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Old 03-27-2023, 11:21 AM   #1
dataweaver
 
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Default More granular Spaceships

I originally posted this in the “Battletech to GURPS” thread; but it's more generally useful than the original topic, so I'm reposting it here with some additional thoughts:

Quote:
Originally Posted by David Johnston2 View Post
I find Spaceships insufficiently granular for something like this.
I had the same reaction; so I developed some house rules for adding granularity to Spaceships. I do this by applying fractional SMs, in increments of 0.2: if SM 4 is 10 tons, then SM 4.2 is 12 tons; SM 4.4 is 15 tons; SM 4.6 is 20 tons; and SM 4.8 is 25 tons. Likewise, if SM 5 is 30 tons, then SM 5.2 is 40 tons, SM 5.4 is 50 tons, SM 5.6 is 60 tons, and SM 5.8 is 80 tons.

More generally, every table in Spaceships uses one of three standard progressions, depending on how many SMs you need to go up in order to get to ten times the quantity. The Volume progression is a two-step of either 3/10 or 1.5/5; the Area progression is always 2/5/10; and the Linear progression is 1.5/2/3/5/7/10. I have more granular replacements for this that let you interpolate systems that fall between these values based on whether they're ±0.2 or ±0.4. The tonnages given above are an example of applying this principle to a Volume progression; but similar interpolations exist for Area and Linear progressions as well. Also: while I'm technically using decimal SMs, I round to the nearest SM in gameplay; so instead of talking about adding or subtracting 0.2 or 0.4 to the SM, I introduce size categories to use within each SM. (Kudos to mlangsdorf for this revision.) The centerline, “medium”, represents the programs found in the book; start by finding the one that matches that, then shift up or down up to two ranks for more precision.

For those who want to use them, my interpolation charts follow:

Volume Progression
This is the default progression.

Code:
  Tiny: 0.6, 2,    6, 20,  60, 200
 Small: 0.8, 2.5,  8, 25,  80, 250
Medium: 1,   3,   10, 30, 100, 300
 Large: 1.2, 4,   12, 40, 120, 400
  Huge: 1.5, 5,   15, 50, 150, 500
Sometimes the progression centers around 2/6 or 5/15 instead of 1/3. To handle these, just shift the rows:

Code:
  Tiny: 1.2,  4, 12,  40, 120,  400
 Small: 1.5,  5, 15,  50, 150,  500
Medium: 2,    6, 20,  60, 200,  600
 Large: 2.5,  8, 25,  80, 250,  800
  Huge: 3,   10, 30, 100, 300, 1000
Code:
  Tiny: 0.3, 1,   3, 10, 30, 100
 Small: 0.4, 1.2, 4, 12, 40, 120
Medium: 0.5, 1.5, 5, 15, 50, 150
 Large: 0.6, 2,   6, 20, 60, 200
  Huge: 0.8, 2.5, 8, 25, 80, 250
Area Progression
Used by Open Space, Soft Landing System, and Stasis Web

Code:
  Tiny: 0.7, 1.6, 3.5,  7, 16, 35
 Small: 0.8, 1.8, 4,    8, 18, 40
Medium: 1,   2,   5,   10, 20, 50
 Large: 1.2, 2.5, 5.5, 12, 25, 55
  Huge: 1.4, 3,   6,   14, 30, 60
Linear Progression
Used by Armor, Force Screens, and Weapons.

Code:
  Tiny: 0.8, 1.3, 1.8, 2.6, 4,   5.8
 Small: 0.9, 1.4, 1.9, 2.8, 4.5, 6
Medium: 1,   1.5, 2,   3,   5,   7
 Large: 1.1, 1.6, 2.2, 3.2, 5.2, 7.5
  Huge: 1.2, 1.7, 2.4, 3.6, 5.5, 7.8
Weapon systems introduce two complications which the above doesn't address: gun calibur/launchers, and D-damage. The former doubles every +4 SM; so it should be possible to build an interpolation chart. I simply haven't bothered to, as I don't know of any rules where this would matter.

The latter is more important: when you're talking about dice of damage, interpolation gets tricky; especially when you want to keep the existing damage dice in place.

From what I can tell, it looks like the average damage is supposed to follow the Slow Progression given above, starting around 10 D-damage. If we allow for “(xd±y)×n” for the dice formulas, we shouldn't have any problems matching any of the data points:

D-damage ratings
Code:
  Tiny: 3d–2, 4d–1, (3d–2)×2, (4d–1)×2, (3d–2)×5, (4d–1)×5
 Small: 3d–1, 4d+0, (3d–1)×2, (4d+0)×2, (3d–1)×5, (4d+0)×5
Medium: 3d+0, 4d+1, (3d+0)×2, (4d+1)×2, (3d+0)×5, (4d+1)×5
 Large: 3d+1, 5d–1, (3d+1)×2, (5d–1)×2, (3d+1)×5, (5d–1)×5
  Huge: 3d+2, 5d+0, (3d+2)×2, (5d+0)×2, (3d+2)×5, (5d+0)×5
Unfortunately, I don't see any way to do this using only xd+y and xd×y; that combination simply doesn't allow enough resolution. I also can't get it to align with the values given in Spaceships as written. But if you're willing to flat-out replace Spaceships' D-damage values, the above should do the trick.

