Fuel consumption

[JAFARR]

Per Book 2:
At a minimum, ship fuel tankage must equal O.lMJn+lOPn, 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 (O.1MJn) allows one jump of the stated level. Ships performing jumps less than their maximum capacity consume fuel at a lower level based on the jump number used.

In real life, what vehicle actually does consume fuel at the manufacturer’s stated rate? None that I have ever owned. Do all vehicles of the same model get the same fuel consumption? And what happens to fuel consumption as a vehicle is used? However, in Traveller ship design rules, we are given the consumption guide above. In order for this rule to work and the ships designed with it to always succeed in making a jump of the specified distance, we should then conclude that this is a worse case situation. If that is the case, then can we take advantage of a “best case” or even a “normal case” situation to save on fuel costs? If so, how?

Again borrowing from real life, I would suggest that we can make 2 assumptions. (1) All vehicles have a variance in fuel consumption from the design, and (2) this actual consumption increases with time after overhaul. An extension of these assumptions is that the base fuel consumption will vary from overhaul to overhaul. The big question is, “Is there enough variance to be worth the extra record keeping?”

 

[beeber]

unless the last powerplant etc. maintenance is way overdue, i'd say no, it's not worth the effort in record keeping. unless we want to stat all powerplants & drives to be "AU/kiloliter" or whatever, then add in "mileage" degradation tables. . . .

 

[robject]

What he said, but, for a player's starship, a variation can add some interesting color.

 

[Zutroi]

Hmmmmm - as a problem for an engineer PC to solve, seriously out-of-spec fuel use could be a useful adventure handle, particularly out in a frontier environment without access to 'proper' diagnostic/repair facilities...

 

[rancke]

The plausible way to do it would be to say that power plant fuel was negligible, belowe the resolution of the ship design system, and filled up once a year during the annual maintenance.


Hans

 

[Swiftbrook]

DM: "OK, let's see" (rolls dice) "Your jump drive is not quite working up to peak performance." (rolls dice) "It just used 110% of normal fuel for that jump. Oh, um, you don't have that much. Um, so you jump drive just used up all your fuel, but you it didn't produce enougth energy to jump, sorry. You're power plant is now shutting down due to a lack of fuel. What do you do now?"



Too much of a headeach to worry about.

-Swiftbrook

 

[robject]

DM: "OK, let's see" (rolls dice) "Your jump drive is not quite working up to peak performance." (rolls dice) "It just used 110% of normal fuel for that jump. Oh, um, you don't have that much. Um, so you jump drive just used up all your fuel, but you it didn't produce enougth energy to jump, sorry. You're power plant is now shutting down due to a lack of fuel. What do you do now?"



Too much of a headeach to worry about.

-Swiftbrook

Definitely don't want to do it that way. Random per jump won't work, as you say.

Instead, do it like Foodrunner or Adventure 3 did it: due to malfunction or poorly maintained hardware, your ship requires 110% j-fuel to jump; the ship has demountable fuel tanks installed in cargo space to increase fuel supply, or perhaps can only make Jump-1 instead of Jump-2 until something changes. Or, alternately, you've got a rare hand-built Droyne model that only needs 90% fuel.

 

[JAFARR]

robject is more in line with what I had in mind. In a slightly different context, the US Navy once had a class on destroyers rated at 36 knots. That means you should be able to expect all ships of that class to perform within a knot or 2 of that standard. There was one, however, that did 45 knots. It was sent to the shipyards for disassembly and inspection to see why. Nothing any different from specs was found and it was re-assembled. Then it only did 41 knots. The people in charge decided to keep it as it was and not do any more inspections.

Now what I had in mind was a roll at inital trials to establish actual consumption. Lets say the rules are a worse case statement and most ships actually consume 95% of stated consumption. Roll D6. 1 = 100%. 2 through 5 =95%. 6= reroll D6. 1 through 5 = say 93%. 6 = 90%. Now after each annual mantaince recheck consumption. Roll D6 1 = 100% 2 through 5 = inital established consumption. 6 = D6/2 less than inital established consumption.

What does this work out to in fuel savings? Take a 200 ton J2 ship. Worse case is 40 tons of fuel per jump (2 Weeks) 2-5 = 38 tons or 2 ton savings per jump times 25 jumps a year @ a jump every 2 weeks with a 2 week overhaul = 50 tons of fuel a year. If the inital roll was a 6 the the savings will be at least 70 tons with shot at 100 tons a year.

Note that a best case inital roll (6 & 6) followed by a best case roll after (6 & 6) overhaul saves a whopping 127 tons for that year. The numbers are the same for a 400 ton J1 ship.

