fuel-cargo hybrid space

[steve98052]

I recall reading something about spaces that can be used for fuel or cargo, without the limitations of collapsible fuel tanks.

For example, a modified Far Trader with 20 dtons of such space (and 20 dtons of normal fuel space) could carry 40 dtons of fuel for a Jump-2, or 20 dtons of fuel and 20 extra dtons of cargo for a Jump-1.

For another example, a modified Free Trader could supplement its normal 20 dtons of fuel with 20 dtons of such space, and be able to do a Jump-1 to deep space and another Junp-1 to cross a gap, without worrying about the fragility of a collapsible tank.

Does this exist in rules-as-written in a spot where I couldn't find it , or is it a house rule?

What are the rules, in terms of added space (such as the 1% used by collapsible tanks) and cost?

[baithammer]

Fuel/Cargo Containers From Book4 : Deep Space Exploration Handbook.

[Reynard]

I've been finding it useful in several of my designs especially with early tech designs. Explains how civilizations expand and exploit beyond the one parsec limit. Even ships of higher techs can benefit to surmount multi-parsec hurdles between clusters when they only feature 1 or 2 jumps. Once on the other side, they go back to carrying cargo immediately.

[steve98052]

Fuel/Cargo Containers From Book4 : Deep Space Exploration Handbook.

Thanks. Unfortunately, I either don't have that one or it's somewhere it shouldn't be.

What are the volume and cost figures?

[Condottiere]

If it's meant to be a reserve tank for a second jump, I'd fill it with water and have it processed during the one week transition.

[AnotherDilbert]

To make the fuel for the second jump optional, you want Collapsible Tanks (HG).

To make the fuel for the first jump optional, you want Fuel/Cargo Containers.


Example: To make the fuel in the Far Trader flexible you might have 10 dT regular tank for J-1, 10 (+0.5 Dt) Fuel/Cargo Container, and 20 (+0.2 Dt) Collapsible Tanks for a possible second jump.

When you just need to do J-1 only the regular tank is filled and you have 30 Dt cargo.
When you need to do J-2 the regular and the Fuel/Cargo is filled and you have 20 Dt cargo.
When you need to make 2 × J-2 you fill all tanks and have no cargo.

[Condottiere]

You could do a reverse rubber.

Use the fuel bladder to dump in goods into an empty fuel tank.

[AnotherDilbert]

What are the volume and cost figures?

1: The cost: 5 times that of Demountable tanks. If they were not better than Demountable tanks, why the big increase in cost?
2: The extra space. The tankage ends up taking up 5 percent extra space for the permanent piping. This piping could be connected to the fuel tank or Jump engine, so why not give it the usage for the Jump engine.

[phavoc]

You can also skip a lot of the problems by trying to have a hold able to contain LhD or dry goods and just have a hold that is capable of containing water. That water can be piped through your fuel processor to give you more range or duration with negligible extra expense. The only trade off is that it's not considered part of your fuel tanks, so your jumping range is limited to what your have in your primary tanks. But by the time you emerge from jump your tanks can potentially be full again to make another jump.

[steve98052]

So, it looks like the options are:

Regular fuel space, free, no space overhead, usable for jump, but usable for fuel only.

Fuel-cargo, extra cost, 5% space overhead, usable for jump, flexible.

Collapsible, extra cost, 1% space overhead, not usable for jump, flexible but slow, but fragile.

Demountable, extra cost, ?? space overhead, usable for jump, flexible but slow and must be store somewhere else.

Drop tank, extra cost, ?? space overhead, usable for jump, expendable or requires external storage and retrieval (at high technology level), extends jump range, or reduces jump range if not dropped, vulnerable to damage.

Is that all?

[DickTurpin]

Where did you see that Collapsible Fuel Tanks are fragile? The Highguard book doesn't mention that in the description.

[steve98052]

Maybe I'm confusing the rules about collapsible tanks with another edition. I thought I remembered something about hard maneuvers requiring a roll for possible rupture, and any fuel or cargo damage destroying them.

[AnotherDilbert]

So, it looks like the options are:

Yes, that's about it.

Regular fuel space, free, no space overhead, usable for jump, but usable for fuel only.

Default, but we can just as well use Demountable instead, for at least theoretically a little more flexibility.

Fuel-cargo, extra cost, 5% space overhead, usable for jump, flexible.

Collapsible, extra cost, 1% space overhead, not usable for jump, flexible but slow, but fragile.

Some overhead, maximum flexibility. I don't think Collapsible is all that slow or fragile, but since we can't use it directly we must have fixed tanks first.

Demountable, extra cost, ?? space overhead, usable for jump, flexible but slow and must be store somewhere else.

No overhead, tiny cost. Not all that flexible, but better than regular tanks, so why not?

Drop tank, extra cost, ?? space overhead, usable for jump, expendable or requires external storage and retrieval (at high technology level), extends jump range, or reduces jump range if not dropped, vulnerable to damage.

Tiny overhead in drop tank collars (0.4% of drop tank inside ship). Rather expensive, probably much too expensive for one time use, i.e. to drop. The only external choice. Cheaper than hull and allows us to make jump range flexible without wasting jump drive potential.

[Reynard]

Drop tanks are mounted both inside and mostly outside. If carried, they increase the tonnage of a vessel thus reducing the maneuver and jump potentials. That's why their main purpose is to be released just before jump so the ship has a full jump fuel load at the destination, drives at full potential and not using internal tonnage. Great mostly for military tactics or scouting. It's a complex way to make two jumps towards a destination over a rift.

[AnotherDilbert]

That's why their main purpose is to be released just before jump ...

Or else we keep them as regular tankage, like the Gazelle does (and has since early CT).

[Old School]

Seems like the drop tanks would be more viable for a regular run where you have infrastructure at both ends, i.e. a freight or passenger line that has terminals in both the starting and destination system, and a local tender vessel to pick up the empty drop tank, refill it, and take it to the next ship departing. Would allow vessels on a regular route to make longer jumps without dedicating all that room to fuel.

[AnotherDilbert]

Yes, using drop tanks and actually dropping them requires infrastructure at both ends.

Note that the drop tanks are quite expensive and crumbles more often than not, so it is questionable economically.

[Reynard]

Drop tanks incur a penalty to the Engineering (J-drive) check and not every ship is automatically TL 15. Also they make your ship unstreamlined.

[AnotherDilbert]

Drop tanks incur a penalty to the Engineering (J-drive) check and not every ship is automatically TL 15.

Yes, but at TL-15 that is DM-0. Using drop tanks is most attractive with high jump range which implies high tech drives anyway.

But, agreed, I would not really want to use drop tanks at TL-10 or so...

Also they make your ship unstreamlined.

No, partially streamlined, like many ships tend to be anyway. They can still land and scoop.

[AnotherDilbert]

Note that the drop tanks are quite expensive and crumbles more often than not, so it is questionable economically.

That has to be tested...

Simple conventional J-6 ship (120 Dt payload):



Same payload, dropping tank:



As we can see the conventional ship is more profitable, but the drop tank ship is cheaper so the yield on the down payment is higher.

The cost of replacing those tanks at MCr 3 a pop swamps even the mortgage costs of the massive jump drive of the larger ship...