A stacking penalty is a penalty to the effect a module has on your ship. Stacking penalties take effect when you mount more than one module that affects the same attribute of your ship.
If you look in in Description pane of the info window of a module with a stacking penalty, it will have a phrase that is similar to: "Penalty: Using more than one type of this module or similar modules that affect the same attribute on the ship will be penalized." This means that adding additional modules that affect the same attribute will result in a lesser effect of each additional module after the first. This mechanic is in place to prevent ships from obtaining very high effects by simply using many of the same module.
For example, if a player were to add a module that boosted their weapon damage by 10%, then a second identical module, the second module would only add about 8.7% instead of the full 10%. The total increase would be 18.7% more damage instead of the expected 20%.
As a rule of thumb, adding more than four modules of a single type with a stacking penalty results in insignificant gains.
Stacking penalties implement diminishing marginal returns (see ) for bonuses. Every additional bonus added to an attribute has its effect diminished until there is practically no incentive to add another bonus.
The formula for the stacking penalty is:
S(n) = 0.5^[((n-1) / 2.22292081) ^2]
n = the nth module added S = stacking effect for this particular module addition
From this, we can know the following:
|Modules||Effect of nth module||Cumulative bonuses with N modules ,each giving 10%||Cumulative bonuses with N modules ,each giving 20%|
|1||100%||10 %||20 %|
Adding more than 3 modules of same type brings only very minor bonuses - fourth module will bring only 9% instead of 20% bonus (or 3% instead of 10%).
In general, modules will say whether or not they carry the stacking penalty. The following is a list of things to help you intuit more easily what will and won't have a penalty.
Damage Control Module
The damage control module is exempt from the stacking penalty, giving its full effect, when active, no matter what.
If a module with the stacking penalty is added along with a module that enhances the same effect by an absolute number (regular, non-percentile), the module with the absolute value will not be reduced in effect.
For example, I add a 1600mm Reinforced Steel Plates I module to my ship. This boosts armor by 3000 hit points. I then add two Regenerative Plating I modules, which boost armor by 6% each, with the effect of the second one being reduced. The effect of the 1600mm plates is unchanged.
Implants, Skills, and Boosters
Most implants do not have their effect penalized when stacked on top of modules that affect the same statistic. The exception is the Snake series of implants, which had the penalty added to prevent large speeds from being obtained.
CPU, Powergrid, and Capacitor Enhancements
- There was originally no stacking penalty. This caused all manners of havoc with players equipping many modules of the same type. Ships with many low slots would wield many damage enhancing modules for firepower that could instantly vaporize almost anything.
- The Red Moon Rising expansion tweaked the stacking penalty. Originally, it only diminished the second module, and didn't have much effect thereafter.