I set out to create a very complex ship whose sole purpose was to crash the game.  It succeeded.  The ship is shown below (inspiration should be obvious).

This ship has a full three rows of parts.  The fighters actually launch at 45 degrees to the main axis of the ship using oscillate (impressive when they launch, less so when they reverse direction and go back).  The turrets scattered all over the ship, top and bottom, all rotate (360 degrees) and elevate (using oscillation set to 45 degrees).  Turrets on the sides are symmetrical, the ones in the center are not.  Rotation speed and elevation speed is different for every turret.  One turret in front actually fires (using a glowing yellow Terran rod piece set to oscillate).

Here is the design (above) in game.  As a single ship, the animation worked as it appeared in the ship designer.

However, when placed in a fleet, the animations changed.  In the above image, one fighter each in the top and right hand ships are canted at an angle.  In the left hand ship, the animation changed speed so that the fighters did not launch together.  In different fleets, and after moving, the changes to animation varied.  Sometimes a fighter would disappear altogether.  Other times, some of them would be canted at weird angles.  Sometimes one ship looked just right but the others did not.

Gameplay

By turn 167, I had 47 of the ships in the game with no obvious impact to play.

Around turn 185 (probably about a hundred ships) I started to notice a little lag on the main map, but wasn't really sure.

By turn 190, there was no doubt.  That game was lagging on the main screen.  Other parts of the game (end turn, colony screen) did not lag.

By turn 201, with all of my colonies producing this ship and about two dozen fleets on the map, the lag was getting really bad (main map only).

On turn 202, the game crashed to the desktop (I will try to recreate the crash while running debug).

Well, that's it.  I've had fun designing ships (I don't get to be very creative in my day job) and testing them, but back to work tomorrow.  Hope this helps.