Stacking penalties refer to an effectiveness reduction that is incurred when using two or more modules or rigs that affect the same attribute. The more modules or rigs affect the same attribute, the less effective each additional module is; in practice, having more than three or four modules/rigs affecting the same attribute is not worth it.
Most (but not all) modules and rigs have show in their description if they are subject to stacking penalties.
Note that it is the stat bonus that is affected, not the module itself. For example, if you fit both a Nanofiber Internal Structure (boosts agility and velocity) and an Overdrive Injector System (boosts velocity), the Nanofiber's velocity bonus would suffer a stacking penalty, but not its agility bonus. Similarly with armour or shield resistance modules: if you fit an EM hardener, an explosive hardener and an omni-hardener (Adaptive Invulnerability Field or Adaptive Nano Plating): the EM/Explosive resistances from the omni-hardener would be stacking-penalized but the Kinetic/Thermal resistances would not.
Also of note is that module drawbacks (negative effects) can also be stacking penalized.
Effects of stacking penalities
Normally, the benefits of additional modules/rigs would be multiplicative. So if fitting one Speed Booster (a fictional module with nice round numbers to make the math easier to understand) module increases a ship's speed by 10%, fitting two of them would increase a ship's speed by 21% ((1 + 10%) × (1 + 10%) = 1.1 × 1.1 = 1.21), and fitting three would increase it by 33% (1.1 × 1.1 × 1.1 = 1.33).
However, due to the stacking penalties effect, the second, third, and fourth Speed Booster modules' effects are only partially effective (86.9%, 57.1%, and 28.3% respectively - see below for details), and would therefore only increase a ship's speed by:
- 10% × 86.9% = 9% for the second module
- 10% × 57.1% = 5.7% for the third module
- 10% × 28.3% = 2.8% for the fourth module
Therefore, the actual speed increase for the ship would be:
- One Speed Booster module: +10%
- Two Speed Booster modules: (1 + 10%) × (1 + (10% × 86.9%)) = (1 + 10.5%) × (1 + 9%) = +19.8%
- Three Speed Booster modules: (1 + 19.8%) × (1 + 5.7%) = +26.7%
- Four Speed Booster modules: (1 + 26.7%) × (1 + 2.8%) = +30.3%
However, the modules' bonuses still multiply, so even if the percentage increase of each subsequent module decreases sharply, the absolute increase of each subsequent module drops off more slowly. If we take a ship with a nominal speed of 100 m/s:
- Adding one Speed Booster module: 100 + 10% = 110 m/s, an increase of +10 m/s
- Adding a second Speed Booster module: 110 m/s + 9% = 120 m/s, an additional increase of +10 m/s
- Adding a third Speed Booster module: 120 m/s + 5.7% = 127 m/s, an additional increase of +7 m/s
- Adding a fourth Speed Booster module: 127 m/s + 2.8% = 130 m/s, an additional increase of +3 m/s
Stacking-penalized modifiers are applied one at a time, in descending order of strength.
The n-th modifier is multiplied by S(n-1), as follows:
- S(u) = e-(u / 2.67)2
- 1st mod: 100.0% effectiveness
- 2nd mod: 86.9% effectiveness
- 3rd mod: 57.1% effectiveness
- 4th mod: 28.3% effectiveness
- 5th mod: 10.6% effectiveness
- 6th mod: 3.0% effectiveness
As is clear, stacking more than 3 or 4 modules or rigs - unless you really have nothing else at all that you could fit there - that affect the same stat is fairly pointless, as your benefit is so tiny.
What suffers stacking penalties?
- Absolute effects are never stacking-penalized, only percentage effects. That is to say, things like +1 warp core strength, +1000 structure HP, +15 m signature radius, +400 GJ capacitor are not stacking-penalized because they are not percentage (%) effects.
- Only modules, rigs, and the effects of Command Bursts are stacking-penalized. Skills, ship bonuses from ship skills, implants, hardwirings, and boosters (such as Synth Blue Pill, Strong X-Instinct, and others) are not stacking penalized.
