[Spaceships] Is This Legal?

[Ulzgoroth]

Originally Posted by Varyon

The appropriate reversal of that is that a larger Fuel Tank would get 3x the Delta-V. You know, the same thing as getting 3 Fuel Tanks.

If all you're looking for is a little more Delta-V, I suggest drop tanks. I don't think there's a RAW source for those, but they're pretty easy to write in - make a space"ship" that is streamlined with a single armor module (as normal), give it a normal sized External Clamp, and have everything else consist of Fuel Tanks. Boom, extra fuel.

You'll need to do some calculations, of course. Let's say you've got an SM+10 vessel with 6 fuel tanks, and you toss on an SM+10 drop tank. Your total amount of fuel is 12,000 tons, and the combined total weight of the vessel is 20,000 tons. That marks your fuel as equivalent to 12 Fuel Tanks (it's 60% of the vessel's mass). However, the multiplier on page 17 is a result of lost mass, and you're going to drop that drop tank as soon as it's empty. That means you're effectively losing 1 additional space, so use the 13 tank entry - a multiplier of 1.6. So, assuming you drop the drop tank as soon as it's empty, you'll end up with a delta-v of 2.88 mps.
This probably has some error margins in it, but should be close enough.

Doing the delta-V figuring piecewise is probably both more accurate and more useful.

Figure the delta-V for the ship+drop tank combo going through the fuel in the drop tank. Separately figure the delta-V for the ship without the drop tank going through its internal fuel. The ship with the drop tank will do those two things sequentially...