I use the following House Rules for Starship combat. Be warned though, it makes starship combat extremely deadly.
Armour Value
Halve armour values noted in the rulebooks (rounded up)
Armour Degradation
Armour degrades by 1 point per weapon hit. This means that over the combat, the armour becomes less effective and remains so until repaired. If three weapons hit, then armour is reduced by 3 points. The total offence of the hits is still calculated and compared against the armour value as normal. The reduction to the armour comes in to effect after the offence damage has been resolved.
Beam Weapons
Beam weapons cause the beam armour damage even if the hit doesn't cause damage to the ship itself. This is to simulate the beam cutting in to the ship's armour, but not penetrating the hull. The reduction to the armour comes in to effect after the offence damage has been resolved.