 

[JAFARR]

Or having that extra fuel in the tank for a power plant 2 ship works out to several extra days of power plant fuel in an emergency. 10 * 2 = 40 tons of fuel for 28 days or 1.43 tons per day for a LBB2 power plant 2. That is 1.4 extra days power plant fuel for a 200 ton J2 P2 ship that acually uses 95% of the stated consumption rate.

 

[Madarin Dude]

Well I would think there are different standards. If your ship was in Combat you woudl use more those fusion guns and lasers require a few extra kilowatts. But if you are in survival mode and the ship temp is just above freezing and using only green lights you might be able to stretch it out a bit.

 

[robject]

I'd suggest rolling once, after the unit is built (or, more likely, installed in the ship), and only apply changes in unusual cases, like so:

2D    Fuel consumption
2-3       85%
4-5       90%        
6-8       100%
9-10      110%
11-12     125%

Or even less common. Anyway, once you roll that then both you and the players have an idea as to whether or not that drive is going to give them trouble until they get rid of it.

"Oooh, looks like a General Products jump drive. That explains the extra fuel tankage. Better hire a good engineer this time..."

versus

"Oooh, looks like a Droynex jump drive. Lucky sonofagun."

 

[Swiftbrook]

A bit more consistent ....

Base Fuel Consumption

Roll after starship construction

2D    Fuel consumption
1-        80%
2         85%
3         90%        
4         95%
5-9      100%
10       105%
11       110%
12       120%
13+     Drive failure

Record the number you rolled for future maintenance records.

roll after each annual maintenance

2d      Change to Base Jump Fuel Consumption
2       -2 to base fuel consumption number (better fuel consumption)
3-4     -1
5-10    no change
11      +1
12      +2

Why the unbalanced roll after mainenance ... it's suppose to maintain and improve your drives.

Just an idea.

-Swiftbrook

 

[JAFARR]

In reguard to the last 2 posts: a ship designed to the minimum specs will never make the first jump if the first roll is 9+ for Robject's chart or 10+ by Swiftbrook's chart due to insufficient fuel capacity. Does this mean the shipyard replaces it at once?

Other than that, this is the idea I was trying to express. Maybe we need to fine tune the chart. As for the roll after overhaul, treat it as a check on quality if the overhaul.

BTW, Swiftbrook, what mods do you use to get the 1 and 13+ results?

 

[aramis]

A bit more consistent ....

Base Fuel Consumption

Roll after starship construction

2D    Fuel consumption
1-        80%
2         85%
3         90%        
4         95%
5-9      100%
10       105%
11       110%
12       120%
13+     Drive failure

Record the number you rolled for future maintenance records.

roll after each annual maintenance

2d      Change to Base Jump Fuel Consumption
2       -2 to base fuel consumption number (better fuel consumption)
3-4     -1
5-10    no change
11      +1
12      +2

Why the unbalanced roll after mainenance ... it's suppose to maintain and improve your drives.

Just an idea.

-Swiftbrook

Chart 2 modifies the die roll recorded and read on chart one, if I read this correctly... so nnual maintenance as a 1/6 chance of improving and a 1/12 chance of worsening drive fuel consumption.

 

[Swiftbrook]

In reguard to the last 2 posts: a ship designed to the minimum specs will never make the first jump if the first roll is 9+ for Robject's chart or 10+ by Swiftbrook's chart due to insufficient fuel capacity.

As for not making a jump with 105% or worse fuel consumption, I think there are a few designs where this would still work, you just cut into PP fuel each time. Also, it would work if you have a higher jump drive than 1. A jump-2 ship could still make a jump-1, but not necessarily a jump-2.

Chart 2 modifies the die roll recorded and read on chart one, if I read this correctly... so nnual maintenance as a 1/6 chance of improving and a 1/12 chance of worsening drive fuel consumption.

Correct

Just had another thought. What if a poorly maintained JD, as well as having a higher chance of miss-jump, has a longer time in jump space. I recall rolls for calculating jump time and ways of making navy fleets arrive "on time", but I don't have time to look them up now. Instead of providing better or worse fuel usage for a jump, you could increase or decrease the time spent in jump space. It takes a quarter pound of ground beef to make a "quarter pounder", it just might take longer if you're making it at home vs. a fast food restaurant.

-Swiftbrook

 

[aramis]

Just had another thought. What if a poorly maintained JD, as well as having a higher chance of miss-jump, has a longer time in jump space.
-Swiftbrook

Damages the setting too much, IMO. Under MT and TNE, minor misjumps already result in unusual time effects, BTW.

 

[robject]

Depending on your maintenance rules, I'd think that sub-optimal jump drives are probably half the price of the standard module; likewise super-optimal drives are probably twice the price.

So a Free Trader with a poor Jump Drive could be a few MCr cheaper than a standard one (and I'd take the extra fuel requirement out of cargo).