Fine-tuning
Finally, you have the option to vary the spaceship's length by up to ±5%. Apply that directly to all Linear progression figures; apply double that to all Area progressions; and apply triple that to all Volume progressions.

———

Thoughts?
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Last edited by dataweaver; 03-27-2023 at 07:12 PM.
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Old 03-27-2023, 12:31 PM   #2
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Default Re: More granular Spaceships

I have a blog article on scaling spaceships to arbitrary sizes: I settled on using one-third sized SM's, because that made the weight follow the length/range table. Supporting it are armor tables for small and large spaceships.

I mostly ripped out the weapon system, but the pieces of it I ended up using are here.


Just a topic I've put a lot of effort into in the past.
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Old 03-27-2023, 12:38 PM   #3
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Default Re: More granular Spaceships

I had a similar concept to you, but organized it slightly differently.

Instead of decimal sizes, I had size categories: Tiny (T), Small (S), Medium (M), Large (L), and Huge (H). Tiny would correspond to 0.6 of the previous size in your system and Small to 0.8, while Large and Huge would be 0.2 and 0.4. So what you would call an SM 9.8 spaceship, I'll call an SM 10S. Not a huge deal.

I also broke the charts down slightly different. There are three progressions in Spaceships - Volume (what you call fast), Area (what you call medium), and Linear (what you call slow). I interpolated the numbers slightly differently than you did, but not hugely so.

For weapons, I noted that every weapon mount provides 30 points worth of weapon mounts. A spinal weapon requires 90 points of weapon mounts. A major weapon requires 30, a medium weapon requires 10, a secondary weapon requires 3, and a tertiary weapon requires 1. You can mix and match weapons within a mount, and choose intermediate sizes (usually based on the volume progression). So an SM 10M weapon mount could have 1 SM 10M medium weapon (1 GJ beam), 4 SM 10M secondary weapons (300 MJ beams), and 8 SM 10M tertiary weapons (100 MJ beams). Or if you wanted to get fancy, you could replace the SM 10M tertiary weapons with 5 SM 11T tertiary weapons (250 MJ beams) because each SM 11T tertiary beam takes up 1.6 weapon mounts.

And I also went through and converted all the damage values to average rolled damage, interpolated the intermediate points, and converted those back to XdxY format for every weapon. I've got a huge spreadsheet somewhere with all that work. And obviously I wrote a spreadsheet to look up all the intermediate values so I could just design spacecraft of whatever size I wanted.

But obviously, I think is a great idea. It adds a lot of flexibility for Spaceships to be able to create 6,000 ton and 8,000 ton light cruisers and have somewhat different statistics than the 12,500 and 15,000 ton heavy cruisers.
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Old 03-27-2023, 12:40 PM   #4
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Default Re: More granular Spaceships

The easy solution to scaling spaceships is (thanks Dataweaver for the categories):

Pick a scale factor S.

Multiply vehicle length/height/whatever by S.
Multiply hit points by S.
For any component that uses the Slow progression, multiply it by S.
For any component that uses the Medium progression, multiply it by S^2.
For any component that uses the Fast progression, multiply it by S^3.

Beam weapons can either use the Slow progression (in which case you multiply damage) or the Fast progression (in which case you multiply the number of weapons that can fit in a mount). I'm not sure what's up with the formulas for kinetics.
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Old 03-27-2023, 12:46 PM   #5
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Default Re: More granular Spaceships

Quote:
Originally Posted by Anthony View Post
I'm not sure what's up with the formulas for kinetics.

Extrapolating from UT, its 1.5Dd per cm of diameter. or 15d per cm of diameter, if you're personal scale.
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Old 03-27-2023, 01:29 PM   #6
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Default Re: More granular Spaceships

Quote:
Originally Posted by Anthony View Post
The easy solution to scaling spaceships is (thanks Dataweaver for the categories):

Pick a scale factor S.

Multiply vehicle length/height/whatever by S.
Multiply hit points by S.
For any component that uses the Slow progression, multiply it by S.
For any component that uses the Medium progression, multiply it by S^2.
For any component that uses the Fast progression, multiply it by S^3.

Beam weapons can either use the Slow progression (in which case you multiply damage) or the Fast progression (in which case you multiply the number of weapons that can fit in a mount). I'm not sure what's up with the formulas for kinetics.
S should be between 1 and 1.47; beyond that, you shift SM.

Alternately, S can be between –20% to +20%, with the multiples for Fast and Medium (or Volume and Area) being (1+S)^3 and (1+S)^2, respectively. I'll crunch the numbers a bit to see if it's close enough that “triple” and “double” will work.

