Compromise and Conceit

You came in that?

Our PCs have had their first battle on board their ship, and I have been forced to think in detail about how large it is and how it is laid out. This is difficult, because many RPGs give guidelines on what to put in your ship and how much it costs, but very few talk about how it should all be laid out, how big it is and what it all looks like in the end. Some early games like Traveler provided deckplans but the ships they provided were very closely modeled on nautical ships and had a lot of flaws in their design (including that the final deckplans didn’t much match the design). So I did some thinking about how ship sizes and scales work in the Third Horizon, and came up with some guidelines, as well as some house rules for ship design. This post summarizes them.

The motivation: The Beast of Burden

The PCs’ ship is the Beast of Burden, a Class IV converted luxury yacht that they use for exploration and – as little as possible – combat. I have described the Beast of Burden elsewhere but its key modules of interest for ship design are:

• 4 Luxury suites and 16 standard cabins
• Two hangars, each capable of holding one class II or two class I ships
• A single cargo hold, which in the original rules should hold 250 tons of cargo
• A salvage unit
• An arboretum

I ruled at the start of the game that the arboretum is a module, not a feature. The Beast of Burden is also armed and has various other modules, but for the purposes of ship design I think the ones listed above are crucial. So I need to figure out how all this is laid out and what it all looks like.

Ship size: The surprising scale of Coriolis ships

To figure out ship size I thought about hangars. These are the largest components of a ship, and are available from Class III up. A Class III ship should be able to hold a single Class I in its hangar, and a Class V should be able to hold one Class III. We can make some judgments from this. First of all, how big is a class I ship? It has 3 modules, so let us assume that each module is either a hangar capable of holding some small air raft or similar sub-orbital vehicle; or that each module is a 5x2x1 m cargo hold [for more on cargo holds see below] then we could imagine that if we laid these modules end to end the longest they would reach to would be perhaps 15-20 m long and 5 m wide. Add on a 5x5m floor plan for the bridge, and then a general padding for the external shell of the ship, engines etc, we can imagine that the longest a Class I ship would be is about 30m. Perhaps its total dimensions would be a maximum of 30m x 20m x10m.

This tells us that a Class III ship hangar would have to be about 50m x 30m x20m to comfortably fit such a ship. Realistically a Class III ship couldn’t have more than 4 modules for hangars, and we could imagine laying them in a 2×2 pattern (or in a ring of 4). So a Class III ship’s hangars alone could be 100m x 60m x 20m, or a cylinder 50m long and 60m in diameter. Add in some extra space on each end for cargo, service, engines etc and we can imagine the maximum size for a Class III ship would be about 150m x 80m x 30m. A Class IV ship needs to be able to hold 2 Class I ships in a single hangar, so that hangar must be about 100m x 50m x 30m. A Class IV ship could have 8 or maybe even 12 hangars, so its maximum size (with padding for crew space etc) would be 350m x 150m x 80m. Based on this we can present the following table for ships in the Coriolis system.

The Beast of Burden herself is approximately 240m long, which makes her about the length of a Panamax cargo ship – some of the biggest ships used on earth[1]. Most of this is on the service deck, which holds two hangars, the salvage unit and the cargo. Without these modules she would be much, much smaller, but a Class VI ship with a hangar needs to have a hangar large enough to fit her, so its hangars need to be at least 300m long – in fact they need to be large enough to hold a much bigger Class IV ship than the Beast of Burden, which is why a Class VI ship can be 1.2km long.

Astute readers might notice that the weights given here are huge. I found some guidelines for calculating the weight of an ocean-going ship which suggest its weight is its volume divided by 5, and I have calculated the spaceship weights on the assumption that they would be half the weight of an equivalent-volume ocean-going ship. The reason for these enormous weights is that a terrestrial ship is long and slim, but no such restrictions apply to a spaceship. The Knock Nevis was 70m wide and maybe 80m in height, while a Class IV ship is twice as wide and higher as well. These larger volumes lead to much greater weights. In any case, in space weight is unimportant, so the main concern is volume, not weight.

For comparison purposes, I estimate the Coriolis space station is about 4.8 km wide and 7km long, making it a Class IX ship.

Dimensions of some components

It’s worth noting that ships of the same class can be remarkably different in size. A Class I ship with three weapons modules might be only 10m long, and a class IV ship that was devoted to carrying pilgrims in coffins might be only 100m long. Without hangars and cargo we can expect they are much more compact, but the ship class is decided by the total quantity of its components, not its size. Let us consider the size of some of these components.

For living space, I assume that a luxury suite is a 10mx10m floorplan, while standard suites are 5mx5m. I assigned 1m3 of space to the service station per 10m3 of volume of the ship. I decided not to measure cargo by weight, but instead by volume – 1 ton of cargo can be tiny if it is iron ore, or large if it is raw cotton. So instead I assign 10^class m3 of volume to cargo per module (so a class IV ship cargo module is 10,000 m3). The salvage station should be half the size of a hangar on a ship of that class. For class 1 and class II ships I assume a hangar (for sub-orbital small vehicles) might be about 10mx5m. Everything else I consider to be malleable in size and allocation, and I assume extra space for luxury suites or shared living space is natural. Docking stations, etc. scale up with the ship.

I assume the height of a deck for living space is 2m, or 3m if the ship is spacious, plus 1m per class of the ship. The Beast of Burden has two levels on top of its service deck, so as a class IV luxury yacht each of these levels would be assumed to be about 7m in height, with 3m of actual space experienced by the people in the ship. Obviously service decks don’t follow this plan.

