On 11Oct2019 0852, Cian Witherspoon wrote:
> 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.

Not so. It's no later than High Guard, 2nd edition (so late 1980). It
has a little table , the "Drive Tech Level Table":

            --Drive Number--
            1  2  3  4  5  6
Maneuver   7  7  8  8  8  9
Jump       9 11 12 13 14 15

Of course this was never back-ported into new editions of Book 1-3.

Jump range is also given as being limited by computer size, and that's
limited by TL as well, but not in such a way that computer TL limits
affect jump limits.

As for CT Book 2 starships, remember that the engineering section can be
any fraction of the ship's size, unless you're using a standard hull, in
which case it's limited to the listed sizes. Computer TL limits jump
size, and thus there is a TL limit, but it's not that at which the drive
is manufactured.

Going back to the original question about the Gazelle, at 300/400 Dtons
and looking at the tables for drives (I'm using /The Traveller Book/, so
the results might be different with other editions), a 300 DTon hull
isn't listed and so uses the same size drives as a the next bigger - the
400 DTon hull. Thus to get a J5 at 300 DTons we need a 'K' Jump Drive
and Power Plant, also enough to give J5 at the full 400 DTons. However,
the rules for fuel consumption use actual hull size, and say that 300 DT
and J5 needs 0.1 x 300 x 5 = 150 DTons, while 400 DT and J4 requires 0.1
x 400 x 4 = 160 DTons. Thus with 100 DT drop tanks and 60 DTons of
onboard jump fuel the Gazelle can do J4 with tanks, J5 with the tanks'
fuel but jettisoning the tanks (with 10 DT left over), and J2 from
internal fuel with no tanks.

--
Rupert Boleyn <xxxxxx@gmail.com>
Chief Assistant to the Assistant Chief