Say I need to supress the piracy on system Zulei Cro:

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I want to calculate the number of corvettes I need to have patrolling the system, but my math is somehow wrong.

So the system is currently unprotected because the Trade Value (65.16) is greater than the Piracy Suppression (0). So if I add 7 corvettes (7x10=70 Pirate supression) the system will be secured. Right?

Now look at this other system:

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It has two corvettes (The Stream Fleet) patrolling for 20 Piracy Supression and the Trade Value is 52.48. So two corvettes are enough to supress the piracy on this system.

This tells me that the system Zulei Cro may need less than 7 corvettes to protect it.

My questions are:

  • How can I calculate the Pirate Supression needed reliably?
  • Does the Trade Protection provided by nearby stations affect the Pirate Supression formula somehow?

1 Answer 1


Piracy starts at 0, and slowly increases over time to 25% of the value of the trade route value, so the first answer is that you have correctly deduced you don't need 7 corvettes for Zulei Cro, you need 2 at most.

Assuming linear growth, that means piracy grows 2.5% per year, since it maxes after 10 years.

As I understand it, Trade Protection has no effect on piracy -- rather, a Trade Protection value of X means that the first X of trade can never be affected by piracy. This is why Zulei Cro, despite the -.01 piracy, lists 0.00 as the Piracy Effect -- the starbase you have there is protecting the trade so that the pirates don't meaningfully affect things.

Piddahfir, by contrast, has no piracy because your fleet has suppressed it back down to 0 (13.12 - 20, floored to 0), and it will slowly start to increase again once The Stream leaves. If you upgrade Piddahfir from an outpost to a starbase, it too would have built-in Trade Protection.

More info here on the Stellaris wiki

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