I have been playing around with multiple hyperdrive designs and I have found something you will probably find useful. If you are pressed for time at least read the second paragraph and the two lists at the bottom of the post.
I asked myself "What happens when you have two ore more different model hyperdrives in the one design?", fully expecting it to ignore one of them or do something silly like take the longest typical jump initiation time (jump time) and the slowest speed. To my surprise and pleasure, testing revealed it did what you would hope for and combined the best of both worlds. It used the best jump time from the on-board hyperdrives and the best speed, even if the two come from different hyperdrives.
I believe it also works for more than two drives but having more than two is literally quite redundant. But, having two hyperdrives has been mentioned in other posts as a wise design decision for redundancy reasons alone. This way, you can keep the best jump initiation time you have available (or the best you want to install given size/build time/cost/maintenance considerations) while utilising the speed of your latest hyperdrive model. All I can say is .
Actually, I can say a lot more than that. Here is a little guide I have written to the different combos at different tech levels. The style is pretty inconsistent at the moment as I wrote it primarily as a cheat sheet to use during my very slow research games (ie almost all of them). I may clear it up/flesh it out at some point, probably when I update it with new info from the expansion.
Once you have discovered the VelocityDrive ST3 there are pros and cons to using a Calista-Dal HyperDrive CD-9000 as your second hyperdrive rather than another VelocityDrive ST3.
Typical jump initiation of 4s rather than 5s. 1s doesn't seem like much difference but it is a 20% reduction and on average you will be 60000 closer to your next destination after the same amount of time. And that is per jump.
Calista-Dal HyperDrive CD-9000 is size 7, the VelocityDrive ST3 is size 8. Every unit of size counts.
VelocityDrive ST3 takes fewer resources to build (7 carbon fibre, 7 tyderios, 5 chromium, 7 steel vs 8 carbon fibre, 8 tyderios, 6 chromium, 7 steel for the Calista-Dal HyperDrive CD-9000). It is more expensive to make, takes longer and has a higher maintenance fee. But, the difference is not great and by that stage you will probably be rolling in the money. Maybe not worth it for every craft though unless you have to have the best available performance for all your ships.
I spelled out that comparison in detail because if you are like me that is the stage you will be at a lot of the time (even on slow research if there is a Dhayut empire in the galaxy as they are for the majority of my games the VelocityDrive ST3 is just a strategically timed war in mid-game away).
But, the same considerations apply almost every stage of hyperdrive research. It is unlikely you will be building many dual hyperdrive designs while you are using the Gerax Hyperdrive, but as when and in what amount you start using dual hyperdrives varies from game to game I will post details for all the levels. You can use more than two if you like, but I will only consider 1 and 2 hyperdrive designs.
1x Gerax Hyperdrive or 2x Gerax Hyperdrive. No other choices. These are the only type that will not feature in later designs.
Kaldos HyperDrive KH-3
1x Kaldos HyperDrive KH-3 or 2x Kaldos HyperDrive KH-3. It is smaller (9 vs 12), faster (23000 vs 20000) and has a better jump time (7s vs 15s) than the Gerax. The change in resource requirements (+1 steel, +9 argon, -8 helium for the Kaldos) does not justify ever putting another Gerax Hyperdrive on a design once you have discovered the Kaldos, unless maybe if the reactor is not good enough to even make full use of a Gerax.
Gerax HyperDrive ES
This is the first model where there is really some choice in what setup is best depending on your requirements/situation. From now on I will now give each choice its own blurb. I will only mention designs that do not use the latest drive if I think there might still be some application for them.
1x Gerax HyperDrive ES. Bigger (11 vs 9), longer jump time (12s vs 7s), faster (26000 vs 23000) and cheaper (-1 carbon fibre, -2 steel, +9 argon, -9 helium) than the Kaldos. Interesting trade
1x Kaldos HyperDrive KH-3. The mixed benefits of the Gerax ES means you might want to keep using a single KH-3 for some designs. Depends on the situation.
2x Gerax HyperDrive ES. Cheapest dual hyperdrive design at this level, but probably not worth it because the extra size will cost you in performance/other components and you have to wait for an extra 5 seconds for every jump on average.
2x Kaldos HyperDrive KH-3. Smallest dual hyperdrive design at this level. Might be worth keeping some designs using this combo if space+survivability outweighs speed in the circumstances. Probably just take it a bit easy on retrofitting these out when you discover the ES, wait until you have other important component upgrades to go with it.
1x Gerax HyperDrive ES + 1x Kaldos HyperDrive KH-3. Best speed and best jump time at this level combined. Intermediate cost and size between the other dual hyperdrive alternatives. Default choice for dual hyperdrive designs at this level. Speed loss if the ES is damaged is acceptable, ship can still jump away as quickly as possible.
Equinox HyperDrive EQ-700
1x Equinox HyperDrive EQ-700. Faster (28000 vs 26000/23000), smaller (7 vs 11/9) than the ES/KH-3 but more expensive than either (+5 chromium, -2 steel, +10 krypton, -9 helium compared to ES) and with a jump time in between (10s vs 12s/7s). Another interesting trade off.
