APPENDIX XXVIII: Fuel usage and storage in Leviathan and Interceptor

By Fireangel

One aspect of both space-combat RL games (Leviathan and Interceptor) that is both crystal clear and infuriatingly vague is the rules regarding fuel usage in space-going vessels.

First, let’s get some basics out of the way through review: ships in RL come in two basic types; built with Leviathan rules and built with Interceptor rules:

Interceptor-rules vessels (which we will refer to as “fighters”, for convenience, whether they are light fighters or 30k PF “patrol vessel” Escorts) can accelerate from a relative velovity of 0 to a velocity of 750 hexes per turn and descelerate back to zero… once. To borrow a term from Battletech: Aerotech, this is the equivalent of 1,500 Thrust Points.

Leviathan-rules vessels (which we will refer to as “ships” or “leviathans”, regardless of class or tonnage), can make that acceleration/deceleration twice; the equivalent of 3,000 thrust points.[1]

HOWEVER, Leviathan hexes are five times as large as Interceptor hexes and turn length is likewise multiplied by five, meaning that for practical purposes, fighters have only 300 Leviathan-scale thrust points. Since we are seeking a unified fuel rule, we can confidently state:

Leviathans: 3,000 Leviathan-scale thrust points
Fighters: 300 Leviathan-scale thrust points

This is true regardless of ship size: a 10,000 ton Capital Corvette has the same 3,000 Thrust Points as a 20,000,000 Overlord Supercarrier. By the same token, a 10,000 ton Patrol Corvette (built with Interceptor rules) would have only 300 Thrust Points.


Fighter-grade engines are designed for high performance over short periods of time; much like the high-performance engine of an F1 racer, while Leviathan-grade engines are designed for better fuel efficiency over a long period of time, like the engine in a long-haul semi truck.

Obviously, the actual amount of fuel that comprises one “thrust point” will vary depending on the tonnage of the ship (the Overlord will consume 2,000 times the amount of fuel as the 10k Capital Corvette to attain the same velocity over the same period of time. This has some very important implications; since all ships use the same type of fuel (hydrogen), larger ships can easily refuel smaller ships without much sacrifice, but since there is no means to easily calculate the relationship between one thrust point in a 69-ton fighter and a 2,674,863-ton cruiser, one is left with crude stopgap math to make do. Additionally, without a common value, there is no way to assign cargo tonnage to fuel in any meaningful manner, indirectly prohibiting the design of fuel tankers and colliers (warship-grade tankers).

Using any measure of weight or volume is pointless, since neither is used in the construction rules. This leaves us with abstract math numbers.

So what do we need to do?

  1. Establish a common unit for fuel storage (Fuel Unit [FU])
  2. Create a formula for determining how many FUs are spent for every Thrust Point used in any given ship AND how many FUs are carried by any given ship.
  3. Determine a weight value for FUs

Step one:

Formula: Ship’s mass / thrust points = fuel units per thrust point

Ship Tons:    FU per TP:
Fighter Tons:
Class          Tonnage      FU per TP
Shiva...... (4,212,757)....1,404.2523
Syracuse... (1,627,276)......512.4253
Bantha....... (966,620)......322.2066
Fulgur....... (765,033)......255.011
Serpens...... (540,775)......180.775
Xerxes....... (872,008)......290.6693
Repulse.... (2,393,570)......797.8566
Carthage... (1,253,365)......417.7883
Valiant...... (341,485)......113.8283
Exeter....... (606,027)......202.009
Ajax......... (546,676)......182.2253
County....... (910,650)......303.55
Pharetra....... (2,193)........7.31
Solstice....... (2,877)........9.59
Bumble Bee........ (69)........0.23

Once we have the FU per TP, we could leave it at that for general use: we have a perfectly workable system wherein any ship can provide fuel from its internal tankage to any other ship regardless of category or tonnage, however, we still cannot determine fuel weight alone or allocate additional tonnage to fuel.

We need to first establish that the baseline 3,000 (for Levs) or 300 (for fighters) thrust points’ tonnage is included in the tonnage of the engines, so no additional tankage needs to be allocated. However, we do need to assign weight to each FU in order to make any form of refueling rule system work.

How to do it?

We could assign an arbitrary value, but given that we are trying to achieve realistic believability and consistency, we need to find something more acceptable.

Let’s look at the fuel system of another FASA-produced game: Battletech: Aerotech. Despite differences in scale (both time and hex size), the raw acceleration factors are very similar in m/s2, enough that we can look at that system’s numbers with confidence. Since the second revision (AT2R), the standard has been:

1 ton of hydrogen fuel = 75 thrust points, regardless of fighter tonnage.

This equals:

1 TP = 13.33 kg of fuel

This seems to me to be a reasonable value. For the sake of avoiding dangling infinitives, let’s say that:

1 FU = 13.375 kg

Meaning that multiplying the FU per TP value by 13.375, we find out how much weight in fuel each ship burns per TP. Multiplying this value by 300 or 3,000 will yield the tonnage of a full load of fuel:

Lev: 13.375 x 3,000 = 4,012.5 x (FU per TP) = weight of Lev’s full tanks, in kg
Int: 13.375 x 300 = 401.25 x (FU per TP) = weight of Fighter’s full tanks, in kg

How to implement the system?

Keep in mind that cargo tonnage in the RL universe takes up 10% of total tonnage, so a ship carrying 100 tons of fuel must devote 10 tons to the actual containing equipment.

Tankers and colliers only need to list how much fuel they carry in kg or metric tons; since each ship can now list its tankage in kg, distribution should be a cinch!

(Full list pending)

Notes & References

  1. Legionnaire (RPG) pp. 116

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