- Negative and positive effects are stacking-penalized separately. So, one +% and one -% effect to an attribute suffers no penalties, whereas with two +% and two -% effects, one of each would only be 86.9% effective. An example might be velocity modifiers: if you have one Overdrive Injector System on your ship (to increase your speed) whilst at the same time being slowed by a single Stasis Webifier from an enemy ship - both velocity modifers are 100% effective. If you are then affected by second Stasis Webifier (from the same or another ship) that second web will be only 86.9% effective.
It can be hard to tell exactly what suffers stacking penalties and what does not. For instance, the Overdrive Injector System II gives +12.5% velocity at a cost of -20% cargo capacity, and the description claims it suffers stacking penalties. The velocity bonus is stacking-penalized, but the cargo drawback is actually not. Similarly, the Warp Core Stabilizer II gives you one extra warp core strength at a cost of -40% targeting range and -40% scan resolution. It doesn't mention stacking penalty in the description, but the drawbacks are actually stacking-penalized.
We can learn from this that it is not the module itself which determines whether its effects are stacking-penalized, but rather the attribute affected.
Assuming the attribute they affect is actually stacking penalized, Command Burst modules are stacking penalized as normal, along with the rest of your modules and rigs.
Here's a handy table of what ship effects are stacking-penalized and which aren't; there are some weird exceptions which are further discussed below the table. Remember, it is only percentage effects from modules/rigs that are penalized.
Is <insert attribute> stacking-penalized?
|Powergrid (including reduced-PG-need effects)||no|
|CPU (including reduced-CPU-need effects)||no|
|Capacitor recharge rate||no|
|Energy Warfare resistance||yes|
|Module capacitor use||no|
|Shield recharge rate||no|
|Shield / armor / hull hit points||no|
|Shield / armor / hull resistances||yes|
|Shield boost / armor repair bonus||yes|
|ECM jammer strength||yes|
|Scan probe sensor strength||yes|
|Inertia modifier (agility)||yes|
|Duration (cycle time) bonuses (except weapons)||no|
|Missile launcher rate of fire||yes|
|Missile explosion velocity||yes|
|Missile explosion radius||yes|
|Missile flight time||yes|
|Turret rate of fire||yes|
|Turret damage modifier||yes|
|Turret tracking speed||yes|
|All optimal range (modules/turrets)||yes|
|All falloff (modules/turrets)||yes|
|Mining laser yield (including mining drone yield)||no|
|Drone control range||no|
- ^ Damage Control modules and the Reactive Armor Hardener module work slightly differently.
If you only fit one or the other (one Damage Control or one Reactive Hardener), then they are never stacking penalized. They will always give their full damage resistance effect, along with your most effective module that also gives it's full effect as explained above, followed by any other modules that will be stacking penalized. This is one reason why the Damage Control module is so popular; because it is always 100% effective.
If, however, you fit both, then one of them (whichever is less effective) will count as a second module and be stacking penalized accordingly (so, 86.9% effective). This is in addition to your normal resistance modules, of which one will give its full effect and the rest stacking penalized as explained above.
As an example, consider the following five modules all fitted to your ship and their resulting effectiveness: one Damage Control (100% effective), and one Reactive Armor Hardener (86.9% effective); one Armor EM Hardener (100% effective), one Energized Adaptive Nano Membrane (EM resistance 86.9% effective, other resistances 100% effective), and one Adaptive Nano Plating (EM resistance 57.1% effective, other resistances 86.9% effective).
- ^ The probe scan strength from Gravity Capacitor Upgrade rigs and Scan Rangefinding Arrays and Sisters & Tech 2 launchers are all stacking penalized, even though the rigs and launchers don't mention it. Sisters probes are not, because they are not percentage effects - the core probes have a base strength of 44 instead of 40 (or 22 instead of 20 in the case of Sisters combat probes).
- ^ Although the Nanobot Accelerator rig (to decrease armor repairer cycle time) says it is stacking penalized in Show Info, it isn't.
- ^ Turret tracking speed modules are stacking penalized separately to turret tracking speed rigs (NOTE: this may no longer be true, requires testing).