Calculating CR

In general, a boarding party encounter’s CR is 1 less than the tier of the enemy starship (e.g. boarding or repelling invaders from a tier 9 starship is a CR 8 encounter). Increase the CR by 1 if the boarded ship’s BR is at most 5 higher than the boarding attack modifier. Conversely, decrease the CR by 1 if the boarding attack modifier is at least 15 lower than the boarded ship’s BR.

These values assume that only some of the PCs are participating in the encounter, with the rest remaining at their posts. If the entire party participates, consider increasing the CR by 1 or more to provide the appropriate challenge.