Fuel per jump

[Hakkonen]

I'm going through the ship-design process in High Guard to make sure I understand it, and I've got a question about jump fuel. The book says:

The fuel tankage needed for a jump drive is related
to the size of the ship and the length of the jump, as
follows;

10% of the total tonnage of the ship, multiplied by the
maximum jump score of the drive

The result of this is the number of tons that needs to be
dedicated to jump fuel.

It doesn't say how many jumps you can get out of this amount of fuel. Is this the fuel for a single jump? Can I add more fuel for the jump drive, the way I can for the power plant?

 

[PsiTraveller]

The fuel is for one jump, so a 100 ton ship jumping 2 would use 20 tons of fuel.

You can jump the distance your jump drive is rated for (this is based on the tech level of the drive), and the percentage of drive your ship has. Yhis is on pg 14 of Highguard.

So the 100 ton ship with a jump 2 drive (TL11) needs 5 percent of the ships tonnage in jump drive (so 5 tons) plus 5 tons of drive, for 10 total tons of Jump drive. (described on page 15).

If you want to jump at Jump 3 distance you med higher tech drives, and 12.5 tons of jump drive, and 30 tons of fuel

 

[baithammer]

Minimum jump rules from Mgt 2ed Main Book

Jumps of less than one parsec (less
than three light years, or one hex) are possible, and
count as jump-1 for the purposes of Astrogation checks
and fuel expenditure.

 

[Hakkonen]

So the 100 ton ship with a jump 2 drive (TL11) needs 5 percent of the ships tonnage in jump drive (so 5 tons) plus 5 tons of drive, for 10 total tons of Jump drive. (described on page 15).

I'm not following this part. On p.15 of High Guard, it says jump drives must be a minimum of 10 tons. A 100-ton, jump-2 ship would have a 10-ton jump drive, the smallest allowable, plus 20 tons jump fuel.

Later on, in step 4 (Install Fuel Tanks), the book explicitly notes that it's possible to extend the duration of a ship's power plant by multiplying the basic 1-month supply; i.e., a 10-ton fusion plant burns 1 ton of fuel per month, so if the designer includes 3 tons of power plant fuel, the ship can run for 3 months between refuelings. There is no such note for jump fuel. So, can I simply note that my jump fuel tank is 40 tons rather than 20, and be able to make two jumps before I need to refuel?

On a related note, are jump fuel and power plant fuel the same thing? If my power plant tank is dry, can I divert fuel from the jump tank to keep my systems running in an emergency?

On a less-related note, I can't find a passage that says this explicitly, but I'm assuming the total tonnage (displacement?) of the ship's systems cannot exceed the hull's displacement. Is this correct?

 

[Reynard]

I have built several ship designs for an early jump one era that often carry fuel for a second jump. Yes, you make the first jump 1, exit out in deep space then make a second jump to reach a 2 jump destination. You need to provide extra fuel for the power plant for the extra time in jump and lose space aboard ship but you're going where you normally can't travel.

Both use hydrogen. You could run the power plant longer with the fuel originally reserved for the jump drive but then if you have less than what a jump calls for, no jump. You could use fuel marked for power plant use though that's often a lot less than what a jump uses plus do you really want to be in jump space with no fuel for the power plant?

"On a less-related note, I can't find a passage that says this explicitly, but I'm assuming the total tonnage (displacement?) of the ship's systems cannot exceed the hull's displacement. Is this correct?"

Yes and no. You could add more outside the hull such as external cargo mount increasing the total displacement above what the engines were designed for but you need to recalculate Thrust and Jump to the new size.

 

[DickTurpin]

On a related note, are jump fuel and power plant fuel the same thing? If my power plant tank is dry, can I divert fuel from the jump tank to keep my systems running in an emergency?

Yes, Jump fuel and Power plant fuel is interchangeable and usually come out of the same tank. Note that a power plant can use unrefined fuel with no penalty while a jump drive requires refined fuel to avoid the risk of a mis-jump.

On a less-related note, I can't find a passage that says this explicitly, but I'm assuming the total tonnage (displacement?) of the ship's systems cannot exceed the hull's displacement. Is this correct?

Correct, all of the ship's systems must be able to fit within the hull. There are some options that can add additional tonnage outside the hull (docking clamp with a ship attached, external cargo racks) but that means recalculating the ship's size for drive performance. Your jumo-2 ship may be limited to J-1 or even be unable to jump at all with too much extra junk strapped to the hull.

 

[PsiTraveller]

True: the 10 ton minimum is in the rules. This creates some wierd math situations with Jump 1 ships of 100 tons. 10 ton minimum drive tonnage means 5 tons of drive for calculating Jump capacity. So the 100 ton Jump 1 ship has 5 tons of Jump Drives. So this would alow the ship to jump 200 tons of material. (5 tons divided by 2.5% is 200 tons)

Everything conected to the ship at the moment of Jump counts towards the tonnage. Any ships clamped to the hull, or material in a Jump Net counts towards the tonnage.

If your ship needs 20 tons of fuel per Jump and you want to have enough fuel for 2 Jumps you will need 40 tons of Jump fuel. This will let you do 2 jumps before you ned to refuel.

Your power plant fuel is counted separately. It can be in the same tank, so your ship may have 41 tons of fuel and that would be enough for 2 jumps and the 1 ton of fuel provides fuel for 1 month of activity. Make sure you don't run out of fuel. You can use unrefined fuel in your power plant but using unrefined fuel for a Jump is dangerous.

The tonnage of a hull can be exceeded during jump by attaching stuff to the hull, but you need to calculate the tonnage for Jump, and for M Drive movement. The 100 ton ship moving 100 tons extra as described above is an example. Another way might be to have a Jump 2 ship and move more tonnage a Jump 1 distance.

Getting the maximum use out of your ship is an endless exercise in creativity. External cargo mounts, docking clamps, Drop Tanks, fuel bladders. There are a lot of ways to get more from your ship. Enjoy!

 

[Condottiere]

1. The default minimum volume for jump drives is established at ten tonnes; this can be adjusted downwards until seven tonnes with higher technology manufacturing processes.

2. The minimum volume for a stable jump transition is a hundred tonnes.

3. Ten percent of the volume per parsec to be travelled must be fuel that is consumed at the moment of transition; there are options as to from where that fuel can be drawn; fuel consumption can also be reduced at a higher technology level.