CT Only: CT power plant fuel formula

[Dr_Skull]

I've started up designing a few CT book 2 ships lately, and am a little confused by the Power Plant fuel formula.

It says 10Pn: 10 times power plant number
But, power plants come in Letters, not numbers.
And I'd think the size of the ship should have some impact on the power plant requirements.

I cobbled something using a standard ship for comparison, but how does the formula actually work?

 

[robject]

I've started up designing a few CT book 2 ships lately, and am a little confused by the Power Plant fuel formula.

It says 10Pn: 10 times power plant number
But, power plants come in Letters, not numbers.
And I'd think the size of the ship should have some impact on the power plant requirements.

I cobbled something using a standard ship for comparison, but how does the formula actually work?

Pn "number" is the rating in Gs. Ship size has no impact on fuel requirement. Consider this a compromise between requiring fuel and having the power plant be some sort of fusion reactor.

But: also see my "Book 2 Plus" rules (stickied), which extends and rationalizes Book 2 in gentle and reasonable ways.

 

[mike wightman]

You get the number from the drive table.

The book 2 formula is hopelessly broken.

A model A pp in a 100t ship requires 20t of fuel, while the same pp in a 200t ship only needs 10t of fuel.

A better formula is the one from HG, 0.01 x hull size x pp number.

 

[Matt123]

Not broken, different. As a butter knife is different to a steak knife, yet neither is broken.

If you want book 2 drives, you have to use all book 2 drives which can bring advantages. But you can't mix and match to get the best of the drive formulas from book 2 and book 5. (err.. hold this thought, trying to find a reference...)

 

[atpollard]

Not broken, different. As a butter knife is different to a steak knife, yet neither is broken.

If you want book 2 drives, you have to use all book 2 drives which can bring advantages. But you can't mix and match to get the best of the drive formulas from book 2 and book 5. (err.. hold this thought, trying to find a reference...)

On the issue of Book 2/Book 5 min-maxing, I agree.
However, this ...

A model A pp in a 100t ship requires 20t of fuel, while the same pp in a 200t ship only needs 10t of fuel.

... is really hard to view as a 'feature' rather than a 'bug'.
If I put the engine in a smaller car, its gas mileage goes down?

 

[Matt123]

If I put the engine in a smaller car, its gas mileage goes down?

Only if you assume fuel consumption is tied to the G's generated, which is not the case with CT starships (can't speak to later editions) where PP fuel consumption by MDs is inconsequential (HG p17).

On the point I made regard not mixing and matching BK2 & BK5 drives, I cannot find a reference - leading me think this 'rule' may be a Matt'ism... One I think makes good sense, but still, ummm, not a rule I can find in CT cannon or errata.

 

[atpollard]

Only if you assume fuel consumption is tied to the G's generated, which is not the case with CT starships (can't speak to later editions) where PP fuel consumption by MDs is inconsequential (HG p17).

On the point I made regard not mixing and matching BK2 & BK5 drives, I cannot find a reference - leading me think this 'rule' may be a Matt'ism... One I think makes good sense, but still, ummm, not a rule I can find in CT cannon or errata.

My assumption is only that a PP A is a PP A and the fuel consumption should not change for the same Power Plant.

No, the not mixing rule is in High Guard (1980 edition, page 22, under "Drives:") ... it actually says that Book 2 Drives use Book 2 fuel formulas.

 

[Matt123]

My assumption is only that a PP A is a PP A and the fuel consumption should not change for the same Power Plant.

I put it down to technological magic. I can't explain jump-space either

No, the not mixing rule is in High Guard (1980 edition, page 22, under "Drives:") ... it actually says that Book 2 Drives use Book 2 fuel formulas.

Yeah when I read that, it specifically allows standard drives, but does not specify that all drives must be either standard or custom. Something for Don's errata perhaps?

 

[rancke]

But: also see my "Book 2 Plus" rules (stickied), which extends and rationalizes Book 2 in gentle and reasonable ways.

Reasonable? So you pretty much eliminate power plant fuel consumption then? :devil:

Seriously, the self-contradictions of Book 2 design aside, once power plants became explicitly fusion plants, any pretense that they gobbled tons of fuel per month went right out the window. Reaction drive mass, maybe; fusion plant fuel, no way.