Finally, I multiply the total volume by a small amount (perhaps 10%) for super structure, and then by a percentage equal to the cost inflation of the ship’s features. So if a ship’s features make it cost 30% more, then it also takes up about 30% more volume.

House rules for ship design

I made a few house rules for ship design, which I list here.

• Cargo by volume: As mentioned above, I think cargo should be measured by volume. I assume 10^class m3. On a class IV ship this means one module takes up 10,000 m3, which is a 100mx10mx10m cube. On the Beast of Burden this is two sections, each 25mx20mx30m, forward of the hangars. A Class IV ship with 12 modules devoted to cargo could have 200mx60mx10m of space, 100mx60mx20m, and so on. By way of comparison I think the largest super-tankers can hold about 500,000 m3 of oil, about 4 times as much as a Class IV bulk hauler.
• Divisible modules: If modules scale with class, I have decided ship designs can swap a single module for multiple smaller class modules. So for example a single class IV module could be composed of two Class III modules, four Class II modules, or eight Class I modules. So instead of having 64 stasis pods, a Class IV ship could opt for 32 stasis pods and an extra 8 escape pods (both class III modules). This will cost more because module price doesn’t scale with class, but it makes the ship design more versatile
• Extra class I modules: For ships of class III and above, a couple of free class I modules can be chucked in to represent the vast space in these designs. These ships get 2^(class-2) extra class 1 modules, so a class IV ship gets 4 extra Class 1 modules. For example, an extra tiny hangar for sub-orbital vehicles, one more coffin, an extra escape pod, etc. This is just flavour.
• Prison modules: The cabins module can be exchanged for a prison that holds as many people as the coffins option. Put it next to the medlab for added torture chamber options.
• Hangar expansion: The rules suggest that the number of ships should increase as 4^class (so a class V ship can hold 16 class I ships) but this is madness: I have chosen to make it 2^class. On my calculations this means that Coriolis station can hold up to 192 class I ships at any time. I think that’s okay!

With these rules it’s easier to design flexible ships that suit their purpose.

Ships beyond Class V

I have included ships up to Class IX in my table of sizes to allow for the Coriolis to be described by the rules. I have not considered how modules, hps etc. scale up with these sizes, but a basic progression from the rules would suggest a Class IX ship has 640 modules, 24hp and 11 EP, and 17 armour. I would guess that some of these values (particularly armour and hp) would scale further, and modules might plateau, so you might expect 400 modules, 40 hp and 30 armour or something similar. That’s basically indestructible. Good thing there’s only one, and it’s not mobile!

Conclusion

The Coriolis ship rules lead to staggeringly large and very cool ships, with a lot of variation in size and structure within a class, and a lot of flexibility to describe different ship designs. Coriolis station is outside the core rules, but probably the way the rules work they could be scaled up to describe Coriolis station accurately. It’s likely that your PCs will encounter ships up to 1 km long, and they’re probably flying in some rusting hulk that is bigger than most ships on earth. I think there is a problem with Class 0 ships – we need some designs for in-system fighters but the current rules don’t support that – but otherwise the rules scale well and it works nicely. By adding dimensions to some components and changing the size of cargo, it’s possible to come up with some guidelines for how to lay out deckplans and design ships that are awesome in scale and lots of fun to fly in.

I want my spaceships big and exciting. I’m looking forward to the moment my PCs encounter a 1km long spaceship, and have to negotiate …

Edit to add:

I have house-ruled the hangar module to allow the hangar to carry more ships of lower class at a rate of 2^(class step). So a class 4 ship hangar can hold 1 class 2 ship or 2 class I ships. But the official rules say this should happen at a rate of 2^(2*class step). So a class IV ship hangar holds 1 class II ship or 4 class I ships. This leads to a really rapid rate of increase of ship sizes, even if we make generous assumptions about how small a class I ship is. For example, suppose we say the biggest a class I ship can be is 15m long and 10m wide, and a hangar should allow 5m on all sides of this ship. So a class I ship needs 25m x 20m of space in a hangar. Then a class III ship hangar would need to be 25mx20m in size, and the largest a class III ship would be would be perhaps 70m x 50m, if it had four hangars. However after this hangars scale up rapidly! A class IV ship hangar would need to hold four class I ships so needs to be 100mx20m, and a class IV ship could potentially have 8 of these, which in a realistic cylinder shape would make its hangars 200m long and 50m across – so the whole ship is about 250m long. After this things scale fast. A class V ship hangar holds 16 class I ships and needs to be 100m x 80m or 200m x 50m, so a class V carrier could be 1km long and definitely more than 600m. Then a class VI ship hangar would hold 64 class I ships and need to be 400m x 100m, and so on. By this reckoning I think the largest ships in each class would be about 1km (class V), about 2km (class VI), 4 km (class VII), 10 km (class VIII) and 20km (class IX). These are huge! And that’s assuming that class I ships are half the size of my starting assumption. In this variant there is much more diversity of size within ship classes, and the PCs will likely never encounter a ship bigger than class IV, but it does raise the possibility that the Order of the Pariah are sitting on some ginormous battleship (let’s call it the Yamato) that is going to appear in the Kua system some time in the future and be bigger than the Coriolis …

fn1: The largest ship on earth was the Knock Nevis, which was 460 m long. Panamax ships are routinely 250m long.