Talk:Constructing Siege Engines (5e Variant Rule)

Seems like it's making it way too fast to build these, at just a half day per 50 HP. The materials cost should be about 10GP per HP, and then building (based on what canonical references say about creating items that require skill to make) would be one person-day per 25GP of item cost.

Supposing that a 50HP siege engine should cost 500GP in materials, it therefore would take twenty man-days to build from raw materials. To get it done in just half a day you'd have to have forty people working on it simultaneously and continuously, which does not seem remotely possible.

The DM would have to decide how many "bodies you can throw at" the build process, as there is no guidance for this in the DMG. Conservatively, I would assign up to 5 workers for building a large object, 10 for a huge, 20 for a gargantuan.

In which case, a 50HP Ballista (large object) costs 500GP and takes four days for a five-person team (of skilled persons) to build. Feels about right to me. And the build assumes at least one person with expertise/know-how in the design of the item.

Assembly on the battlefield is another thing entirely and would obviously be much quicker -- measured in minutes or hours. --Nathar (talk)

My original revision was based on a source I found that said that a catapult would have been built within a day, given a team of carpenters and availability of trees to cut down.

Of course, now I can't find that source. And scouring Google web results and Book results tells me that no-one has a freaking clue. I will investigate further.

I did find a few interesting tidbits, such as the possibility of cutting down ships masts for materials; and prefabricated trebuchet parts were so heavy they could only be transported by waterway. Marasmusine (talk) 07:32, 10 April 2017 (UTC)

I don't doubt your source; in fact, it reminds me of one I found that said a motte-and-bailey castle could be built in just two weeks. But these kinds of numbers, IMO, are sometimes referring to an extreme case. A Norman knight showed up on the fringes of Ireland, sent by the king to protect villagers from roaming marauders -- he conscripted over a hundred farmers to start digging a moat and felling trees, and used an existing saw mill there, and they all worked like mad, being motivated to hurry because they needed the structure for defensive purposes. They got it done in two weeks, in an extraordinary marshaling of resources.

Similarly with a catapult. There are different versions from simple to complex, small to large, and so if we are talking about one on the smaller, simpler side, and all the workers are skilled craftsmen (rather than just one being an expert and the others mere lackeys), then I'm sure there's some way to build a working catapult in one day, but I wouldn't think it's typical.

So I think the really good point you are making is that by adding proficient craftsmen rather than casual laborers, you should be able to cut the build time. --Nathar (talk)

I spent a good hour this morning searching the web, and Google books, and Google scholar, and not a single article or paper I read mentioned how long it might take to build these things. I even read a scholarly article about a team that rebuilt a trebuchet and they just failed to say how long it took.

The only thing I did find was the construction time for the warwolf - 3 months, requiring 5 master carpenters and 49 laborers - which is an extreme example. Marasmusine (talk) 19:27, 10 April 2017 (UTC)

That's a great example -- it's good to identify the far extremes of the spectrum. It makes me realize the size of the object needs to be considered in the scope-of-work and cost estimates. So the basis of 10GP per HP cost would be for medium size objects, and then it should probably increase at each size level, i.e. 20GP per HP for large, 30GP per HP for huge, 40GP per HP for gargantuan. That would put the massive Warwolf at 8,000 GP cost, or 320 man days (e.g. a crew of 32 working for 10 days) which is in the ballpark of being realistic. --Nathar (talk)

I should note that the stats I came up with for the warwolf are for something smaller than the real warwolf. I probably set the HP to be the "typical" gargantuan size (35 or 40 ft?) whereas the real warwolf was 60ft high. I think the 3 months build time would represent 400 hit points or more.

Hit points doesn't necessarily translate to the amount of materials used. I believe that hit points would be roughly proportional to the cross-section of the engine. Here's what build time might look like if we just look at the size of the engine.

Size	Laborers	Carpenters	Days
Medium	2	1	2
Large	4	2	4
Huge	8	3	8
Gargantuan	16*	4*	16*

*or more

Marasmusine (talk) 08:52, 11 April 2017 (UTC)

I agree about HP not necessarily translating to scope-of-work. It's the kind of thing they typically do in WotC materials to simplify things. I like your table, though. How would this affect cost? We need reasonable materials costs that start in the hundreds of GP and go up into thousands, IMO. You can compare the cost of structures in DMG p.128 -- a trading post is 5000 GP and 60 days. I would think the larger siege items, such as a siege tower or a trebuchet, for example, have to be in the ballpark of cost, complexity, time, labor, as a trading post, at least. --Nathar (talk)

Not sure yet, but we do know that if you are building one using materials in the field, you just have to pay the workers: 2 sp per day for laborers, 2 gp per day for carpenters) I just looked at an old Dragon magazine article (issue #199) on siege engines, and, rats, they didn't give any costs. Marasmusine (talk) 21:31, 11 April 2017 (UTC)

I feel that this should take into account the damage output per round, and maybe some exotic materials. For example, a wall with 1000 HP is worth 10000 GP, but a 20 HP repeating crossbow that shoots oversized javelins if only 200 GP, even though it likely much more powerful and complicated. Here’s a formula I made that I think is good for something like this: Cost in GP = (Siege Engine HP * 10) * (Tons, or less, of Exotic Materials + 1) * [1 + (Maximum Average Damage Output per Round / 100)]

By tons, or less, of exotic materials, it means that, say you want to build a mirror to blind and burn your opponents with the power of the sun, you’d need silver, glass too, but I wouldn’t consider that very exotic, if there is no exotic materials, which in this case there is, it’s priced normally, if there is one, silver, then it is priced twice as expensive, if there is silver and you count glass as an exotic material, it would be three times as expensive. This is mainly here to make sure people don’t make Rube Goldburg machine that shoots a laser. The reason I have tons listed here is because if somebody makes a siege engine made out of 10282 tons of pure gold, it’s going to be worth more than something made of only 1 ton of pure gold.

I also put damage output there to judge how strong it is, because the more damage it deals, the more complicated or resource dependent is, probably. The weird equation with the damage stuff basically means percentage, if you but all your eggs in one basket and have every action you can be focused on attacking, the average number of damage you deal on an attack like that increases the price of the weapon by a percentage equal to said average damage. If you deal an average of 50 damage per round where you only attack, the engine will be 50% more expensive.

Let’s do an example. A mounted mithral crossbow. Say it takes an action to attack, load, or aim. If we use your action to attack, which say, deals 2d12 damage, that has an average of 13 damage, let’s not overcomplicate things. It’s made of mithral, and say, has 120 HP. Here’s what the equation would look like for this example: Cost in GP = (120 * 10) * (1 + 1) * [1 + (13 / 100)

Now let’s simplify that. Cost in GP = 1200 * 2 * (1 + 0.13)

A bit more. Cost in GP = 2400 * 1.13

And finally solve it. Cost in GP = 2712

Now that is pretty expensive, but that leaves AC wide open, so it can be roughly anything. But let’s make it a rule that it can’t exceed 30, or whatever the DM deems so, but let’s make this a formula for ease of access, if the AC of the siege engine is greater than 20, subtract the AC of the siege engine by 20, then multiply the cost of the engine by the result, so if it’s AC is 24, it gets a +4 multiplier, making it 4 times as expensive. If the AC is less than 20, subtract 20 by the AC of the siege engine and add 1, then divide the cost of the engine by the result, so if it’s AC is 18, it would get a +3 divider, making it three times cheaper. Now remember that the formulas are for for homebrewing siege engines, not simply constructing it.Kanon (talk) 16:53, 2 June 2020 (MDT)