shots. Unlike the DMG, however, I think that each individual subsequent shot should add an additional, cumulative bonus – not +4 as suggested, but +3. Therefore, the first shot would be against AC -10 at +3, the second at +6, the third at +9 and so on ... provided the target is not moved between shots. Eventually, you will hit a motionless target. That is because an artillerist knows that machinery ballistics, unlike the process of re-aiming with your arm every time, is a methodical series of adjustments. A skilled artillerist would know his instrument, and would know how to adjust it following each recoil and eventually hit his mark. It’s not chance. That is why artillery units quickly stop firing their weapons once they’ve come under fire, and move them forward, back, or elsewhere.
Okay. The next logical step from here would be to talk about actual buildings – specifically, ships, which is what I was working on offline that got me started on this subject. But I want to tell you, I am dead tired on this subject and I want to stop now. I will pick it up in the future, just as I intend to pick up my Civilization posts where those stopped – metal casting, which I haven’t written yet. The problem with a series of articles is that they tend to dry a writer out. For the present, then, I’ll put this down, do a little side work on ships and come back to it when I have something more to say.
In the meantime, you should be able to do the math yourself. Calculate the weight of the building and that equals its number of hit points. If you want to know a stone structure’s hit points, remember the density of stone (you can find densities for a lot of things on the SI Metric link on this blog), compare it to human flesh (900 kg/cub m, to put it in the idiom of the SI Metric site) and calculate the weight for the volume of stone represented by the fortification.