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Published by Samuel Penn.

Also, see my profile for things that interest me.

Glendale Website - My main web site.

Yags - Main site for yet another game system, a generic GPL'd tabletop RPG.

Yagsbook - Documentation on the Yagsbook RPG documentation format, a Sourceforge project.

Mapcraft - Documentation on world mapping tools, another Sourceforge project.

Midnight Saga - An Ars Magica campaign.

Active Topics

The current topics are currently under active development (relatively speaking).

Yags is Another Game System - Game design notes for Yags, a Free roleplaying game system I use as the core system for most of my campaigns.

Yagsbook - Notes on an XML based documentation system I use for documenting Yags and related campaigns.

Full Thrust - Notes on Full Thrust

Stargrunt - Notes on Stargrunt.


Starships in Yags


The big question, is what scale to use - i.e. what represents unity for the various aspects of acceleration, distance and time. Ideally, an acceleration of 1, for one turn, will cause a ship to move 1” (assuming models are being used) per turn. The parameters are:

  • Acceleration. How quickly a ship accelerates. For Traveller, I think it's safe to assume that unity is 10m/s/s (approximately 1g).
  • Space. How far 1” on the table represents in the game. This could be anything from 1km to 1000km. It could be outside these scales, but I consider these upper and lower bounds to be reasonable.
  • Time. How long is a single turn? A standard Yags round is 5 seconds, so a turn shouldn't be shorter than this. It shouldn't be longer than 15 minutes (for no good reason other than I think this is long enough).

Example Scales


Classic Traveller actually had effective ranges in light seconds, and turns as ~15 minutes. I don't like ranges at this scale simply because it makes small ship combat boring - it's difficult to imagine dogfighting fighters or gunboats at this sort of scale. However, the values it gives are below.

Unit Value
Acceleration 1g
Space 10,000km
Time 1000s

Pretty much everything is a point target at this scale. Even Earth sized planets are barely more than 1” across, and will have little effect on combat.


As in the MMORPG. For an Eve style of combat, weapons ranges tend to be in 10s of km. Combat is relatively short, so turns should be no more than a minute or so.

Assuming 1g acceleration, and a 10 second turn, acceleration for one turn gives a velocity of 100m/s, which is 1km/turn.

Unit Value
Acceleration 1g
Space 1km
Time 10s

The biggest issue is that many large ships aren't point targets. Traveller isn't too bad (all ships are < 1km in length), but something like a Super Star Destroyer is 17km long, and becomes a terrain feature itself. You need to think about how distribution of weapons on a ship effects things (targets at one end, can be out of range of weapons at the other end).

However, combat is relatively dynamic, and close to Yags in turn length. Fighters can in theory see each other (just about), and take an active part in the battle.

This scale is very different from Traveller norm however, but probably sensible for Babylon 5 (though still too large scale for Star Wars style combat). Planets are represented by a table edge - only very small asteroids will fit on a map.

Full Thrust

My figures for typical full thrust assume 15 minute turns, and 1000km as the distance scale. This also assumes an acceleration of 1/8th of a g however (the figures are actually approximated).

If we use 5 minute turns (300s), and 1g thrust, then 1 turn of acceleration if 3km/s, or 900km/turn. This is approximately 1000km/turn, so round up for simplicity.

Unit Value
Acceleration 1g
Space 1000km
Time 300s

This gives reasonably long ranges, and has the advantage that planets are most useful (IMO) at this scale (small enough to fit on most maps/tables, large enough to be a terrain feature). Most ships are point targets, which means we don't have to worry about size/shape and distribution of weapons.

However, small ships and fighters become less interesting. Fighters cannot see each other at this scale, and 5 minute turns means combat is tactical rather than action movie.

Middle Ground

A middle ground would consist of 100s turns (approximately 2 minutes - 100s is a strange value, but means we don't have to approximate the other units). Acceleration at 10m/s/s for 100s, gives 1km/s, or 100km/turn.

Unit Value
Acceleration 1g
Space 100km
Time 100s

Planets are too big to be represented as terrain (Earth = 128” diameter), but there is a feel of vast distances so even big ships won't be seen at most combat ranges. Fighters are somewhat abstracted, but planetary bombardment (and defence) can happen at large distances.

yags/starships/start.txt · Last modified: 2015/02/04 22:40 (external edit)