Do multiple EMP missile or beam hits stack?

Any idea? I’m trying to find out if it’s worthwhile to put more than one or two EMP missiles on a frigate.

EMP II missiles have a shock duration of 2400 which seems like it would put the enemy out of action for about the duration of one Cruiser Beam Laser cooldown if the numbers match up. Do multiple hits increase this duration or do you need to wait until the effect wears off before you can stun the enemy again?

Also, what does the EMP strength figure mean? Does it have an meaning if the target ship doesn’t have EMP shielding?

As near as I can tell, the duration is not increased by multiple hits, but the weapon cycle is fast enough that if all of your ships carry EMP weapons, you can keep enemy ships stun-locked. The EMP protection module seems to protect against the first EMP hit but not the second; the protection appears to stack with multiple protection modules.

Full disclosure: I prefer the cheap horde of ships strategy when dealing with an enemy fleet carrying EMP. That way I have plenty of ships in the fight with no money spent on the EMP arms race.