LBB2 Fuel requirements

[atpollard]

I must confess that I never used LBB2 for starship design, I LIKE the LBB5 design system. I recently tried to check the scout in the LBB2 design system and found the fuel requirements very odd.

At a minimum, ship fuel tankage must equal 0.1MJn+10Pn, where M is the tonnage of the ship, Jn is the ship's jump number, and Pn is the ship's power plant rating. Power plant fuel under the formula (10Pn) allows routine operations and maneuver for four weeks. Jump fuel under the formula (0.1MJn) allows one jump of the stated level.

So a non-starship would require 10 x Pn tons of fuel to operate the PP and MD for 4 weeks.

The DRIVE POTENTIAL TABLE on page 22 of LBB2 says "Comparing hull tonnage to drive letter indicates performance of that drive in that sized hull. Use next larger size hull for intermediate tonnages. Performance is Gs acceleration for maneuver drives, jump number for jump drives, and power plant number for power plant."

From the same table, a 100 ton hull with a MD and PP A would have 2G and Pn2 - requiring 20 tons of fuel for 4 weeks. A 5000 ton hull with a MD and PP Z would have 2G and Pn2 - requiring 20 tons of fuel for 4 weeks.

Does a 4 ton PP in a 100 ton hull really require the exact same amount of fuel as a 73 ton PP in a 5000 ton hull - 20 tons of fuel in both cases?

Have I missed something?

 

[robject]

Does a 4 ton PP in a 100 ton hull really require the exact same amount of fuel as a 73 ton PP in a 5000 ton hull - 20 tons of fuel in both cases?

Yes, that is correct. That's only one of several things I don't like about Book 2. And yet, I prefer it over High Guard for smaller ships.

'Course, nowadays I drop-in T5 ACS versions as replacements.

 

[jawillroy]

Oh, brother...

*starts stretching wrists in preparation for desperate handwaving, then gives up*

This would appear to be the case. How does High Guard do it? I forget.

 

[robject]

Oh, brother...

*starts stretching wrists in preparation for desperate handwaving, then gives up*

This would appear to be the case. How does High Guard do it? I forget.

High Guard fuel usage depends on power plant volume, essentially.

Credit where it's due: ACS' fuel usage is, roughly, HG fuel usage at around TL12.

 

[tbeard1999]

Have I missed something?

No. The maneuver fuel equation is absurd. A better solution is to drop the HG maneuver fuel equation in.

I use it because I use a nifty ship design utility (the CT Utility) that requires it. If I didn't use that program, I'd use the HG equation.

 

[Supplement Four]

Credit where it's due: ACS' fuel usage is, roughly, HG fuel usage at around TL12.

What is "ACS" again?

 

[aramis]

What is "ACS" again?

T5 Adventure Class Starships

 

[robject]

What is "ACS" again?

Sorry. Adventure-Class Ship design. Draft small ship rules.

 

[Bob Weaver]

I must confess that I never used LBB2 for starship design, I LIKE the LBB5 design system. I recently tried to check the scout in the LBB2 design system and found the fuel requirements very odd.



So a non-starship would require 10 x Pn tons of fuel to operate the PP and MD for 4 weeks.

The DRIVE POTENTIAL TABLE on page 22 of LBB2 says "Comparing hull tonnage to drive letter indicates performance of that drive in that sized hull. Use next larger size hull for intermediate tonnages. Performance is Gs acceleration for maneuver drives, jump number for jump drives, and power plant number for power plant."

From the same table, a 100 ton hull with a MD and PP A would have 2G and Pn2 - requiring 20 tons of fuel for 4 weeks. A 5000 ton hull with a MD and PP Z would have 2G and Pn2 - requiring 20 tons of fuel for 4 weeks.

Does a 4 ton PP in a 100 ton hull really require the exact same amount of fuel as a 73 ton PP in a 5000 ton hull - 20 tons of fuel in both cases?

Have I missed something?

I always converted the power plant letter to numbers, A=1, D=4, etc. and used that number with the PP fuel calculation. It scales up well: type Z plant is 18.25 times the size of a type A; fuel for type A is 10 tons & 240 tons for type Z. This goes against 'scale efficiency' a bit, but oh well.


Cheers,

Bob W.

 

[boomslang]

I always converted the power plant letter to numbers, A=1, D=4, etc. and used that number with the PP fuel calculation. It scales up well: type Z plant is 18.25 times the size of a type A; fuel for type A is 10 tons & 240 tons for type Z. This goes against 'scale efficiency' a bit, but oh well.

Back in the day, on the ct-starships mailing list, Thomas House came up with a formula that kind of splits the difference between B2 and HG2 and more or less preserves the rated EP (but misstates the HG2 fuel requirement):

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

This chart works for the entry level for each PP number
at a given book 2 hull.  For example a 2000 ton ship
with a type 2 power plant would using book 5 produce
40 EP.  A 2000 standard hual with a type V power
(entry level for plant pp2) would produce 40 EP.  

With this chart you could then use the same formula
that book 5 uses 2dt fuel x EP produced.  Plus by
doing so you could off set the advantage of adding a
few more EP by simply jumping to the next pp letter
(assuming it does change PP#) because fuel
requirements also increase.

IMTU, we go with 1dt x "EP" and just rationalize the required excess (on small ships; large ships actually have to carry more powerplant fuel under this scheme than B2's formula says) as a safety/regulatory requirement for commercial service... the SPA hates having to send out a tug to tow some drifting, out-of-fuel, hazard-to-navigation Free Trader in three times a week... plus, 1dt of fuel will run a low berth for a millennium or three, I'd expect...

 

[robject]

That's probably the same sort of reasoning that ACS used to come to its fuel usage: 1 ton per power plant letter per week of operation; typical requirements are therefore 2 tons for about 2 weeks of operation, and (I presume) military ships will have 4 tons for a month's operation.

But, the drive potential table for ACS becomes generous much sooner than Book 2 (it starts to show for hulls > 600 tons).