Also, I'm not too fond of the fact that the power plant apparently ran as if the maneuver drive was going full throttle, even in jumpspace and when not moving, and all energy weapons firing 24/7. And even if you assumed that by TL15 no one had figured out how to run the power plant at reduced rate, no one had thought of giving a ship three power plants, one for daily power consumption, one for maneuvering, and one for weapons use. That seems utterly unbelievable to me. Even with those ridiculous fuel consumption rates, a ship spending 14 days a month in jump space, 8-9 days in orbit or down on the surface, and very rarely using its weapons should be able to go 10 weeks or more on one load of power plant fuel. Or, more likely for merchants, a month with half the power plant fuel tankage.

No, Book 2 design is just too riddled with contradictions to work for me.


Hans

 

[kilemall]

Re: fuel usage, I treat the typical 4-week 'operations month' as 2 weeks under full jump, 1 week accel, and 1 week idle (my high end starports require power plant shutdown, so maybe lower even then idle).

If the travellers don't hit the power plant that heavily, they get more 'weeks' without having to refuel.


As to the OP, the Pn is derived from the plant rating not the drive letter, so as pointed out above, a power plant A is rated as 2 on a 100 ton hull and 1 on a 200 ton hull.

I don't really have a problem with the discrepancy as 100-ton scouts have the special ability of running on unrefined fuel, so it's more a loss of potential space use then anything else.

 

[boomslang]

If the travellers don't hit the power plant that heavily, they get more 'weeks' without having to refuel.

I noticed some years ago that B2 PP fuel requirements do not explicitly state the rate at which the fuel is consumed, only that 10Pn is "sufficient" for four weeks' operation.

When you take into consideration the elaborate fuel use tables from Beltstrike, it becomes clear that B2 PP fuel requirements tend to be on the generous side, as B2 Powerplants tend to consume fuel at a rate approximating that of B5 ones.

So I figure the B2 powerplant fuel requirements are regulatory, not operational. Therefore in practice IMTU, B2 powerplants sip fuel at a rate based on HG-EP-equivalency. Actual fuel use per 28 days would then equal 1dton per EP; the rest is a mandated safety margin so planetary navies are not constantly tasked with rescuing free traders who are too cheap to top their tanks up after every jump.

Some years ago, Thomas House posted a handy chart showing how these equivalent numbers would work in terms of EP-per-powerplant-letter to the ct-starships list, reproduced here below to save me having to search for where I have posted it before:

A 2
B 4
C 6
D 8
E 10
F 12
G 14
H 16
J 18
K 20
L 22
M 24
N 26
P 28
Q 30
R 32
S 34
T 36
U 38
V 40
W 50
X 60
Y 80
Z 120

Note that larger hulls with larger drives using this chart to base fuel consumption upon may actually be underfuelled at the 10Pn dtons rate; this is relatively trivial to fix by increasing their powerplant fuel tankage a few dtons -- or not if you want to limit range and thereby discourage hijacking and so on.

Also note that these implicit EP numbers could limit computer sizes and lasers mounted, especially in smaller hulls. That the model-A powerplant only puts out 2 EP accounts for why there are no triple-laser-mounting Type S starships running around out there, for example. These sorts of implicit EP calculations are also probably what limit computer and weapons fits in small craft in later editions of CT/BT, so precedent is there in the canon if you want it.

 

[kilemall]

Well, if I don't drive Aramis to drinking first, I may actually work through using the Striker rules for fuel consumption to work out exactly how much fuel the ships are using.

It has an explicit fuel to power plant tonnage ratio which can literally give you a fuel use value. Reduce that plant to minimum power, probably can justify a lower fuel use.

Not sure you can drop below a minimum one ton in use setting, which may explain the higher burn rate of the LBB2 scout (along with the unrefined part).

High Striker is wonky fun.

 

[mike wightman]

This is what the folks who designed Mega Traveller did, and broke ship design in the process.

They found they needed way more fuel for the power plant than HG fuel requirements and as a result opted to reduce jump fuel requirement - hence splitting MT ship design off into its own little drive paradigm completely at odds with every other version.

 

[kilemall]

This is what the folks who designed Mega Traveller did, and broke ship design in the process.

They found they needed way more fuel for the power plant than HG fuel requirements and as a result opted to reduce jump fuel requirement - hence splitting MT ship design off into its own little drive paradigm completely at odds with every other version.

I kind of gathered reading between the lines that MT plays more like Triplanetary with the fuel burns then anything else. Which isn't a bad thing, just not the easygoing go where I will vibe most Traveller players are accustomed to.

Hmmm well now you got me wondering.



