I made a ship that uses logic to quickly fire a whole bunch of shotguns, but it makes the game lag terribly when doing hull damage (No lag on shield damage). It's not a particularly insane setup, equivalent to 8x shotguns per second, having a 8x machinegun setup should produce the same kind of hull damage without lag so i'm not sure why it drops my fps to around 6. Tried ship on my own computer and a friend's server, same thing although his server is much beefier.
I've had capital battles with MUCH more firepower being slugged around so again, seems like a weird special case.
To reproduce, simply make a ship with can/mis (I was using explosive effect as effect, but the problem occurs without it as well) and shoot at something.