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Old 06-07-2018, 05:34 PM   #1
cptbutton
 
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Default Slower fuel-efficient jump drive implications?

What the implications of a slower but more fuel-efficient jump drive?

I am considering trying to rework the Islands clusters as being like CJ Cherryh's Union Alliance setting in tech. This would mean that jump drive takes 1 month external time for a 1 parsec jump, but uses much less fuel, such that a ship can jump 4-5 times without refueling while still having a lot of cargo capability. Internal time is 1 week, but because of sensory distortion people have to spend it sedated to avoid mental damage.

If the Islands developed this kind of drive and used it extensively, what would happen when the Imperium contacted them? Would the Imperium find the new drive useful for trade or military purposes, or just say "how quaint" and keep using the usual fuelhog jumpdrive?
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Old 06-07-2018, 05:39 PM   #2
Anthony
 
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Default Re: Slower fuel-efficient jump drive implications?

The big expense for merchant craft is return on investment, not fuel. Fuel can matter because of the large loss in cargo capacity, but outside of situations where you can't refuel regularly, that just caps practical jump number for merchant craft at 2-3 for most routes.
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Old 06-07-2018, 07:39 PM   #3
Fred Brackin
 
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Default Re: Slower fuel-efficient jump drive implications?

Quote:
Originally Posted by Anthony View Post
The big expense for merchant craft is return on investment, not fuel. Fuel can matter because of the large loss in cargo capacity, but outside of situations where you can't refuel regularly, that just caps practical jump number for merchant craft at 2-3 for most routes.
Yes, to be even vaguely competitive if you reduce the number of trips per year by a factor of 4 you have to reduce the cost of both building and operating ships by the same number.

there's a little of that to be made back by the increased cargo capacity but probably not as much as you might have hoped.

<grabs book>

On p.97 of GT:Starships there is a 20,000 dTon Liverpool-class dispersed hull bulk freighter. It carries 14000 dTons of cargo and 4000 dTons of fuel. Reduce fuel use by 90% and you only increase cargo by 25%. you do save 1.25 Mcr per jump but this is with a 2.750 Mcr ship that probably has to make something like Mcr 150 per year in profits. It's not nearly enough to make up for the reduced number of jumps.
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Old 06-07-2018, 08:30 PM   #4
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Default Re: Slower fuel-efficient jump drive implications?

OK, so the merchant ships won't want the Islands drive. What about the military? Yes, having your fleet unavailable for attack or defense four times longer is bad, but when you arrive you can assault the mainworld immediately while still having a retreat option. With conventional jump drive you either carry double fuel, attack immediately without a retreat option, spend a week at the gas giant refueling first, or split the fleet.

Of course, if feasible, you may want *both* drives on your warships. Or maybe battleriders with the Islands drive as a backup in case the mothership gets nailed.
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Old 06-08-2018, 03:21 AM   #5
malloyd
 
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Default Re: Slower fuel-efficient jump drive implications?

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Originally Posted by cptbutton View Post
OK, so the merchant ships won't want the Islands drive. What about the military? Yes, having your fleet unavailable for attack or defense four times longer is bad, but when you arrive you can assault the mainworld immediately while still having a retreat option. With conventional jump drive you either carry double fuel, attack immediately without a retreat option, spend a week at the gas giant refueling first, or split the fleet.
Note that you can effectively get that adding two weeks total to the mission (i.e. less than the delay for even 1 of the slower jumps) by jumping a fraction of a parsec short with a bunch of tankers, refueling enough for 2 J-1s, jumping in, completing the mission and jumping back to your tankers. I think the only place this is likely to be useful is on those tankers - if you can dispatch them early enough, they can get further without using more fuel than they can carry. If you are transporting anything other than fuel, I doubt there is much to be gained.

There is one place it might make some sort of sense though - if a slow J-4 engine weren't much bulkier or more expensive than a normal J-1 engine, well a J-1 ship design with one substituted in can make 4 parsec trips just as fast as it could before but with less fuel, so for regular runs along a main where you normally pass through several systems that don't have much worth stopping for there may be some applications.
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Old 06-08-2018, 03:41 AM   #6
Anthony
 
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Default Re: Slower fuel-efficient jump drive implications?

If it's enough cheaper per unit cargo capacity, it has the potential to fill a slow-boat market. However, getting it cheap enough probably requires really skimping on everything else on the vehicle, not just the drive.
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Old 06-08-2018, 10:19 AM   #7
Fred Brackin
 
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Default Re: Slower fuel-efficient jump drive implications?

It has occurred to me that this drive might be semi-attractive to a long-range colonization effort similar to the Sword Worlds. It's a one way trip and the travellers aren't interacting with known civilization anymore either. So they are on a completely internal schedule.

The problem with that might be that annual overhauls come after you've covered 1/4th the distance.

