Couple of methods:
1. For ship-to-ship collisions I have special collider which detects only same type collider (with same layer) so you can ram other ships without flying over them (this one is without health change)
2. Ship's collider for detecting walls, bullets, or trigger for respawning (this one takes 2 points of life every frame when touching only EnemyAI ships)
2.1 On enemy ships it is only for detecting collisions with bullets and walls, for now it detects whether it's a cannon bullet or rocket (they don't have spark-activating rays for perfomance reasons)
3. Two rays on player's ship which handles sparks and by the way takes life according to actual rigidbody's speed (reacts only to walls)
Except for rays all of them are primitive box colliders with friction and constant rigidbody gravity turned off.