1x Gerax HyperDrive ES. Might want to still use this for cheap designs (only where performance is not a consideration, otherwise other component costs will outweigh the savings). The difference in speed isn't that great.
1x Kaldos HyperDrive KH-3. Shorter jump time means greater survivability and the pro/con balance of ES vs KH-3 hasn't changed. Might find some use.
2x Equinox HyperDrive EQ-700. Smallest dual design at this level but most expensive and has a 10s jump time.
1x Equinox HyperDrive EQ-700 + 1x Gerax HyperDrive ES. Cheapest dual design at this level but a very specialised build as it trades 4 space for a few resources or 2 space + 3s jump time for even fewer resources. Consider carefully before building. The speed and jump time penalty if the EQ-700 is damaged is acceptable.
1x Equinox HyperDrive EQ-700 + 1x Kaldos HyperDrive KH-3. 2 extra space for 3s off jump time and it is cheaper. Default choice for hyperdrives at this level. Ship can still jump away as quickly as possible if EQ-700 is damaged and speed penalty is not bad for a hyperdrive 2 levels behind.
Kaldos HyperDrive KH-7
1x Kaldos HyperDrive KH-7. Faster (32000 vs 28000), better jump time (5s vs 10s), a bit bigger (8 vs 7) and maybe a bit more expensive (+1 carbon fibre, +5 lead, -5 chromium, +10 argon, -10 krypton) than the EQ-700. Generally worth it, default single hyperdrive choice for this level.
1x Equinox HyperDrive EQ-700. Trade speed and jump time for size and a little resource cost, might be worth it for some uses.
2x Kaldos HyperDrive KH-7. More expensive than the alternatives while offering no benefit except when one drive is damaged. Not really worth it unless you plan on spending a lot of time flying ships with damaged components or damaging them often. But, in circumstances where you can't afford the 1 extra space of a KH-3 and you don't want the EQ-700s potential jump time penalty or cost and size and are not issues it is preferred over using an EQ-700 as a spare. So really, it is the default premium choice at this level.
2x Equinox HyperDrive EQ-700. Smallest dual design at this level but still pretty expensive,has a 10s jump time and is slower than having a KH-7. EQ-700 + KH-3 is still better except when the extra 2 space really matters.
1x Kaldos HyperDrive KH-7 + 1x Equinox HyperDrive EQ-700. Smallest dual design that uses the KH-7 and cheaper than a second KH-7. Speed loss if the KH-7 is damaged is acceptable but if one hyperdrive is already damaged waiting an extra 5 seconds to jump might get you killed or at least cause a lot more components to be damaged.
1x Kaldos HyperDrive KH-7 + 1x Gerax HyperDrive ES. Bigger than the above alternatives and cheaper but with all of their drawbacks when the main drive is damaged and none of the advantages. ES as a spare drive was barely worth it at the previous level, now it is even more marginal.
1x Kaldos HyperDrive KH-7 + 1x Kaldos HyperDrive KH-3. Cheaper than using a EQ-700 as a spare but 2 bigger. Jump time loss if KH-7 damaged is acceptable but speed reduction of more than 28% is significant. Oddly the KH-3 is the default cheap spare hyperdrive at this level due to its good jump time relative to nearby levels, but this is the last time it makes a strong showing. The lesson is probably to upgrade to the KH-3 ASAP and then keep one on dual hyperdrive designs until you get the CD-5000. I have not studied retrofitting in any detail but I think the fewer components you change the better. You can also coordinate the move to mainly dual hyperdrive designs with the discovery of the ES to maximise efficiency.
1x Equinox HyperDrive EQ-700 + 1x Kaldos HyperDrive KH-3. Same size as 2x KH-7 and cheaper but slower and with a longer jump time. Also an additional speed or jump time penalty if one drive is damaged. Might be useful, but mainly when you get the KH-7 you have some breathing room in when you upgrade designs using these drives.
Calista-Dal HyperDrive Cd-5000
1x Calista-Dal HyperDrive Cd-5000. Faster (36000 vs 32000), smaller (7 vs 8), probably a little cheaper (+2 steel, +5 chromium, -5 lead, +7 tyderios, -10 argon) than the KH-7 but with worse jump time (7s vs 5s). Probably worth using instead of the KH-7 except where survivability trumps everything else.
1x Kaldos HyperDrive KH-7. Still a contender because of good jump time.
2x Calista-Dal HyperDrive Cd-5000. Smallest and cheapest dual design at this level, 7s jump time but suffers no penalty when one drive is damaged.
1x Calista-Dal HyperDrive Cd-5000 + 1x Kaldos HyperDrive KH-7. Speed of Cd-5000 with jump time of KH-7. The few extra resources and 1 extra space generally worth it. Still works pretty well if either drive is damaged. Default choice at this level.
