I feel like the impact of IM is way overestimated. It's 100% more supplies per month, so based on the *worst* parameter, it costs as much as having another ship of that type. However, this is offset by:
1) A 20% reduced deployment cost with no combat penalty; this alone can go a long way towards mitigating the supply use, depending on how much you use the ship
2) No increase in fuel consumption, compared to having a second ship
3) A 50% increase in crew required, vs 100% for a second ship
The downside is, of course, not having the 2nd ship. I mean, it's not a net benefit, but then again it is a d-mod. IMO it's nowhere near being unusable.
For a non-phase non-carrier combat ships, there are 9 d-mods to pick from. The first time we pick, there's a 2 in 9 chance of getting IM or EFI. Assuming we didn't get either, the next time we pick, it's a 2 in 8 chance. Thus, the probability of not getting either of those for 2 d-mods is 7/9 * 6/8, or around 58%. The chance of getting one or both of IM/EFI, then, is 42%. Unless I've miscounted the number of applicable d-mods? Or messed up something else?
I feel like you are way underestimating the impact of IM
That is costs as much as another ship of that type,
without providing any of the benefits of another ship, is exactly why it's so awful.
1) A 20% reduced deployment cost doesn't come anywhere close to mitigating the supply use. Even assuming no other d-mods, you'd have to deploy it 5 times a month to offset the maintenance cost; few ships repair & recover fast enough for that to be remotely viable (never mind the improbability of encountering the battles to enable that). 'No combat penalty' is also debatable, since I assume the increased crew requirement also translates to increases crew losses with hull damage.
2) Sure, this is fine, but it's also true of every other d-mod aside from erratic fuel injector, and the other d-mods don't double the supply cost of your ship. It's also a pretty minor benefit: fuel is
much cheaper than supplies, doesn't compete with salvage for cargo space, and requirements are pretty straightforward to predict, even aside from the significant assistance the UI provides for it.
3) This is not a bonus, it's a severe penalty. I don't care about the absolute number of crew required past the first few months of the game, I care about the size/ratio of the buffer between minimum crew and maximum crew. For nearly every ship, an additional ship is a benefit here; they increase the maximum by more than they increase the minimum. IM on the other hand strictly shrinks the buffer, on top of consuming it faster if you try to leverage that reduced deployment cost.
The increased supply cost carries the same problem as the crew: it consumes the precious buffer between supply requirements and total cargo space, while a second ship grows your buffer. And planning supplies for an expedition is already a challenge; underestimate your requirements and face potentially disastrous consequences, overestimate and you have heavy upfront costs and have to throw away loot and/or return early.
Taking a closer look at the d-mods, there are 9, but 3 are mutually exclusive structural damage mods. So my calculation is overly pessimistic, yours is too optimistic, and the right answer is more trouble to math out than I want to deal with
(I think yours is closer to right than mine, though)
Even if a ship has a single d-mod (IM), you can entirely mitigate the maintenance penalty if you have:
- Fleet Logitsics 2 (-25% maint)
- Field Repairs 3(-20% maint)
- Safety Procedures 3(-50% d-mod effect)
- Efficiency Overhaul (-20% maint)
This is exactly what I mean. You
need Field Repairs 3 and Safety Procedures 3 for IM to be tolerable. And every other d-mod also benefits from them as well; IM is still significantly worse than the others, just the margin is shrunk by enough to get away with not worrying about it. Most of the other d-mods can be mostly/entirely mitigated by just 1-3 points in a single combat skill, and easily supplied by an officer instead of the player character.