In my next session, I'm going to have a starship battle in which the PC's, in a slightly below perfect (60 crew, 70 morale) cruiser, take on some void-pirates. Having never GM'd a Starship battle. I'm a little in the dark as to how to go about balancing a combat.

Do people have any useful tricks for determining the relative power of two sides of a starship fight?

Otherwise, what combination of frigates and/or raiders would make a good challenge for a cruiser?

The sucess of NPC frigates vs PCs in a cruiser depends on 3 factors:

1)If NPC are using the default crew skill of 30% they are simply toast against PCs. Be sure to give the NPCs at least a 40%. Be smart use lock on and put your backs into it.

2)The NPCs need to use good tactics. They should be scanning the PCs ship and targeting their crits to the shields and weapons.

A pair of frigates should be quite dangerous to a cruiser if they manage to stay behind the cruiser, and regularly get it in their forward arc. Also remember ship combat is rarely to the death the enemy ships should use the disengage manuver if they get too damaged.

A quick-and-dirty rule of thumb is to take the number of guns each ship can bring to bear (I know, the system is abstracted, so just take the total Strength value, i.e. the maximum possible number of hits they can inflict in one turn) and square it to find an approximate firepower value for that ship.

The firepower of individual ships can be calculated in this way (it's a truism going back to at lest the Napoleonic wars, and quite adequately captured by BfG, and the RT starship combat rules are essentially BfG for small actions), and for a roughly even fight, discounting intangibles like crew skill and morale, and with no other significant force multipliers, the ratio of firepower between the sides should be roughly 3:2 against the PCs' cruiser.

The NPC DDs and FFs should be making firing passes on the cruiser from astern, coming in on bearings ~50° apart (so at least one of them is in the cruiser's rear arc), and they shouldn't be afraid to sacrifice one or more of their number to cruiser fire if it gives the rest a better chance. I'd also recommend having them use Silent Running and/or local "terrain" to better get into position for the initial strike (and, for that matter, disengaging later).

Thanks, guys. Good advice specifically on enemy tactics.

For cruisers I always insure that the enemy ships have both lances, and macrocannons. You fire the macrocannon's 1st to take down the void shield(s) then use the lance punch through armor and get the crit. A couple of frigates with good rolls can rapidly crit shields and weapons....

An even more nasty tactic is to go all lance with raiders, and have a good command bonus. Then simply rush the cruiser, and take down the shields with hit and runs. Then shoot the lances independently. The lance's low crit threshhold means the cruiser could be getting 2 crits per raider every round.... This doesn't work well on ships that have the maze option and the attackers can't target their crits.