An expedition does not choose any ship from the full catalog. On a Ships outcome, it selects 1–3 types only from ship types that were already present in the sent fleet.
How does this expedition outcome work?
If you do not send a particular ship type, that type cannot be selected by the ship-find mechanic on that expedition. The sent composition therefore acts as the pool of eligible reward types.
What are the default parameters?
After a type is selected, the number found is calculated separately from the quantity of that type sent and then modified by the expedition bonus.
What determines the result?
This lets you design expedition composition around particular ship finds, but it also means those same units are exposed to negative expedition outcomes.
How should you use this in practice?
Default event weights are only the built-in starting configuration. An administrator can change them, so the real frequency in your universe can differ from percentages calculated from the default total weight of 112.
What should you watch out for?
Do not treat a single expedition as a guaranteed return on investment. The outcome is random, and even a positive event can be limited by fleet parameters, bonuses or free cargo space.
Related FAQ: How many ships can an expedition find? · How does a black hole work on an expedition?