Ok to get a power plant A on Boomslang's posted chart we need a 500 MW fusion reactor, since 1 EP = 250 MW.

At TL9 we can get 6 MW per cubic meter. We need approximately 84 cubic meters of power plant or 6 tons, 2 tons over (at higher tech levels it would be smaller).

Cost 16.8 MCr, twice the LBB2 rate.

The fuel burn rate is 1 liter per megawatt per hour. So 500 liters per hour at full power.

Traveller fuel ton is of course 14,000 liters.

So at full power that ton will last 28 hours.

20 tons of fuel, you have approximately 23 days- right in range of a reasonable two jump/transit 8 days on planet/station set of activity.

Same plant at TL 13, 9 MW per cubic meter. Requires 56 cubic meters, 4 tons so right at LBB2 value but still 11.2 MCr. Fuel use the same.




Ok, let's take on a Type C Merc Cruiser, power plant M or 24 EP by the chart, requiring 6000 MW or 6 GW. We'll use TL 13 since that seemed to result in matching size if nothing else.

9 MW per cubic meter again at TL 13, that's 667 cubic meters of power plant or 48 tons, more room needed then LBB2's M plant size of 37 tons, and more expensive at 133 MCr vs. 96.

6000 liters per hour, a Traveller ton of fuel will only last 2.33 hours. Type C has 30 tons set aside, that would only last- 70 hours, almost 3 days. The ship has that 48 ton reserve, so it could get up 182 hours or 7.58 days- long enough to jump then run out.

HG doesn't help, it comes up with 24 tons for power plant fuel tonnage.



So Striker fusion power plants out of the box do not scale well for fuel use, not surprising.

There IS the scaling rule, the bigger the plant the more efficient it is, up to 3x the base output per cubic meter at one starship ton. That could be extended to deliver 'proper' sizing and plant cost-but does nothing for the flat fuel usage rule of 1.5 liters per megawatt-hour.

Nor does any of this address fuel usage for reaction drive, if that is part of one's conception or at least in use at lower TL.

 

[aramis]

I kind of gathered reading between the lines that MT plays more like Triplanetary with the fuel burns then anything else. Which isn't a bad thing, just not the easygoing go where I will vibe most Traveller players are accustomed to.

Nope. It was TNE that counted fuel burns.

Striker fuel rates are the same as MT fuel rates...
the 0.003 is 333 hours per Td of fuel, or 1.9 weeks (13.8 days) per Td of fuel for each Td of PP, while the .005 is 1 per 200 hours, and 8.3 days.

 

[kilemall]

The easier method would be to simply say that Striker power plants are built for fuel-guzzling Army operations in small engine quarters to achieve vehicle purchase, transport and armor savings, as opposed to a much larger energy efficient 'proper Navy' power plant

So, going that direction, I am choosing to define 'normal operations' to be 20 days at full power for a two jump/transit/5 days each trip on planet/station for a full 30-day cycle. I would expect in-system transport or patrol to be similar.

The HG rules are set up, and clearly state, that 1 EP-month uses 1 ton of fuel. About as simple as it gets.

Using the 2:3 normal use ratio, that's 7,000 liters or half a ton per 10 days of full power, or put another way 29 liters per hour per EP. Translated to Striker terms, that's .116 liters per hour per MW generated.

Size apparently matters in efficient fuel use in fusion power generation.

So there you go, 29 liters per hour per EP.

Now, apply this to the LBB2 power plant fuel use formula, and you don't get a 'normal month'.

Scout ships would use 2 tons per month, so the LBB2 20 ton fuel tank gives it 10 operating months- perhaps actually a design goal one might want especially on the frontier, and belters would love their seekers. On a practical basis, could be more like getting an extra Jump-1 and 5 months of ops.

Type A free traders with 10 tons of fuel would get 5 months of operations not counting jumps- again, might be worth it if one could get decent in-system hauling rates.

And that's just counting normal ops, with fuel conservation on life support levels you might go a lot longer.

Going to the Type C with it's M plant, that's 30 tons of fuel vs. 24 ton per normal month, so the C has some reserve past one month, and the 48 ton extra could put it on station an additional two months.

The ratio holds if you gave an 800 ton hull a power plant 1 rating, say the minimum D plant, that would be 10 tons of fuel vs. 8 tons of use per normal month, you've got some margin.

Where the LBB2 fuel allocation hurts is larger ships. For instance, a 2000 ton mounting a J plant for Power-1 gets 10 tons of fuel, but 18 tons of EP to support- trending closer to two weeks' usage rather then a month.