Maybe the islands drive needs less maintenance and they have a design for an overbuilt fusion reactor that can go for similar periods of time without major maintenance.

Colonization might be it though. The military would have little use for such a drive.

Incidentally, the crew can't be"sedated" in any conventional use of that word. They're either using a suspended animation drug or they're in low berths.
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Old 06-09-2018, 12:13 PM   #8
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Default Re: Slower fuel-efficient jump drive implications?

Quote:
Originally Posted by Fred Brackin View Post
Yes, to be even vaguely competitive if you reduce the number of trips per year by a factor of 4 you have to reduce the cost of both building and operating ships by the same number.

there's a little of that to be made back by the increased cargo capacity but probably not as much as you might have hoped.
More correctly, you have to up the costs.

I am working in CT because I have the spreadsheet built and know the numbers better.
Here's the basics for a 400Td J1 CT Bk5 design, crew only, rest pure cargo. B5 is Bk 5 costs; Alt is otherwise identical, but using 1/5 j-fuel, and rigged for 5 weeks, rather than 4.

Code:
J                 Bk5          Alt
J1 P1 TL15 HG                           
Jn/Pn               1          1
Tons              400        400
TL                 15         15
DesTL              15         15
Comp Model          1          1                     
Tonnages
Bridge             20         20
Computer            1          1
JD                  8          8
MD 1G               8          8
PP                  4          4
Turret (1x1)        1          1
Fuel, Jump         40          8
Fuel, PP            4          5
SR                 16         16
Cargo             298        329
MCrCosts
Hull 6 SL          32         32
Bridge              2          2
Computer            2          2
JD                 32         32
MD 1G               1.6        1.6
PP                 12         12
Turret (1x1)        0.2        0.2
SR                  2          2
MCr Total          83.8       83.8
                                  
Command             0          0
Plt                 1          1
Nav                 1          1
Engr                1          1
Gnny                           
Medic               1          1
Service             0          0
                                  
MoPymt         349167     349167
AM Share         6984       6984
Salaries        17000      17000
Fuel, Jump      40000       8000
Fuel, PP         2000       2500
LS, Mo          16000      16000
                         
Monthly Cr     431151     399651
Per Jump       215575.5   499563.75
                         
Per Ton           724       1519
                         
Per Mo Cr/Td     1312.59    1190.43
per J Cr/Td       723.41    1518.43
                         
Per Ton-Parsec    724       1519
Now, we can refactor this into passengers, assuming 13 mo/year, with one month down for maintenance, and no payments and unpaid leave in month 13... so we use 12 months.

Cargo profit ratio = 1000/724 = 1.38
Alt version at same ratio: 1518.43=2094.84, round up to Cr2100 per jump

a stateroom costs KCr500
monthly Maintenance and mortgage payment 2500/mo, 3125/5wk
LS per 2 weeks KCr2, for 4K/month or 5k/5wk
Cargo space lost 4td
A mid passage under CT needs is thus Cr1250 + Cr2893.64 + Cr2000 = 6143.64
[stateroom cost per jump + cost of cargo space replaced + LS]
refactoring for the alt: Cr(3125 + 6076 + 5000)=14201.
Keeping the CT profit ratio (KCr8 / 6143)=1.3021596317492563, MP should cost Cr18491.97 for J1 Round up to Cr18,500

HP: costs are 1 SR for passenger, and 1/8 of a steward and his SR per passenger.
So BK2+BK5 gives 1406.25 + 3255.345 + 2250 + 125 = 7036.6
[(stateroom cost per 2 weeks for 1.125 SR)+(cargo cost for 4.5 td)+(2.125 weeks LS)+(steward salary/(2 jumps @ 8 passengers))]
Profit rate for HP is about 1.42
the alt version (3125 * 1.125) + (1518.43 * 4.5) +(1000 * 5 * 1.125) + (2000 * 1.25 /8) = 3515.625 + 6832.935 + 5625 + 312.5 = 16286.06
keeping same profit ratio 16286.06 * 1.42 = 23126.2052
Rounding up to next 500 = 23,500.
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Old 06-09-2018, 12:29 PM   #9
Fred Brackin
 
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Default Re: Slower fuel-efficient jump drive implications?

Quote:
Originally Posted by ak_aramis View Post
More correctly, you have to up the costs.
Sorry, too many numbers without enough explanation. I can't make head or tail out of what you think you've demonstrated.
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Old 06-09-2018, 10:16 PM   #10
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Default Re: Slower fuel-efficient jump drive implications?

Even if you can double the cargo space, if you cut the number of jumps per year by 1/4 you’re still losing 50% of your revenue.

Fuel cost isn’t actually the major ship expense in Traveller.

More correctly, you have to up the costs

If you quadruple what you charge for cargo or passage, everyone else is still charging standard prices... and it takes you 4x as long to deliver... you won’t sell anything at all.
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