Ch. 16: Even at maximum thrust, the Twilight climbed slowly for a pilot used to starfighters. [...] The freighter shuddered as it climbed. [...] He tweaked the fuel injectors a little higher.
Ch. 17: "I can't outrun them," he said. [...]There's a lot of interesting information here.
"Let's jettison something," Ahsoka said at last.
Laser cannonfire streaked past the Twilight's nose, and another vulture droid buzzed the ship, so close to the cockpit viewport that Anakin jerked hard to starboard in pure reflex.[...]
"What? Can't dump fuel." Anakin checked the gauges. "It's not like it weighs enough to make a difference,and we've got to get to Tatooine."
"Water," she said. "Ballast."
"I didn't check the cargo bay."
"I'll do it," she said, and before he could stop her, she'd strapped Rotta in the copilot's seat and was making her way aft. "I jettison whatever I find, right?"
"Yeah. When you open the cargo hatch, I'll get a red warning light up here, and I'll just bring up the nose and let everything slide out. Don't waste time dragging any crates up to the tail ramp."[...]
The cockpit intercom buzzed. "Master, I'm in the cargo bay now."
"Good. What do you see?"
"Plenty of crates, and the reserve water tanks are showing full. That's five tons at least."
"That might do it. Open the drains on the tanks and make sure you're standing behind anything heavy that's going to slide out the back when you hit the big red button." [...]
"The console warning light flashed to life: CARGO HATCH OPEN. Anakin brought up the nose and the Twilight climbed steeply.
He thought he heard Ahsoka say something, but it was drowned out by the noise of air buffeting the bay. The freighter soared. Suddenly there were no vultures ahead of him, and he was heading into darker skies as the ship climbed.
1. Five tons, plus some unremarkable and presumably-draggable crates, are sufficient to significantly alter the performance of the Twilight and allow it to escape vulture droids, climbing to orbit over the course of the next page or so until it could make the jump to hyperspace after clearing the atmosphere.
The Twilight's volume is about 4,600 cubic meters, and per our recent ruminations on the density of the engine section of Star Wars vessels, we presumably have good confirmation that her mass might be somewhere in the range of 2300 to 4600 tonnes. And yet, five stated tonnes plus some unremarkable crates is sufficient to offload enough mass to make the ship, whose performance had been less than starfighter-ish previously, to soar and leave starfighters in its dust.
Perhaps our estimates of the mass are thus too high for this ship.
After all, consider that the performance went from slow to starfighters-suck. The jettisoned mass would thus have to constitute a very significant portion of the ship's entire mass. If a total of 100 tons were jettisoned in this circumstance, for instance, I would expect the total ship's mass be no more than 1000 tons . . . probably less.
(And you know, it makes some sense that an empty freighter would be a speed machine, though it's still odd a starfighter would lose to it. Unlike modern vehicles where you have to gear for certain performance preferences (towing requiring a completely different setup than high speed), a spaceship would not really have these concerns assuming the same basic thrust-generating technology was in use for a starfighter versus a freighter. Thus, a freighter would be designed with supreme engines simply in order to move the loaded bulk, but unloaded she'd be a high power-to-weight speed machine.)
2. Anakin notes that the fuel doesn't weigh enough to make a difference. But, he thinks five tons of water and some crates will.
Understand, even if the ship was carrying a full load of crates full of solid lead, it's irrelevant because Anakin's mental calculation was in regards to crates that Ahsoka could drag. Thus the mass and density of the crates in his mind would've been on par with the crates we see two clones always teaming up to carry around on Republic cruisers.
It thus seems unlikely that he would've been expecting even, say, another five tons of cargo. Thus, the total amount he expected to offload ought not have been more than ten tons or so.
Around ten tons of cargo thus outweighed the fuel on the Twilight, significantly enough to be in the "might do it" category versus the "won't make a difference" category.
2A. Also note that he references the need to get to Tatooine in reference to fuel jettison. And we know Teth and Tatooine aren't too far from one another insofar as the duration of the trip.
a. Let's say the ship had a full load of fuel. How much would be needed to reach Tatooine? If it's 1% of the ship's fuel, then 99% of the fuel weighs a lot less than ten tons. If it's 50% of the fuel, then 50% weighs a lot less than ten tons. If it's 75% of the fuel, then 25% weighs a lot less than ten tons. And so on.
b. It's also possible that he checked the gauges and saw that the ship barely had enough to get to Tatooine. In that case, it required much less than five or ten tons of fuel to get there. At rough maximum, then, given that set of parameters and that it didn't weigh enough to make a difference, the ship was going through a very small weight of fuel in order to make orbit and make the jump to hyperdrive to get to Tatooine, not to mention deorbit and landing.
Suffice it to say, it looks like our vessel mass is too high in the case of the Twilight from this example, and moreover we now have confirmation that Star Wars fuel is not very dense in the canon . . . not that we didn't already know that from RotS and the watery fuel scenes (deleted in the film but still present in the script, for instance). However, it's nice to have another confirmation.
Contrast this with Star Wars inflationists who insist that Star Wars fuel is hyperdense magic material . . . and of course contrast the five tons making a performance difference with their claims of Star Wars vessels having densities many times that of water. Such 'fanatics' (to borrow a phrase) can point to whatever they like . . . the canon is what it is, even if they don't understand how it works from their certain point of view.