2x Kaldos HyperDrive KH-7. Minimum jump time even when one drive is disabled, might be worth it when survivability is key. Again, no rush to upgrade away from the designs using these.
Equinox HyperDrive EQ-1200
1x Equinox HyperDrive EQ-1200. Faster (40000 vs 36000), slower jump time (8s vs 7s) with the same size and different but pretty equivalent resource costs to the Cd-5000. For designs that previously used 1x Cd-5000 probably worth upgrading to this.
1x Kaldos HyperDrive KH-7. Again, good jump time might still give this a role.
2x Equinox HyperDrive EQ-1200. Usual pros and cons of using the same drive as a spare and a main.
1x Equinox HyperDrive EQ-1200 + 1x Calista-Dal HyperDrive Cd-5000. Same size with similar resource cost to 2x EQ-1200 but shaves off 1s of jump time in normal operation and doesn't perform too badly when a drive is damaged. Usually preferred over 2x EQ-1200.
1x Equinox HyperDrive EQ-1200 + 1x Kaldos HyperDrive KH-7. 1 size for best available jump time, suffers a bigger speed or jump time penalty with a damaged drive. Default choice at this level.
Calista-Dal HyperDrive CD-9000
1x Calista-Dal HyperDrive CD-9000. Better speed (44000 vs 40000) and half the jump time (4s vs 8s) of the EQ-1200 with the same size and a similar amount of resources. You would be hard pressed to find a reason to use an alternative for single drive designs.
2x Calista-Dal HyperDrive CD-9000. Only reasons to use anything other than a second CD-9000 are cost and ease of retrofitting. Might be worth it in some circumstances but no other specific combinations are worth mentioning.
1x VelocityDrive ST3. Much faster (60000 vs 44000) and a definitely cheaper (-1 carbon fibre, -1 tyderios, -1 chromium) than the CD-9000 but 1 bigger (8 vs 7) and 1s worse jump time (5s vs 4s). Unless size or survivability are really important the more than 25% increase in speed makes up for it.
1x Calista-Dal HyperDrive CD-9000. Still useful if size is at a premium and/or jump time is more important than speed.
2x VelocityDrive ST3. Covered in detail earlier. Cheapest dual drive but biggest, suffers no penalty when one drive damaged.
2x Calista-Dal HyperDrive CD-9000. Smallest dual drive but most expensive, use if size and survivability trump cost and speed.
1x VelocityDrive ST3 + 1x Calista-Dal HyperDrive CD-9000. Covered in detail earlier. Default choice, best speed and jump time during normal operation. Trades reduced size for increased cost. Jump time penalty not bad if CD-9000 damaged, speed penalty if ST3 damaged significant but acceptable for auto-repair duration or getting to a dock for repairs.
Ok that took a while, but the matter is more subtle than just whacking 1 or 2 of the latest drives on all your designs. Most of the above has not really been tested in a play through, I am currently playing an epic game with very slow research and I am still stuck with the original Gerax. I will use my guide to help me play around during this game and check everything is as I have written it.
For a more simple view, here is a list of the best (IMHO) dual drive designs at each level for quick reference. I have not included any analysis but these should probably make up the bulk of your non-obsolete fleet:
2x Kaldos KH-3
1x Gerax ES + 1x Kaldos KH-3
1x Equinox EQ-700 + 1x Kaldos KH-3
2x Kaldos KH-7
1x Calista-Dal Cd-5000 + 1x Kaldos KH-7
1x Equinox EQ-1200 + 1x Kaldos KH-7
2x Calista-Dal CD-9000
1x VelocityDrive ST3 + 1x Calista-Dal CD-9000
So the real lesson is to use the latest drive as a main and the latest Kaldos as a spare. Once you discover the Calista-Dal CD-9000 use that as a spare while using the latest as a main.
One major area I have not covered in too much detail is the resources. I plan to test at some point whether retrofitting a component is easier when the required resources are similar. For example, is retrofitting a KH-3 to a KH-6 easier than a KH-3 to an ES? If anyone has played around with that I would be interested to hear about it.
The other area I have ignored is the different energy requirements of the hyperdrives. I presume dual designs use the energy requirement of the faster drive, but the design screen always uses the fastest speed and highest energy consumption. Testing energy use in practice is tricky. The energy consumption might affect your choice but depends on the reactors on the design. Also note that the different drives cover different amounts of space for the same energy usage. But, don't forget that slower drives use more energy for static requirements due to longer journeys even when they are more energy efficient than a later model.
As a final thought here is a list of the power requirements for drives with the distance they cover on a unit of energy:
Power, Distance/Power, Drive
62, 323, Gerax
75, 307, Kaldos KH-3
85, 306, Gerax ES
70, 400, Equinox EQ-700
95, 337, Kaldos KH-7
72, 500, Calista-Dal Cd-5000
78, 513, Equinox EQ-1200
66, 667, Calista-Dal CD-9000
60, 1000, VelocityDrive ST3