So, a system for you to use for those drama situations where the enemy has blown the fuel tanks to heck and you are having to transfer fuel from the ship's boats and robots and air/rafts just to get a few more hours to get the ship home.

 

[kilemall]

Nope. It was TNE that counted fuel burns.

I'm sure you're right, I certainly have not done the time with any of the other systems.

Striker fuel rates are the same as MT fuel rates...
the 0.003 is 333 hours per Td of fuel, or 1.9 weeks (13.8 days) per Td of fuel for each Td of PP, while the .005 is 1 per 200 hours, and 8.3 days.

Check over my newest post, I think my numbers work out using strictly HG referring to itself, the 2:3 assumption of normal and converting back to Striker liter per megawatt per hour.

 

[Grav_Moped]

I noticed some years ago that B2 PP fuel requirements do not explicitly state the rate at which the fuel is consumed, only that 10Pn is "sufficient" for four weeks' operation.

When you take into consideration the elaborate fuel use tables from Beltstrike, it becomes clear that B2 PP fuel requirements tend to be on the generous side, as B2 Powerplants tend to consume fuel at a rate approximating that of B5 ones.

So I figure the B2 powerplant fuel requirements are regulatory, not operational. Therefore in practice IMTU, B2 powerplants sip fuel at a rate based on HG-EP-equivalency. Actual fuel use per 28 days would then equal 1dton per EP; the rest is a mandated safety margin so planetary navies are not constantly tasked with rescuing free traders who are too cheap to top their tanks up after every jump.

Repeating here something I just posted elsewhere -- but here, it's on topic:

There is a very good reason why a mandated 4-week fuel supply (however that's calculated) is appropriate: Misjumps.

Misjump duration is 1D weeks. If only 1 week of powerplant fuel is carried, then five times out of six a misjump will outlast your fuel supply, shutting down the powerplant and consequently your Jump field. And then Bad Things Happen. With one month of fuel the odds of having enough fuel to get though a misjump are 2:1.

 

[boomslang]

Misjump duration is 1D weeks. If only 1 week of powerplant fuel is carried, then five times out of six a misjump will outlast your fuel supply, shutting down the powerplant and consequently your Jump field.

This is a good point. It also raises the perfectly-reasonable question of why only 4 weeks' duration is stipulated instead of the more-useful and likely-to-be-demanded-by-the-financing-banks 6 (15Pn dtons, anyone?); it suggests that either a powerplant operating at the level of the Jump is not in fact required to sustain that Jump -- which would go against what we have since the early days either inferred (HG2) or else been more-or-less-canonically told (SoM) about how functioning powerplants are needed to burn off the charge on the Jump capacitors in a controlled manner over the duration of the Jump (hopelessly-broken OTU Xboats notwithstanding, of course) -- or else Misjump was never playtested fully back in the early days.

:CoW:

 

[aramis]

This is a good point. It also raises the perfectly-reasonable question of why only 4 weeks' duration is stipulated instead of the more-useful and likely-to-be-demanded-by-the-financing-banks 6 (15Pn dtons, anyone?); it suggests that either a powerplant operating at the level of the Jump is not in fact required to sustain that Jump -- which would go against what we have since the early days either inferred (HG2) or else been more-or-less-canonically told (SoM) about how functioning powerplants are needed to burn off the charge on the Jump capacitors in a controlled manner over the duration of the Jump (hopelessly-broken OTU Xboats notwithstanding, of course) -- or else Misjump was never playtested fully back in the early days.

:CoW:

Let's timeline...

Book/Year	PP Required to Jump	PP used for JD during jump?
B2-77	N	N
B5-79	Y	U
B5-80	Y	U
B2-81	Y	N
MT	N	N
TNE	N	N
T4	N	N
T20	Y	U

[tc=4]Y=Yes
N=semi-explicitly or explicitly not required
U=Unclear, not mentioned[/tc]

[tr]
Note that in MT, Jump Drive units have no power requirement at all
TNE is the same. T4 uses the same design sequence as TNE.

I notice a tendency for people to see a lot of ghosts that aren't in the text when it comes to Jump Drives. It's explicit that the jump drive is only holding off the weirdness of J-Space once the initial jump is committed; in SSOM, that is further refined to be a passive factor, not active.

HG 1 & 2 specify a huge ENTRY cost in power, but say nothing about power being fed to it in jump itself.