Ken Pick wrote a fantastic article for Freelance Traveller talking about using external mounts for cargo ships in Classic Traveller. I make heavy use of this in my own small ship settings. It’s fairly easy to do with large ships – loading up the 2000 ton Type TJ with a few thousand tons of external pods – but it gets more difficult with smaller ships. A 400 ton ship, for instance, that can carry 400 tons in pods is easy to make, but a 400 ton ship that can carry 800 tons in pods runs afoul of the Drive Potential Table, because it doesn’t have a line for a 1200 ton ship.

Rather than using Book 5 High Guard rules for ship construction, I wanted to stick with simple Book 2 ship construction, so I extended the Drive Potential Table, adding entries for 300 ton, 1200 ton, 1600 ton, and 6000 ton ships. For the 300 ton line, I divided the 600 ton line by 2. For the others, I multiplied the performance of the “half” entries by two, so 1200 ton performance is based on the 600 ton line, etc. The 6000 ton entry doesn’t include a build time, because it’s intended more to provide a line for a Type TJ with 4000 tons of external pods.

There are some oddities in the table, especially when you get into the heavier hulls, and I didn’t try to change those. They’re part of the character of the original game, and I wanted to stick close to that.