The first available drive that provide J4 capability in a 600 ton hull is the model M. In a 400 ton hull, the same model M provides J6. Fuel usage is the 240 tons required for J6 at 400 tons. Just think of it this way, which is implied by the table: each higher letter drive outputs a certain amount of jump power, which is divided by the tonnage of the ship to provide a jump range, and j6 is the maximum survivable. 
Now, in modern canon, the actual ability depends on what TL the drive was manufactured at, but that’s just MT onwards. 

On Thu, Oct 10, 2019 at 12:07 Thomas RUX <xxxxxx@comcast.net> wrote:
Hello again Phil,

I do find the what-if or what-is the smallest dT hull that could J5 or J6 in a single jump interesting, but with my track record on my badly worded intro and question this might take a while to answer.

Does the hull have to meet all of the design requirements in CT LBB 2?

In CT LBB 2 1977, 1981 page 14 the discussion of the basic controls indicates that "In addition, the model number indicates the highest level of jump that can be achieved by the ships. For example, a ship must have a Model/4 computer before it can perform jump-4, in addition to the proper size drive."

Is the caveat for the TL restriction based on the Computers Table on page 22 has a Model/5 available a TL B (11) and Model/6 computer available at TL C (12)?

Going back to the 600 ton hull J4 drive being installed in a 400 ton hull that results in a J6 capability which fuel requirement is used. The 360 tons of fuel for the 600 ton hull, the 240 tons of fuel for a J6 for the 400 ton hull, or the 160 tons for a J4 on the 400 ton hull?

Tom Rux
On October 10, 2019 at 7:54 AM "Phil Pugliese (via tml list)" <xxxxxx@simplelists.com> wrote:

 
Here's another 'what-if' that you might find interesting.

Using CT LBB2 rules, what would be the smallest dT hull that could J5 or J6 in a single jump?

p.s. I just remembered that there's another 'caveat'. It is possible that 'TL' restrictions could come into play to restrict max J capability.

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On Thursday, October 10, 2019, 06:31:28 AM MST, Thomas RUX <xxxxxx@comcast.net> wrote:

Morning from the Pacific Northwest Phil,

I agree that the phrase "regardless of the hull size" is wrong, but it was not clearly wrong to me until you clearly and concisely showed me it was wrong. My apologies for being so dense.

I'm think my calculation for the fuel load using the 600 ton hull J4 drive on a 400 ton hull is probably wrong too. I used the six parsec number that would have been used if the drive had been designed for a 400 ton hull. Using the 600 ton hull four parsec number the fuel tankage would be 160.

Thank you for your help.

Tom Rux


On October 10, 2019 at 5:21 AM "Phil Pugliese (via tml list)" <xxxxxx@simplelists.com> wrote:

 
That may have been the 'question' per se but here is the full statement ;

"Hello all,

Back in when I picked up Traveller my impression, which was reinforced by the GM, has been that a J4 drive has a maximum range of four parsecs regardless of the hull size that it is installed in.

Can a J4 drive built for a 400 ton hull allow a 300 ton hull to make a five parsec jump?

Tom Rux"

So, OK, the answer to the 'question' is 'no' wrt the specified details. 

However, I was primarily addressing the inaccuracy of the previous sentence which was & is clearly wrong.

So, while in the specific example of a J4 initially installed in a 400 Dt hull will not allow a 300 Dt hull to achieve J5, it is quite possible to raise the J capability of LBB 2 J-drives by installing them in smaller Dt hulls.

Hence, a J4 drive does NOT have "a max range of four parsecs regardless of the hull size"  & that long-ago GM was dead-wrong.

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On Wednesday, October 9, 2019, 08:54:47 PM MST, Thomas RUX <xxxxxx@comcast.net> wrote:


Hello Phil,

The question was: Can a J4 drive built for a 400 ton hull allow a 300 ton hull to make a five parsec jump?

CT LBB 2 Building Ships pages 20-21: "1. Custom hulls with mass displacements other than the hull sizes shown on the drive potential table are treated as the next larger size. The maximum hull size possible in these rules is 5000 tons."

In CT LBB 2 a J4 drive sized for a 400 ton hull will not allow a custom 300 ton hull to make a five parsec jump.

A CT LBB 2 600 ton hull with a J4 drive can use drive types M, N, or P. Using either a 600 ton J4 type M or type N drive appears to be able to allow 400 ton hull to make J6. The M type J4 drive requires 65 tons of hull space and the type N use 70. The two jump drives exceeds the 400 tons available Engineering space of 50 tons by 15 and 20 tons. A 400 ton hull J6 drive requires 0.1 x 400 x 6 = 40 x 6 = 240 tons reducing the Main Compartment's 350 tons to 110 tons and stealing 15 tons leaves 95 tons. Installing the smallest Power Plant  4 is Type H and requires 25 tons of space 95 - 25 = 70 tons of unused space. The power plant requires 60 tons of fuel which leaves 70 - 60 = 10 tons of hull space. A 400 ton hull has a 20 ton bridge and requires a Model/4 computer of 4 tons 10 - 24 = -14.

The use of a J4 drive built for a 600 ton hull on a 400 ton hull will not jump 6 parsecs there is not enough room to fit the required components.

Tom Rux

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