EDIT: It's not close enough: +20% cubed is just shy of +75% (+72.8%, to be exact), and –20% cubed is a little under –50% (–49.8%). +60% and –60% miss their respective marks by double digits. If I recall correctly, I once decided that ±10% was about as large of a percentage modifier where I'd be comfortable saying that S³≈3S and S²≈2S is close enough: +10% cubed is +33%, and –10% cubed is –27%; in both cases, tripling the modifier misses the mark by 3%.

Fortunately, the added resolution provided in my original post has the smallest adjacent steps being approximately 10% apart; which means that if you want to fine-tune it further, you can allow an S of up to ±5% for the Slow Progressions, double that for the Medium Progressions, and triple that for the Fast Progressions. That gives you +15% instead of +15.76% and –15% instead of –14.26% for fine-tuning the Fast Progressions; less than a 1% error.

I can live with that.
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Old 03-27-2023, 02:03 PM   #7
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Default Re: More granular Spaceships

Quote:
Originally Posted by dataweaver View Post
S should be between 1 and 1.47; beyond that, you shift SM.
Unless you shift over a breakpoint (there's some components that stop being required at SM+10, for example), it will work fine even beyond that, you'll just have to adjust SM.
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Old 03-27-2023, 02:36 PM   #8
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Default Re: More granular Spaceships

Technically true; although you'd also need to work out how much to adjust the SM by; and that would require taking the logarithm of S.

Part of the goal there is to increase the resolution of Spaceships, which your suggestion does; but the other part of the goal is to do so without having to completely reinvent the wheel or drastically complicate the math involved. Putting bounds on S and having it work within the existing SM system does that, too; though I expect that that's still a case of overkill: mathematically sound, mind you; but the sorts of people who would be interested in that approach would likely be more inclined to want the GURPS Vehicle Design System vaporware instead of a higher-resolution patch for GURPS Spaceships.

For those who just want to patch a bit more granularity into GURPS Spaceships, interpolating another two to four levels within the existing SMs is probably good enough, especially since it allows Someone Else to do more of the math, leaving the Spaceship designer only having to pick one of the additional options provided instead of picking an arbitrary factor S and then having to figure out when to multiply by S, S², or S³.
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Old 03-27-2023, 03:03 PM   #9
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Default Re: More granular Spaceships

Quote:
Originally Posted by mlangsdorf View Post
I had a similar concept to you, but organized it slightly differently.

Instead of decimal sizes, I had size categories: Tiny (T), Small (S), Medium (M), Large (L), and Huge (H). Tiny would correspond to 0.6 of the previous size in your system and Small to 0.8, while Large and Huge would be 0.2 and 0.4. So what you would call an SM 9.8 spaceship, I'll call an SM 10S. Not a huge deal.

I also broke the charts down slightly different. There are three progressions in Spaceships - Volume (what you call fast), Area (what you call medium), and Linear (what you call slow). I interpolated the numbers slightly differently than you did, but not hugely so.

For weapons, I noted that every weapon mount provides 30 points worth of weapon mounts. A spinal weapon requires 90 points of weapon mounts. A major weapon requires 30, a medium weapon requires 10, a secondary weapon requires 3, and a tertiary weapon requires 1. You can mix and match weapons within a mount, and choose intermediate sizes (usually based on the volume progression). So an SM 10M weapon mount could have 1 SM 10M medium weapon (1 GJ beam), 4 SM 10M secondary weapons (300 MJ beams), and 8 SM 10M tertiary weapons (100 MJ beams). Or if you wanted to get fancy, you could replace the SM 10M tertiary weapons with 5 SM 11T tertiary weapons (250 MJ beams) because each SM 11T tertiary beam takes up 1.6 weapon mounts.

And I also went through and converted all the damage values to average rolled damage, interpolated the intermediate points, and converted those back to XdxY format for every weapon. I've got a huge spreadsheet somewhere with all that work. And obviously I wrote a spreadsheet to look up all the intermediate values so I could just design spacecraft of whatever size I wanted.

But obviously, I think is a great idea. It adds a lot of flexibility for Spaceships to be able to create 6,000 ton and 8,000 ton light cruisers and have somewhat different statistics than the 12,500 and 15,000 ton heavy cruisers.
I like your terminology here: Tiny, Small, Medium, Large, and Huge instead of SM –0.4, SM –0.2, SM +0.0, SM +0.2, and SM +0.4, respectively. Likewise, Volume/Area/Linear instead of Fast/Medium/Slow. I will edit my initial post accordingly.
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Old 03-27-2023, 03:16 PM   #10
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Default Re: More granular Spaceships

Quote:
Originally Posted by dataweaver View Post
Technically true; although you'd also need to work out how much to adjust the SM by; and that would require taking the logarithm of S.
Multiply length by S. Use that length to compute SM.
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